A PSYCHOPHYSICAL STUDY TO DETERMTNE MAXIMUM ACCEPTABLE HAND IMPACT FORCES DURMG DOOR TRIM INSTALLATION:

EFFECTS OF HAM> POSTURE AND W A C T GLOVES

BY

Marc Patrick Henry Joseph Murphy

A Thesis Submitted to the College of Graduate Studies and Research

through Human Kinetics in Partial Fulfiilment of the Requirements for

the Degree of Master o f Human Kinetics at the University o f Windsor

Windsor, Ontario, Canada

1999

O Marc Patrick Henry Joseph Murphy, 1999

National Library 1+1 of Canada Bibliothèque nationale du Canada

Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. nre Wellington OttawaON K I A W Oltawa ON K1A ON4 Canada Canada

The author has granted a non- exclusive licence aliowing the National Library of Canada to reproduce, loan, distribute or sell copies of this thesis in microfom, paper or electronic formats.

The author retains ownership of the copyright in this thesis. Neither the thesis nor substantial extracts fkom it may be printed or othenvise reproduced without the author's permission.

L'auteur a accordé une licence non exclusive permettant à la Bibliothèque nationale du Canada de reproduire, prêter, distribuer ou vendre des copies de cette thèse sous la fome de microfiche/film, de reproduction sur papier ou s u . format électronique.

L'auteur conserve la propriété du droit d'auteur qui protège cette thèse. Ni la thèse ni des extraits substantiels de celle-ci ne doivent être imprimés ou autrement reproduits sans son autorisation.

ABSTRACT

A Psychophysical Study To Determine Maximum Acceptable Hand Impact Forces During Door Trim Installation:

Effects Of Hand Posture and Impact Gloves

Marc P.H.J. Murphy University Of Windsor, 1999

Advisor: Dr. J.R. Potvin

Upper extremity work related musculoskeleta1 disorders are significant problems for

industri al u.orkers. Previous research has identified possible risk factors for upper extremity

disorders. to include repetition, force, and awkward postures. To add to this, the hand is used

within trim and assembly plants to impact and seat parts into place which expose the hand to high

forces, local stress, and shock. This research investigates the maximal hand forces that people

find acceptable for these tasks and examines how these tolerances may change with hand posture

(palm vs ulnar) and protection (bare hand vs glove). A simulation device (Potvin & Chiang,

1998) was used to measure the time-history of the hand impact forces required to insert pushpins

during door trim panel installation. Acceleration data was recorded using a modified wrist brace

which subjects wore. The findings of the experiment found glove use to increase tolerance and

decrease severity with males choosing impact tolerances much higher than females with similar

impact se\lerity. Males were also found to benefit more corn glove use with females being more

consenrative. Posture produced some interesting findings, with palmer impacts resulting in higher

acceptable force impulses and peak accelerations. The implications of these posture results for

impact seventy were not clear and require funher study.

1 would first like to thank Dr. Jim Potvin for his guidance and insight. 1 thank Dr. Jim

Pot vin for being a great fnend and advisor whose knowIedge of and passion for ergonomies has

been a source of inspiration. His faith and belief in me was unsurpassed, and his high standards

and level of espectation pushed me to perform beyond my preconceived limitations,

I thank Dr. Weir and Dr. Taboun for their criticisms about my thesis and in doing so have

made this experience a mernorable one that 1 will not soon not forget. Their constructive

suggestions increased both the quality and comprehensiveness of this manuscript. I thank a11 of

those students who took the time to be subjects. A hear-felt thank you goes to al1 my classrnates

& roomnlates who provided me a listening ear when 1 was ranting and raving and complaining

about al1 the typical thesis h a l s and tribulations.

I wouId like to thank my Morn & Dad for always brimming with unwavering support,

belief. and confidence in my abilities, and for countless 'good vibes' and 'pick me ups' when 1

felt othenvise. 1 thank my Mom and Dad again for instilling in me the work ethic 1 needed to

sumi~~e , for your quiet trust and faith, and for giving me a kick in the pants when 1 needed it. I

could not have done it with you.

It is now complete, so today.. .. . .

Fil1 with mingled cream & arnber, 1 will drain that glass again

Such hilarious visions clamber Through the chambers of my brain

Quaintest thoughts-queerest fancies Corne to life and fade away

What care 1 how time advances? I'm drinking ale today!

Edgar Ailan Poe

TABLE OF CONTENTS PAGE

Abstract

Table of Contents .

List of Tables

List of Figures

Chapter 1 : INTRODUCTION .

1 . 1 Background

1.2 Purpose

1 -3 Hypotheses

1.4 Limitations

1.5 Definition of Terms

Cliapter 2: REVIEW OF LITERATURE

2.1 Upper Extremity Disorders

1 ) Shoulder, Am, & Elbow . 2 ) The Wnst & Hand .

2.2 Anatomy .

1) impact Ann Position and Action . 2 ) The Hand & Wrist 3) Nerves & Blood Vessels .

2.3 Shock Attenuation

2.4 Impact Protection .

2.5 Psychophysics . vi

Chapter 3: METHODOLOGY .

3.1 Expenmental Conditions .

3.2 Subjects .

3.3 Protocol .

3.4 Data Collection .

3 -5 Data Analysis .

3 -6 Statistical Analysis

Chapter 4: RESULTS .

4.1 Variability Data .

4.2 Force Variables -

1 ) Peak Force . 2) Force Impulse - 3) TTPK Force 4) Load Rate Force .

4.3 Acceleration Variables -

1 ) Peak Acceleration . 2) Acceleration Impulse 3) n P K Acceleration. 4) Acceleration Load Rate -

4.4 Subject Effective Mass. .

4.5 Recommended Impact Limits .

3.6 Correlation Data

Cliapter 5 : DISCUSSION.

vii

5 -2 Hypo theses

5 -3 Limitations

5.4 lnteresting Findings

1) Posture . 2) Controlled Variables 3) Recommended Acceptable Impact Lirnits .

Chapter 6 : SUMMARY & CONCLUSIONS .

6.1 Summary Of Methodology

6.2 Surnmary Of Results .

6.4 Future Proposals .

References .

Appendices .

Appendix A -

Appendix B .

Appendix C .

Appendix D .

PAGE

60

Appendix E .

LIST OF TABLES

Table 2.1 : Movement of the upper m during door trim instalIation. The

in ternal rot ators, elbow flexors/extensors and pronators of the ann. .

Table 4.1 : W i thin subject coefficients o f variation (CV) for each variable,

expressed in percent values (%), Values have been pooled across ail conditions,

n i t h i n each gender, posture, & protection (n=16). .

Table 4.2: Recornrnended threshold limit values for e2ch variable based

on 75'" percenti le values at 5 impacts/minute. Female values should generally

be used unless males are perfonning the task exclusively. .

PAGE

LIST OF FIGURES PAGE

Figure 2.1 : The structure of the carpal tunnel and hand. Neurovascular

structures. including the median nerve, uinar nerve, and uinar artery pass

through the carpal tunnel bounded by the flexor retinaculum and the carpal

bories. Compression due to impacts to the ulnar and palrnar side of the hand

can effect these under lying tissues. . 15

Figure 2.2: Carpal bones of the hand. Compression due to impact can create

degenerative changes with the wrist joint. . 16

Figure 2.3: During impacts there are many muscles that are of concern within

the Iiaiid. During industrial door trim seating tasks impacts are performed using

ille palm or the ulnar side of the hand. During these motions the abductor

pollicus brevis, opponens pollicis, flexor pollicus brevis, opponens digiti

minimi. palmaris brevis, abductor digiti minimi, and the flexor digiti minimi

brevis are under constant mechanical stress. . 16

Figure 2.4: High darnping in a polymer reduces the impulse peak of a shock wave

over a larger time fiame. Sorbothane fùnctions to reduce the impact force and

brings the mass to rest slowly, allowing better protection. . 26

Figure 3.1 : A schematic illustration of the p a h e r impact hand position. .

Figure 3.2, A schematic illustration of the ulnar impact hand position.

Figure 3.3: Al1 independent variables looked at in the curent shidy.

Figure 3 -4: A schematic illustration of the door trim panel installation

Simulation de\ice and the pressure adjustment dia1 to control resistance. .

Figure 3.5: Sample acceleration-time history with measured variables

indicated.

Figure 3.6: Sample force-time history with measured variables indicated. .

Figures 4.1 a &k b: Sarnple time-histones for peak force and force

impulse over the course of one 2-hou data collection session for one

male subject. .

PAGE

34

PAGE

Figure 1.21 8r b: Sample time-histories for peak acceleration and

acceleration impulse over the course of the final 2-hou data collection

session for one male subject- .

Figure 4.3: A comparison of the mean values for gender (male vs female)

for peak forces exerted by al1 subjects during the study. Data has been pooled

across al1 conditions for peak force (Each gender bar n=8). Al1 error bars

represent the standard error. .

Figure 4.1: The effects of h k d protection and the development of peak

force during the final 2-hour collection session. Glove being greater than the

bare hand. (Each protection bar n =16). Al1 error bars represent the standard

error. .

Figure 4.5:Shows the interaction between protection and gender for Force

Inipulse (Each gender value for bare & glove n=8). Al1 error bars represent the

standard error.

Figure 4.6: The Force Impulse means for posture for al1 subjects during the

final 2-hour collection session (Each posture bar n=16). Al1 error bars

represent the standard error. .

xii

PAGE

Figure 4.7: The mean TTPK Forces for the protection conditicn of the

final 2-hour collection session (Each protection bar n=16). Al1 error bars

represent the standard error. .

Figure 4.8: The mean Peak ~cceleration values for the protection

condition for the final 2 hour collection session (Each protection bar n=16).

Al1 error bars represent the standard enor. .

Figure 4.9: The mean Peak Acceleration values for the posture condition for

the final 2-hour collection session (Each posture bar n=16). Al1 error bars

represent the standard error. .

Figure 4.10: A comparison of the mean values of Acceleration Impulse for

posture (Each posture bar n=16). Al1 error bars represent the standard

error. .

Figure 4.1 1 : A comparison of the mean TTPK Acceleration values for the

posture & gender interaction (Each gender value for palmer & ulnar n=8).

A11 error bars represent the standard enor. .

. . . Xl l l

Chapter 1: INTRODUCTION

1.1 BACKGROUND

Upper extremity work related musculoskeletal disorders are significant problems for

empIoyers and workers in many industries. Of al1 lost time clairns filed to the W S & B in 1997,

the upper extremity comprised 24.2%, coming second to back injuries (WS&IB, 1998). It is

estimated that 20 million laborers work on assembly lines or at jobs that necessitate these

continuous and repetitive upper extremity motions (Armstrong et al., 1986). As a result, the past

decade has seen a dramatic increase in the incidence of upper extremity repetitive strain disorders

(Nelson et al.. 1992; Siiverstein et al., 1987). As biomechanical stresses exceed the physiologic

repair capability of the tissue, continuous damage can result. Repetitive, sustained or forcefûl

motions occumng over time act to compromise the integrity or functioning of soft tissue,

producinç inflammation of tendons or compression of peripheral nerves (Armstrong, 1986;

Si lverstein et al., 1986). As these stmctures experience micro traumatic damage, the worker is

placed at greater risk of additional injuries and the development of chronic problems.

Previous research has identified possible nsk factors for upper extremity disorders.

Through epidemiological (Armstrong et al., 1989; Silverstein et al., 1987; Silverstein et al., 1987),

biomechanical (Goldstein et al., 1987; Keir et al., 1997; Moore et al., 1991), and psychophysical

studies (Potvin & Chiang, 1998; Snook et al., 1995), there is a common consensus that repetition,

force, and awkward postures constitute key factors in the development of upper limb cumulative

trauma disorders (CTD's). It is further concluded that as these factors appear together the

likelihood of injury increases (Armstrong et al., 1987; Moore et al., 1991). Work done by

Si l verstein et al., ( 1 986), have found similar resul ts by comparing four exposure groups including:

1 ) Iow force low repetition; 2) low force high repetition; 3) high force low repetition; and 4) high

force high repetition. They found that high forces and high repetitiveness were associated with

CTD's and that there presence, in combination, substantially increased the magnitude of its

potential risk.

Along with highly repetitive and forceful motions, industrial tasks can also involve the use

of repeated hand impacts. Trim and assembly plants require impacts on parts, which involve high

forces causing shock (vibration) and high stresses over the palmar and ulnar side of the hand.

Mc Atamney and Corlett (1 993) have identified shock and rapid force increases as specific

ergonomie nsk factors by including this in their rapid upper limb assessrnent (RULA) method.

Armstrong ( 1983) and Snook et al. (1995) have identified these rapid force increases around the

wrist (torque) to be associated with a number of hand and wrist injuries.

Biomechmical impact studies have focused mainIy on crash testing, racket sports and

mnning. The \pariables which determine impact forces are: velocity, effective mass, area of

contact. and the material damping properties present (Nigg, 1983). Studies have used variables

such as force. acceleration, rate of load, and impulse to determine impact severity as weil as

measuring the darnping capabilities of materials (Lafortune and Lake, 1995; Nigg, 1986). Upper

limb injuries in tennis have been associated with the impact between the racket and bal1 and the

vibrations that are transferred to the arm (Berhang et al., 1987; Hatze, 1992; Hennig et al., 1992).

Segessor (1 985) suggests that tennis racket oscillations (at the palrn of the hand), in the range of

80-200 Hz, are likely to contribute to the development of tennis elbow. Running studies have also

2

suggested that the development of these shock waves upon impact is responsible for degenerative

changes in joints and articular cartilage (Lafortune et al., 1996). This is supported by Radin

( 1 973). and James & Jones (1990), who revealed that repeated impulsive loading c m produce

degenerative changes in biological tissues. To lower impact forces and absorb energy, running

shoes have incorporated different material properties (Nigg et al., 1987). Unlike running studies,

impact studies of the upper limb within the industrial setting are rather limited. Although efforts

have been made to reduce impact loads within industry through job redesign or the use of impact

glo~res. information is still Iacking regarding acceptable impact forces and how these impulsive

forces affect the upper limb.

Although previous research has shown high repetition, high force, and impact loading to

be key risks and highly correlated with CTD's, a major probiem exists as these factors are usually

looked at separately outside the industrial setting. Difficulty lies in attempting to study a number

of these factors together as they develop naturally within the industrial setting. Usine a

psychophysical methodology allows the estimation of safe levels of physical exertion under

numerous conditions.

Psychophysics is a well-established branch of psychology that is concerned with the

relationship between sensations and their physical stimuli (Gescheider, 1985; Snook, 1970). This

merhodology relies on the assumption that individuals can identify work conditions that are safe

for them based on the integration of biomechanical and physiological sensory feedback.

Psychophysical critena for acceptable loads in industry have been pioneered by Snook (1 969).

Snook (1 970). Ayoub (1978), Snook (1978), and Snook and Ciriello (1991) have used

psychophysics to determine maximal weights and forces for various litting, lowering, pushing,

3

pulIing, and canying tasks.

More recently, psychophysical methods have also been used to set acceptable exposure

lirnits for the upper limbs. Armstrong et al. (1989) were one of the fïrsts to do this by correlating

subjective assessments with objective measurements of hand tools used in automobile assembly.

Psychopliysics has also been used to determine acceptable fiequencies for drilling in various wrist

postures (Davis & Fernandez, 1994; Kim & Fernandez, 1993), varying applied forces (Kim &

Femandez. 1993) as well as gripping with various forces and duration's (Dahaland & Fernandez,

1993). Also. Snook et al. (1995) have used psychophysics to set guidelines for repetitive wrist

flexion and extension exertions.

Most recently, Potvin and Chiang (1998) were the first to use a psychophysical method to

determine acceptable limits for hand impacts of a vertical surface at selected fiequencies and

locations for males and fernales. It was concluded that an increase in impact frequency resulted in

a sisnificant decrease in acceptable levels of force, hand acceleration and impulse. Impact

location (palm) failed to show a significant effect within al1 four-impact locations relative to the

subject's bodies (high near, high far, low near, low far). Males in the study demonstrated a trend

towards accepting impacts with higher peak forces, impulse, load rates and lower times to peak

than fernales. Thus males appear to tolerate more severe impacts than fernales. An important

finding was that the within subject coefficients of variation were lowest for the impulse variable.

This suggests that the subjects controlled this variable to determine safe loads. Impact tolerance

was observed to range fiom 181 to 259 N for peak force and 2.53 to 3.52 Ns for force impulse for

impacts with the bare palm.

To date only Potvin & Chiang (1998) have investigated the feasibility of using a

4

psychophysical methodology to detemine maximum acceptable impact forces for various

repetitive hand motions and postures. Further analysis is needed to inciude the implementation of

impact gIoves as well as other impact locations on the hand during door trim installation. Hand

impacts within industry have involved the palmer and ulnar sides of the hand. Impact gloves have

been used by industry as a method to reduce demands. However, little is known about how the use

of impact gloves or impact locations on the hand affects performance and tolerance. Still, many

assembly Iine tasks continue to involve repetitive hand motions, high forces and impacts to the

upper limb. Adopting a psychophysical methodology allows the opportunity to implement safety

standards in industry were multiple factors can be looked at simultaneously.

1.2 PURPOSE

The purpose of this study is to expand on the findings of Potvin and Chiang (1 998) using a

psychophysical methodology to establish acceptable impact seventy limits for impacts of a

vertical surface using a simulated door trim panel installation task with different hand impact

postures with and without the use of impact gloves.

1.3 HYPOTHESES

I t is hypothesized that the use of impact gloves would result in a decrease in the severity of

the impact loading on the hand and upper lirnb. It is expected that the impact glove will act as an

energy absorbing mechanism, which will defom before the hand and thus decrease the overall

force peaks and disp lace this force over a longer period. It is also expected that this will result in

an increase in the level of extemal impact tolerated by the individuals. It is speculated that males

5

\vil1 accept impact severity values much greater than fernales. It is also speculated that impact

location (palmedulnar side) on the hand will have an effect on tolerance values. Within a

previous study by Potvin & Chiang (1998) al1 subjects chose to impact the device using the

palmer surface. It is assumed that the subjects used a posture tbat is most enicient for the task and

\vil1 the11 result in higher impact peaks and tolerance than ulnar impacts.

1.3 LI3IITATIONS

The lirni tations of the psychophysical methodology and the assumptions made must be

recognized before conclusions c m be accepted. Subjects require training to do this reliably and

errors can be made. It is possible that subjects may choose limits that they feel are appropriate but

may in fact cause physiological fatigue or biomechmical damage. Another problem is that one

can only generalize over a limited population.

1.5 DEFINITION OF TERMS

PK Force: first peak force, corresponding to the highest reaction force during the impact phase

TTPK Force: time of occwrence of PK Force afier hand strike

LR Force: rate of loading, caIculated as the siope of the reaction force-time curve

Force Impulse: total impulse during contact, calculated as the area under the force-time cuwe

PK Accel.: first peak acceleration, corresponding to the highest reaction acceleration dunng the impact phase

TTPK .4ccel.: time of occurrence of PK Accel. afier hand strike

LR k c e l . : rate of loading calculated as the dope of the reaction acceleration-time curve

Accel. Impulse: total impulse dunng contact calculated as the area under the acceleration-time cunre

Tolerance Lirnit Value (TLV): the maximal tolerance Iimit value found to be acceptable by 75% of the population

Impact force: the initial transient peak in the reaction force delivered to the hand as a result of the collisioi~ between the hand and the impact plate

Impact Severity: the magnitude of the impact acceleration delivered to the hand at hand strike

Chapter 2: LITERATURE REVIEW

2.1 UPPER EXTREMITY DISORDER

Work related chronic musculoskeleta1 disorders (or cumulative trauma disorders) are

recognized as major occupational health problems. Disorders such as carpal tunnel syndrome,

tendinitis. tenosynovitis, epicondylitis, chronic muscle strain or degenerative joint diseases have

been linked to a number of jobs which involve high repetitions, high forces, and mechanical stress

(Hi-gs et al.. 1992; Ranny et al., 1995; Silverstein et al., 1987).

The determination of health outcornes is rather difficult, as there are many potential sites

of injury. Within each disorder there is a range of severities and these disorders are frequently

episodic in nature. In spite of such complications, disorders of the upper extremity are

categorized as being reIated to tendons, muscles, nerves, or neurovascular involvement

(Son-imerich et al., 1993). The involvements of these disorders have been identified to affect the

upper limb.

1 ) Slioulder. A m & Elbow

Recent studies have shown the prevalence of shoulder pain syndromes to be elevated in

many working populations (Sommerich et al., 1993). Injury or fatigue of the rotator cuff muscles

can lead to altered mechanics and load distributions around the shoulder which can increase the

chance of additional tissue darnage (Whiting & Zemicke, 1998). Tendon related disorders of the

shoulder have included rotator cuff tendinitis, calcific tendinitis, bicipital tendinitis, or tendon tear

(Sommerich et al ., 1 993). Bicipital tendinitis can occur where tendemess is experienced in the

bicipital groove due to excessive elbow flexion and foream supination (Hagberg, 1987) or when

the elbon. and a m are extended and the forearm is supinated (Cailliet, 1981). The highly

repetitive nature of tasks in tendon studies have s h o w a progressive deformation (hysteresis)

mith cyclic loading which can lead to micro-trauma and ovenise (Norkin, & Frankel, 1989).

The posture required to secure the door trim panel is sirnilar to the posture of the tennis

forehand. So fi tissue and bony injuries around the elbow are very cornmon and usually related to

overuse (Field & Savoie, 1997). Lateral epicondylitis, media1 epicondylitis, media1 pain related to

ulnar n e n e injury. or valgus elbow instability can account for symptoms of elbow injury. Also,

O lder individuals ofien develop symptoms related to degenerative changes within the joint itself.

Lateral epicondylitis is extremely comrnon, with over 50% of tennis players experiencing

s ymptoms at some time or another (Maylack, 1988; Whiting & Zernicke, 1998). The excessive

use of ~vr is t extensor musculature is clearly associated with its development. Repetitive micro

traumatic injury at the extensor origin probably leads to a micro-tex, which repairs itself, but may

result in mucinoid degeneration and leads to a failure of the tendon over time (Field, & Savoie,

1997). Medial epicondylitis, which is less comrnon, occurs as wnst flexion and pronation is

resisted. Golfers and tennis piayers are comrnonly affected as a result of the repetitive valgus

stress placed on the sofi tissue of the media1 elbow.

The actions found in door trim installation cm place tremendous stress on elbow joint

stabilizers. The application of valgus stresses to the anterior bundle of the medial ulnar collateral

ligament can cause injury or insufficiency (Field & Savoie, 1997). An important secondary

stabilizer of the elbow, when media1 ulnar collateral ligament insufficiency is present, is the

9

articular geometry of the joint itself. In the presence of a disrupted media1 ulnar collateral

ligament. abnormal stress on the articular surfaces leads to injury and degenerative changes with

osteophyte formation that c. produce media1 elbow symptoms (Field & Savoie, 1997; Norkin &

Frankel. 1989). Darnage to ligamentous restraints leads to the transfer of significant stresses to

bony articulations. In addition, this may contribute to lateral elbow pain through increased

radiocapitellar joint compression that occurs with valgus stress and as a resuIt of asynchronous

firing of the wrist extensor musculature (Field, & Savoie, 1997).

It is unlikely that this type of injury will occur due to the fact that the elbow, during this

action in the door panel trim assembly, will not experience the large moments around the joint as

seen in the tennis forehand, or golf swing. However due to the repetitive loading and valgus

stresses placed on the joint these symptoms and disorders shouId not be overlooked because

continued loading worsens the microscopie damage and eventually leads to syrnptomatic tissue

invol\.ernent in the fonn of inflammation, inflexibility, and tissue weakness (Whiting, & Zernicke,

r 99s).

2 ) The Wrist and Hand

Injuries from repeated tissue stress can also affect the wrist and hand. One of the most

debi li tating chronic disorders is carpal tunnel syndrome, a condition charactenzed by swelling

within the carpal tunnel, which causes compression on the median nerve or blood vessels running

through the tunnel. The inextensible borders formed by the carpal bones and the flexor

retinaculum preclude an increase in tunnel size. Inflammation and edema in response to repeated

loading compress neurovascular tissues and compromises mobility (Whiting, & Zemicke, 1998).

IO

The development of carpal tunnel syndrome has been linked to numerous nsk factors including:

forceful exertions, repetitive or prolonged activities, awkward postures, localized contact stress

and vibration (Armstrong et al., 1987; Moore, & Garg, 1995; Ross, 1994; Silverstein et al., 1987).

The development of carpal tunnel syndrome is unlikely during hand impacts but compression of

the hand during impacts may affect surrounding nerves and blood vessels restricting blood flow to

surrounding musculature and tendons leading to micro-trauma. However, Gelberan et al. (198 1)

ha\.e implicated vascular insufficiency as a major cause of carpal tunnel syndrome. Also, ulnar

nenqe compression at the wrist has been associated with chronic repetitive trauma to the

hypotllenar eminence (Moneim, 1992; Zirnmerman et al., 1992). Mechanical compression of the

liypothenar erninence occurs during the task of seating door trim panels which places nerves and

ansries to direct compression affecting the supply of blood and nutrïents to surrounding tissue.

Tendons fulfil a load transmitting role, but along with this main load bearing function,

tendons satisfy both kinematic requirements (they must be flexible to bend at joints and ensure

that the musde is always loaded in a traction mode) and darnping requirements (they absorb

sudden shocks, thus limiting possible damage to muscles caused by them)(Pradas Br Calleja,

1 990). S tudies have demonstrated that tendons possess viscoelastic properties (GoIdstein et al .,

1987: Hooley et al.. 1980; rada as, & Calleja, 1990; Schwerdt et al., 1980). During cyclic loading

mechanical hysteresis occurs. Within hysteresis, energy is supplied to stretch the tendon, but

some of this energy is dissipated by causing the flow of fluid within the ground substance. As this

occurs energy is lost creating hysteresis. Relaxation then does not follow the same path requiring

tinie to get back to its normal functioning. If time is not sufficient the load bearing ability of the

tendon is no longer as effective during the sarne loads.

11

In addition to mechanical responses, tendons also respond physiologically. Physiologic

responses include metabolic, circulatory, and adaptive changes. Gray (1 893) and de Querivain

( 1895) were among the earliest to identiQ these changes. Howard (1 937) reported jelly like

changes in the tendon-muscle junction, even when then the tendons and sheaths appeared normal

to the naked eye. Typical findings include: thickening, proliferation of fibrocytes and fibrous

comective tissue, destruction of synovial membranes and adhesions (Armstrong et al., 1984;

PliaIen. 1966). Armstrong et al. (1984) have f o n d proliferation of fibrous comective tissue to be

oreater on the palrnar and dorsal sides of the finger flexor tendons where compressive forces are - greatest. -

The mechanism of these changes is unclear, but it is speculated that the occlusion of blood

flow and the deprivation of nutrients play a prominent role (Armstrong et al., 1987). The nutrient

patliway involves both bulk flow and diffiision. The ability to move these nutrients through

diffusion requires a concentration gradient behveen the tendon and synovium, which is dependent

on the circulation available (Manske et al., 1985). The occlusion of blood flow (as a result of

compression of the tendon against adjacent surfaces), the thickening of tendon sheaths or

increased diffusion distances would al1 act to deprive the flow of nutrients. The level of this

deprivation is affected by the intensity of exertion, the duration, and the fiequency of the exertion

(Armstrong et. al., 1987). Although tendons may be better suited to bear these forces, other

tissues in the surrounding area such as blood vessels and nerves are not. The result is that some

tissues can endure more trauma than others, but both tissues do have limits and damage will ensue

i f time for recovery is insufficient.

Axial loading of the hand can also result in degenerative changes of the carpal bones.

12

Cartilage reduces stresses applied to bones by increasing the area of contact between the

articulating surfaces and reduces bone on bone Wear. However, fatigue Wear of bearing surfaces

can occur fiom the accumulation of rnicroscopic damage within the bearing material under

repetitive loading. Failure can occur with the repeated application of high loads over short

penods or even low loads over an extended period of time (Norkin, & Frankel, 1989). Applied

loads cause pressure gradients to occur in the interstitial fluid, and these variations in pressure

cause fl uid to fiow through and out of the matrix. Damage to articular cartilage, as a result of

cyclic loading, c m dismpt the normal load canying ability of the tissue and thus the normal

lubricating process operating in the joint. The compressive stiflhess and resistance of cartilage

depends upon the water and proteoglycon content of the tissue (Norkin, & Frankel, 1989). It is

hypothesized that failure progression may be accounted for by the magnitude of the stress, and the

total iiumber of stress peaks sustained, which may alter the articular matrix and normal load

canying ability (Norkin & Frankel, 1989).

2.2 AS.4TOhIY

The anatomy of the upper extremity associated with palmar and ulnar side hand impacts

for the si~nulared task of door trim panel installation will include; the lower a m , as well as the

wrist and hand. Anatomy will be limited to pertinent information concerning the muscles, nenres,

artenes and bones that are associated with the movements performed in simulated door tnm panel

installation.

1 ) Impact A m Position and Action

Industrial door trim installation requires the worker to use their a m to impact door trim

panels. During installation, impacts are perfonned using two different postures. Paimar impacts

require the a m to be around 90 degrees (Humerus & radius/ulna) of flexion were force is applied

tluough interna1 rotation of the m. During impacts with the ulnar side of the hand the arm is

slightly flesed at the shoulder with the elbow at 90 degrees of flexion with forearm pronation,

were force is applied by extending the m. The elbow joint is reinforced by a number of

ligaments and muscles that cross the elbow. This provides stability within the joint. Injury

usually affects the tendonous attachments of muscles near the media1 and lateral aspects of the

elbow that are often imtated and inflamed by repetitive stresses (Anderson, & Hall, 1995).

Table 2.1 : Movement of the upper a m during door trim installation. The intemal rotators, elbow flexors/extensors and pronators of the arm.

Elbotv Flexion

Interna1 Rotation

1 ) Brachialis 2) Brachioradialis 3) Biceps 4) Extensor Carpi Radialis

1) Subscapularis 2) Pectoralis Major 3) Latissimus Dorsi 4) Deltoid (Anterior Portion)

1 Elbow Extension 1 1) Triceps

Pronation 1 ) Pronator Quadratus 2) Pronator Teres

2) The Wrist and Hand

During repetitive impacts during door trim installation the hand is subject to direct

compression. This places the hand and its underlying tissue under compression, which can lead to

desenerative changes and micro traumatic damage. Muscles, tendons, nerves, and arteries c m be

affected. Figures 2.1, 2.2 and 2.3 illustrate the sections of the hand that are repeatedly exposed to

compressive forces and trauma.

Median nCrve

xor landon9

Fisure 2.1 : The structure of the carpal tunnel and hand. Neurovascular structures, including the median nerve, ulnar nerve, and ulnar artery pass through the carpal tunnel bounded by the flexor retinaculum and the carpal bones. Compression due to impacts to the ulnar and palmar side of the hand can effect these under lying tissues.

(Norkin, & Frankle, 1989) Figure 2.2: Carpal bones of the hand. Compression due to impact c m create degenerative changes with the wrist joint.

(Anderson, & Hail, 1995) Figure 2.3: During impacts there are many muscles that are of concern within the hand. Duriiig industrial door trim seating tasks impacts are perfoxmed using the palm or the ulnar side of the hand. During these motions the abductor pollicus brevis, opponens pollicis, flexor pollicus brevis, opponens digiti minimi, palmaris brevis, abductor digiti

minimi, and the flexor digiti rninimi brevis are under constant mechanical stress.

16

The existence of a proximal and a mid-carpal joint in the wrist creates a double hinged

system. wliich c m provide inherent stability of the wrist. With vimially no musculature on the

carpus to provide dynamic stability, the compressive forces are taken up by articulating surfaces

and its ligarnentous constraints. A fine balance of extrinsic and intrinsic musculature provides

the dynaniic stability of the wrist. The arrangement of digital and wrist extensor and flexor

systems around the wrist allows stability to be maintained. However, these muscle activities

place more compressive and shear forces on the carpal bones. The wrist is not a single joint, but

rather a group of articulations that includes the distal radioulnar, radiocarpal, and intercarpal

joints. MuscIes of the f o r e m prharily control wrist motion with assistance fiom intrinsic

muscles of the hand. The distal tendons of most flexor muscles of the forearm pass along the

ventral aspect of the wrist, .where they are held firmly in place by the flexor retinaculum (thick

facial sheath). These tendons along with neurovascular stnictures pass through the carpal tunnel

formed by the carpal bones and the flexor retinaculum (Figure 2.1). The distal tendons of the

estensors are secured similarly between the carpal bones and the extensor retinaculum.

The carpal bones are also exposed to repetitive loads, which c m fatigue the articulas

surfaces causing micro traumatic damage. Failure can occur with the repeated application of

high loads over a relatively short period or with the repetition of low loads over an extended

period, even if the magnitudes are much lower than the materials ultimate strength (Norkin, &

Frankel, 1989). Possible mechanisms of injury have included; insufficient recovery, impairment

of self-lubncating ability or changes in rnatrix composition (Norkin & Frankel, 1989). It is

hypotliesized that failure progression relates to the magnitude of the imposed stress and the total

number of sustained stress peaks.

17

3 ) Nenres and Blood Vessels

The medi an, ulnar, and radial nerves are major terminal branches of the brachial plexus

that provide motor and sensory infoxmation to the wrist and hand. The median nerve supplies the

ma-jonty of the fiexor muscles of the wrist and hand, as well as the intrinsic flexor muscles on the

radial side of the palm. ï h e radial and uinar nerves merge in the palrn to form the superficial and

deep palmar arches.

The major vessels supplying the muscles of the wrïst and hand are the radial and ulnar

arteries. The radial artery supplies the muscles on the radial side of the forearm, as well as the

thumb and index finger. The radial artery is superficial on the palmar side of the wnst where it

may be sulnerable to compression and mechanical stress. The ulnar artery spans a major branch

knokvn as the cornmon interosseous artery, which divides into anterior and posterior arteries. The

anterior branch supplies the deep extrinsic flexor muscles, and the posterior branch supplies the

extensor muscles of the forearm. Digital arteries branch fiom the palmar arches to supply the

tingers that can also be affected during repetitive impact or compression. Using the ulnar side of

the hand places the digital gtenes, ulnar nerve and ulnar artery in a place to be affected by

compression and mechanical stress during impact.

2.3 SHOCK ATTENUATION

The body is subjected to impact during many activities. Such loading can occur during

running and racket sports but c m also occur during occupational tasks. However limited

information is present on these types of impacts as they pertain to the industrial setting but with

the sport research available it may provide some hsight into this issue.

18

During heel toe ruming, a typical ground reaction force exhibits a hjgh frequency

impact peak in the first part of the support phase. ïh is peak reaches a maximum of 2-3 times

that of body weight in the first 10-20 ms when barefoot (Miller, 1990; Nigg, 1988) and in the

first 15-35 ms when wearing running shoes (Nigg, 1986). Looking at a psychophysical hand

impact study perforrned by Potvin & Chiang (1998) average peak forces were 644.9 N over a

range of impact frequencies. These impacts occur at rates similar to barefoot studies (peaks

\vithinlU ms) (Potvin & Chiang, 1998)- Munro et ai (1987) measured vertical ground reaction

forces during - initial impact in running at 3.5 rn/s and found impact values to reach peaks of 1270

N in 30 ms. Although, hand impact forces may only be half of that found by Munro (I987), both

studies have shown that impacts using the hand or foot are subject to both high force magnitudes

and Iiigh rates of loading (Nigg, 1986; Potvin & Chiang, 1998). Once contact is made with the

surface of an irnmovable object (ground, door trim etc), rapid deceleration occurs transmitting

shock\va\.es through the rnusculoskeletal system (Demck et al., 1998). Through the use of skin

or bone mounted accelerometers, measurement of these shockwaves can be made.

Impact loading of the human musculoskeletal system has the potential to cause injury.

Researchers have speculated that physical activity of this nature may produce overloading effects

if the forces acting on specific structures are larger then their attenuating abilities (Lafortune and

Lake. 1995; Njgg, 1988). The periodic tension placed on soft tissues due to the high loading

rates is assumed to be comected to injury (Nigg, 1987). Even under normal physiological

conditions the chronic, repetitive application of shock waves to the locomotor system will tend to

cause a slow and progressive weakening of the bodies natural shock absorbers (Nigg, 1988;

Radin, 1972). Radin et al. (1973) have shown that the high impact forces associated with heal

19

strike may damage articular cartilage as well as cause degenerative joint disease. Also, Collins

and h l i t t l e (1 989) have reported a relationship between heel strike impulsive loads and the

development of injuries. Studies have documented that this is a result of possible imbalances

existing between the loads applied to the musculoskeletal system and load capacity of the sofi

tissue and bones (Clement et al. 1981; James et al, 1978; McKenUe et al. 1985; Nigg, 1988). To

prevent this damage impacts must be attenuated using active and passive mechanisms.

External mechanisms Iike a cushioning interface or the intemal mechanisms of the

elasticity of bone and sot? tissue, cartilage and synovial fluid are al1 responsible for the passive

mechanisms of shock attenuation. Tenned the "naturaI shock absorbers", these mechanisms are

relatively more important at the beginning of the impact peak when they help to attenuate shock

at impact (Radin et al., 1973; Voloshin and Wosk, 1982). Synovial fluid and articular cartilage

are important for decreasing the effects of impact loading but, due to their thin layers, they have

mi nima1 e ffects during shock attenuation (Radin and Paul, 1 97 1). Experimental evidence has

suggested that bone defonnation and muscle Iengthening under tension, associated with joint

motion and soft tissue, play the major roles in attenuating peak dynarnic force. Due to their

mass and surface area necessary, deformations c m occur which are most effective for shock

attenuation (Radin and Paul, 1970).

Relative contributions of bone and soft tissue have been measured. Paul et al. (1978)

induced three types of impulsive loads to splinted tibias of white New Zealand rabbits. The

loads n-ere very similar but variations were made in the fiequency components. The result

revealed very slight attenuation between 3-18 Hz with a 3 Hz application fiequency. However,

attenuation increased dramatically when the application fiequency was raised. Approximately

20

S0% atrenuation was achieved at 60 Hz, increasing to almost total attenuation at 360 Hz. When

impulses were delivered at 500 Hz - 3000 Hz, complete attenuation occurred. The precise

contribution of sofi tissue and bone was more prominent at the higher fiequencies, and contribute

minimally to the lower fiequencies. The heel pad was found to contribute most significantly at

al1 frequencies reducing peak dynamic forces by 20 - 28%. However, no method has yet been

devised that is capable of measuring heel pad properties in vivo without artefacts, due to the

presence of the leg (Ker et ai., 1995). Values of attenuation fkom in v im tests have been found

to range from 30% (Bennet & Ker, 1990) to almost 50%. In vivo testing shows larger

discrepancies of shock attenuation. These values have been measured to be around 7595%

(Aer-ts & D e Clercq, 1993; Cavanagh et. al. 1984). Although the damping property of the foot

lieel pad is unclear, it is still agreed that it serves to Iower impact peaks. The mechanical

properties of the palmar surface or ulnar side of the hand have not yet been determined. but it is

speculated tliat it shares similar properties with the heel pad in ninning (Robbins et al., 1989).

Hennig et al. ( 1992) have shown that peak-to-peak acceleration at the wrist is approximately 4.5

times higher as compared with the elbow accelerations in the tennis forehand. The rectified

acceleration integrals at the elbow are less than 26% that at the wrist. These findings show

similar shock attenuation values as those results found on lower limbs.

Active mechanisms of shock attenuation include proprioception, joint position and

muscle tone. These mechanisms are not able to contribute to the attenuation of shock until the

body has had sufficient time to react to the afferent information. Although much debate exists as

to the exact reaction time of muscle, it is generally agreed that the short duration of the impact

peak means it evokes a purely passive response fiom the body (Nigg, 1982; Nigg, 1983). This is

21

due to the fact that the musculoskeletal system is not quick enough to react and respond within

this shon time frame (10-35 ms) for the rise in peak force. Studies investigating the latency of

voluntary and reflex contractions have concluded that conscious control has too long a latency

period to be an influence dunng the impact phase (Viitasola et al. 1980). Funher findings by

Gottlieb et al. ( 1979) showed that significant changes in muscular moments, due to stretch

reflexes, do not seem to occur within the first 100 ms after stretch. Nigg (1 988) classified loads

that reached m~ximum peaks within 50 ms as passive, indicating that the brief duration of the

impulses does not allow any reactive damping to occur by surrounding musculature.

In spite of the absence of possible reflex contributions to impact attenuation, there is a

possibi lity that muscle pre-activation through a feed forward mechanism, can allow muscle

contraction to contribute to shock attenuation. Knudson, (1991) have shown that the hypothenar

muscles of the hand increased activation 50 ms before bal1 impact in the tennis forehand. It is

typically assumed thar an increase of muscular CO-activation is coincident with an increase in

joint stiffness, which then causes impact force to increase. Although muscular activation affects

joint stiffiiess. and impact forces, it is agreed that muscle contraction absorbs considerable

ainounts of energy (Anderson & Hall, 1995).

I t is well known that fatigue of the muscles affects the performance and finctioning of

the body. Muscles have the ability to lower the bending stress placed on bone and attenuate the

peak dynamic loads of impact to prevent musculoskeletal tissue damage. Studies have showrn

that the ability of the human musculoskeletal system ta protect itself from overload is hampered

by muscle fatigue (Verbitsky et al., 1998). This loss of protection may be manifested in

increased shock wave amplitudes.

2.3 IMPACT PROTECTION

Impact protection is common within professional sport. Equiprnent is designed to provide

effective protection within which a sport is confined. The physical needs of a particuiar sport

deternline the protection required. As seen within many tasks that involve impact loading, there

iç potential to cause injury. Previous studies have determined that injury occurs as a result of the

magnitude and the type of loading present (Bishop, 1976,; Nigg, 1983). Running, helmet, and

crash testing research has provided evidence to irnplicate impact forces as a cause of injurious

effects on the body (Bishop, 1976; Lafortune and Lake, 1995; Nigg, 1983).

To lower these forces during impact, materials have been developed to attenuate and /or

prolong the application rate of the impact force helping to prevent the bodies' natural shock

absorbers from being overloaded. The determination of effective equipment attenuating abilities

reqiiires many mechanical variables to be rneasured dunng impact. These variables incfude

acceleration, rate of onset, force, kinetic energy, momentum, and impulse (Bishop, 1976;

La fortune, & Lake, 1995). Through the use of these variables many researchers have been able

to delineate the mechanisms of impact or impulsive load damage.

These measures have allowed researchers to evaluate the mechanical properties of tissues,

determine tolerance limits, as well as evaluate the effectiveness of protective equipment. The

first effective tolerance curve (acceleration-time) was provided by Gurdijan et al ( 1 966) which

was called the Wayne State Tolerance Curve (WSTC). This curve uses linear skull fracture data

often associated with moderate to severe concussions, as an injury critenon. This is a boundary

curve, were head blows of a magnitude and duration above a predeterrnined value considered

intolerable (from testing) is determined dangerous while those that fa11 befow this value are

23

tolerable. The Gadd Severity Index (GSI) later replaced the WSTC. The WSTC was

inapplicable at either extremes of the curve and portrays an average acceleration as a fwiction of

pulse duration. By taking the log-log plot of the WSTC, and then approximating the slope

betn-een 4-50 ms with a straight line a more accurate index was created (GSI). The GSI was a

wei$ted impulse criterion and a GSI value of 1500 or more was considered dangerous.

The designs of specific helmets have adopted this criterion to determine effective helmet

design and impact attenuation. Studies by Bishop (1976) allowed the determination of effective

helmet design. Automotive industries have also used this criterion dunng vehicle impacts. Other

areas ha\,e focused on shoe and playing surface design to lower the nurnerous injuries occurring

in running and hard court sports. Many studies have shown that hi& impact forces occurring

o\.er a short penod of time cause injury. This has resulted in the design of equipment to decrease

these loads that act on the body. However, when considenng the hand during impacts little

infom~ation is available.

Indi~strial tasks expose the unprotected hand to moderate to high velocity impacts, to set

and seat automotive parts into place. Dunng these industrial tasks the hand begins to decelerate

coming to rest in some finite time interval during which the hand undergoes deformation due to

the force and pressure per unit area created over the paIm of the hand. However, if a piece of

energy absorbing matenal is placed between the hand and the contact surface, the material will

cnislu'defom rather than the hand or will act to lirnit its effects on the hand. This allows the

hand to decelerate through a greater distance. The degree of protection afforded depends upon

the distance through which the matenal cm be deformed before "bottoming out" (Bishop, 1976).

Once bottomed out, the hand remains in motion but at an acceleration that is reduced.

24

The design and selection of protective equipment is based on the optimal Ievel of impact

intensity afforded by the given thickness, density, and temperature of the energy absorbing

material (Anderson, & Hall, 1995). Soft, low-density material is light and cornfortable to Wear,

but is only effective at low levels of impact intensity. In contrast fimer, hi&-density material of

the same thickness tends to be less corr~fortable, offers less cushioning of low level impact, but

can absorb more energy by deformation and thus, transfers less stress to the body. Another

factor to consider in energy absorbing matenal is resilience to impact forces. HighIy resilient

materials regain their shape after impact and are commonly used over areas subjected to repeated

impact. Low resilient materials or slow recovery resilient matenal offers the best protection, and

is used over areas subjected to one time impacts (Anderson, & Hall, 1995).

The selection of impact _eloves by industry has focused on the use of sorbothane to

protect the hand dunng these impacts. Sorbothane is a new visco-elastic material that provides

nmsimurn comfort and protection during various loading conditions. Sorbothanes unique liquid

solid properties allow it to simultaneously absorb shock and isolate vibration even at high

frequency ratios (Sorbothane online, 1998). Sorbothane allows high darnping in a polymer which

allows the reduction of the force peak by distributing it over a longer t h e h e . Sorbothane

Inc. testing has shown reductions in impact forces of up to 80% bnnging the mass to rest slowly,

facilitating better protection (Sorbothane Online, 1998). Research has shown that even after two

million compressions there were no significant changes in sorbothane's physical characteristics

(IEM Medical Technologies Inc., 1998).

(Sorbothane Inc., 1998) Figure 2.4: High darnping in a polymer reduces the impulse peak of a shock wave over a larger tirne fiame. Sorbothane functions to reduce the impact force and brings the mass to rest slowly, allowing better protection.

This unique nature allows it to maintain its high damping properties over cyclic loading

\vhich is necessary within industrial tnm installation. As shown in Figure 2.4 sorbothane has the

ability to lower the impact peaks and spread these forces over a longer penod of time. Previous

evidence has suggested that large force peak over small durations cause injury. Placing this

material between the impact surface and hand can effectively lower these peaks in tum

decreasing the forces reaching the hand limiting the chance of injury.

2.4 PSYCHOPHYSICS

Psychophysics involves the scientific study of the relation between stimulus and

sensation and therefore the problems of psychophysics constitute some of the most fundamental

problems of modem psychology (Gescheider, 1985). For a number of centuries psychologists

26

have sought to understand sensation, and the workings of the human mind.

In the early days of G.T Fechner (1 86O), psychophysics consisted primarily of

investigating the relationships between sensations in the psychological domain and the stimuli in

the physical domain (Gescheider, 1985). Central to psychophysics is the concept of sensory

tlireshold. Meaning that events must be stronger than some critical amount in order to be

consciously experienced. Absolute and difference thresholds are measures that go hand in hand

with psychophysics. The srnaIlest amount of stimuhs energy necessary to produce a sensation is

the absolute threshold. hé difference threshold is the amount of change in the stimulus to notice

a chanse. Psychology has used these t ems in psychophysics to investigate how the absolute and

difference thresholds change as some aspect of the stimulus (frequency, intensity, or position) is

systematically changed (Gescheider, 1985).

According to modem psychophysical theory, the strength of a sensation S is directly

related to the intensity of its physical stimulus 1 by means of a power fùnction: S=KP (Snook,

1985). The constant K is a function of the particular units of measurement used. When plotted

in log-log CO-ordinates. a straight line represents a power function, with the exponent n being

equal to the slope of the line. Exponents have been experimentally deterrnined for many types of

stimu 1 i (e-g. : 1 -3 for taste and 0.6 for loudness). More importantly, psychophysics has been

successfuIly used to provide quantitative descriptions of the capacities of the sensory modalities

and such information has been helpful in designing environments and equipment for people's

use. Of interest here is the perception of muscular effort and force, both of which have been

found to obey the power Iaw, both with an exponent of approximately 1.6 (Snook, 1985).

In more recent studies psychophysics has been used to detennine guidelines within

27

working environrnents. Psychophysics has gained approval al1 over the world. The National

Institute Of Safety and Health (NIOSH), the Occupational Safety and Health Association

(OSHA), the UK Health and Safety Commission, as well as Australia have approved

psychophysics as a major approach to develop ergonomic guidelines (Snook, 1983).

Snook and Irvine (1967) were the first to implernent guidelines for the evaluation and

design of manual handling tasks that were consistent with the workers capabilities and their

liniitations (Snook, 1991). The first guidelines were intended to assist hdustry in the control of

low back pain (LBP) through reductions in initial episodes, length of disability, and reoccurrence

(Snook. 1987). Using the relationship between sensations and their physical stimuli provides a

method that one can use to estimate safe exertion levels under a variety of conditions. The

primary advantage to the psychophysical approach is that it permits the realistic simulation of

industrial work, allowing aspects such as work space dimensions and task fkequencies to be

altered accordingly (Snook, 1985).

Psychophysical studies ailow the subject to manipulate one of the task variables (Weight,

force etc.) and al1 other variables are controlled. The subject then monitors his own feelings of

essrtion or fatigue, and adjusts the task accordingly. Only the individual subject can sense the

various strains associated with the task, and only they can integrate the sensory inputs into one

meâningful response. Subjects are instructed to work on an incentive basis, working as hard as

they codd without straining themselves or without becoming unusually tired, weakened,

overheated or out of breath (Snook, 1985).

The psychophysical approach has been used at the Liberty Mutual Research Center for

over 30 years (Ciriello and Snook, 1978; CirielIo and Snook, 1983; Snook et al., 1970; Snook,

28

197 1 ; Snook 1978; Snook and Cinello, 1974; Snook and b i n e , 1967). Snook (1970), Snook

(1978), Ayoub (1978) and Snook and Ciriello (1991) have used psychophysics to determine

maximal acceptable weights and forces for various lifting, lowering, pushing, pulling, and

can-ying tasks. In 1978, Snook established a Threshold Limit Value (TLV) at the 75th percentile

for both males and fernales. This TLV was based on insurance data indicating that a worker is

three times more susceptible to low back injury if performing a manual handling task that is

acceptable to Iess than 75% of the working population. This value has been accepted by NIOSH

~'110 have incorporated a psychophysical component when designing their lifting equations to

predict acceptable loads for 75% of women and 99% of men (MOSH, 1981).

Recently the psychophysical methodology has been used to set acceptable exposure Iimits

for the upper limbs. Armstrong et ai. (1989) were one of the first to do this by correlating

subjective assessments with objective measurements of hmd tools used in automobile assembly.

Psychophysics has also been used to determine maximum acceptable fiequencies of drilling

during different wis t postures (Davis and Femandez, 1994; Kim and Femandez, 1993) and

varying applied forces (Kim and Femandez, 1993) and of gripping under different conditions of

force and duration (Dahalan and Fernandez, 1993). Guidelines for receptive wnst flexion and

extension have also been determined by Snook et al. (1 995) using a psychophysical

methodolo~y.

Potvin and Chiang (1 998) were the first to use a psychophysical methodology to study

hand impact. Two studies were completed which required hand impacts to be perfomed to

simulate door trim panel installation where pushpins are driven through holes in the metal

doorframes. The first experiment was designed to determine the effect of impact frequency ( 2 , 5 ,

29

and 8/min.) on the acceptable impact severity. The second experiment was designed to

detemine the acceptable impact severity during a sirnulated door trim panel installation task

performed at 5 impactdmin.

The first experiment found that an increase in impact fiequency resulted in a significant

decrease in the acceptable levels of impact for peak force, load rate, and impulse. This is

consistent with previous lifting studies (Ayoub, 1978; Snook, 1995; Snook and Ciriello, 1991 ).

The greatest decrease occurred among 2 and 5 impacts per minute and subjects were not as

sensitil-e to frequency when going fiom 5 to 8 impacts per minute. Male subjects demonstrated

significailtly higher acceptable impulse levels and showed a trend towards accepting higher peak

forces when compared to fernales. Impulse and tirne to peak (CV=9%) and peak force

(CV= 14%) were the most reliable variables.

The second study used a fiequency of 5 impacts per minute with various postures relative

to the body to simulate door trim installation. Impact location, or arm position relative to the

body. failed to have a consistent effect on the acceptable impact seventies. P o ~ i n and Chiang

( 1998) concluded that an effect may have been obsenied if more extreme postures had been

studied. Significance was not found between genders for peak, time to peak, rate of loading and

impulse for both force and acceleration. Male subjects demonstrated a trend towards accepting

iriipacts npith higher peak forces, impulses, load rates, and lower time to peak than their female

counter parts. Thus males appear to tolerate more severe impacts. In spite of these trends the

differences between men and women were not significant.

Potvin and Chiang (1998) used variables to surnmarize components of the force and

acceleration time histones that were considered to be most directly related to the development of

30

a cumulative trauma disorder. It was assumed that the variables showing the greatest consistency

witliin subjects were the variables being controlled by the subjeets to select impact severity

limits. Impulse was the most repeatable variable over both experirnental conditions for force and

acceleration in study 1 and acceleration in study 2, with average coefficients of variation of 9%,

12%, and 14% respectively. This indicates good reliability. By making a cornparison between

peak force. time to peak, load rate and impulse, the average acceptable force impulse and time to

peak were found to be consistent with both studies. In addition, force impulse was found to have

the highest correlation (r=0.82) with the resistance setting being controlled by the subjects on the

simulation device. Peak forces in the first study averaged 61 4 N compared ta 235 N in study 2.

This indicates that the subjects were willing to accept relatively high impact forces on the force

plate but the forces did not reach these levels on the simulation device. This discrepancy may

indicate tliat peak force was not the variable subjects attended to when setting impact lirnits in

the second study. Based on these findings Potvin and Chiang (1998) concluded that force

impulse was the variable most likely being controlled by the subjects dunng each impact.

The TLV for impact loading was determined by pooling the data of both studies across al1

frequencies ranging from 2, 5, and 8 impactdmin. The fkquency dependent changes in tolerance

nrere based on a linear interpolation of the 2, 5, and 8hinute data of study 1. The limits ranged

from 18 1 N and 2.53 Ns (females, 8/min.) to 259 N and 3.52 Ns (males, 2/min.) for peak force

and force impulse variables respectively. The current study will attempt to extend these findings

by Potvin and Chiang (1 998) and determine tolerance limits for different hand impact postures

and protection conditions.

Chapter 3: METHODOLOGY

This chapter summarizes the experimental apparatus used and protocol employed for the

present study. The subjects gave wntten consent and were given monetary compensation for

their involvement. The University of Windsor Cornmittee for the Ethics of Experiments on

Humans approved the experimental procedures. The different sections included in this chapter,

cover espenmental conditions, subjects, instrumentation, protocol, data collection, data analysis,

and statistical analysis used in the present study.

3.1 EXPERIMENTAL CONDITIONS

Subjects were required to repeatedly strike a simulation devices in two selected postures.

In the first condition. subjects were to strike a simulation device with the palm @almar surface)

of their dominant hand in a horizontal plane (with a vertical surface) using the bare hand while

standing io the side of the device (Figure 3.1). The second posture required the use of the ulnar

side of the hand where subjects were to strike the simulation device plate again in a horizontal

plane (vertical surface) while standing in front of the device (Figure 3.2). Also within the palmer

and ulnar side impact conditions subjects were required to perform impacts with and without the

use of impact gloves.

A psychophysical methodology was used to detennine the acceptable impact severities

for each task. Subjects were instnicted to strike the simulation device as hard as they found

acceptable such that there would be no sign of discornfort, numbness, or injury after the session.

Impacts were performed at a rate of 5 per minute (perfonned at the subjects preferred pace within

eacli minute) as controlled by an audible metronome. Potvin & Chiang (1 998) found this

frequency to be the average rate of impacts performed per door trim panel installation. Training

sessions were used to familiarize the subjects with the psychophysical methodology and with the

consequences of the selected impact seventies. Subjects were required to perform 2 separate

training collection sessions, one of 120 minutes the first day and then another 120 minutes the

second day. In each session, they impacted the force plate 5 times per minute for al1 four

conditions (palmar handl bare hand, palmar handlsorbothane glove, ulnar side handhare hand,

ulnar side hand/sorbothane glove) for 30 minutes each in both days of training. A final session

of 1 SO minutes was also performed were each condition was perfomed for 15 minutes in the first

hour prior to the final 30 min each in the final collection. Collection occurred during the final

1 20 miniites leaving 30 minutes of collection for each posture. Within each session al1 impact

conditions n-ere randomly assigned to each subject. Also, each session was separated by at least

24 to 4s hours.

3.2 SL'BJECTS

Sisteen subjects (eight men and eight women), fiom a university population, participated

in the study. To be included, al1 subjects were screened for previous upper limb injuries prior to

selection and informed consent (Appendix A), and anthropometric values (Appendix B) were

obtained from each participant. Each subject was randomly assigned an order of the four

conditions (palmar side vs ulnar side, bare hand vs impact glove).

Figure 3.1 : A schematic illustration o f the palmer impact hand position.

Figure 3.2: A schematic illustration of the ulnar impact hand position.

3.3 PROTOCAL

Upon arriving at the laboratory, the subject read a description of the expenmental

procedure. Thereafter, any questions they had were answered in order to alleviate a11 concerns.

The written description of the experiment involved a final release that subjects read and signed.

This document was retained as proof of each subjects informed consent (Appendix A). Subjects

were required to perform two separate training sessions to familiarize themselves with the

methodology and monitoring their ability to determine acceptable limits for an 8-hr workday.

Data from each subject were collected in one session that lasted 180 minutes.

Basic information about the subject were gathered during the first training session. The

subject's name, age, height, md weight were recorded (Appendix B). An accelerometer was

attached to the subjects using a wrist brace, which was setup so the accelerometer could be

mounted on the back of the hand. Wiring from the accelerometer was strapped to the subject's

a m using velcro straps to keep them from getting in the way of collection.

Before collection began both the force transducer and accelerometer were calibrated to

ensure they were working properly. After verifjing that al1 equipment was ready for collection,

the subjects were familiarized and oriented with the impact motion and the sensation of impact.

This was accomplished through each training session, both of 120 minutes and another 60 minutes

before collection.

Subjects were instructed to determine the maximum impact load that was tolerable for

\vork during an 8-hr day. The subjects were required to simulate working on the assembly line

performing door trim panel and rear trim panel installation where they were required to impact a

simulation device with a vertical plate orientation at a rate of 5 impacts per minute. The height of

35

the vertical impact plate on the simulation device was 1.1 5m from the floor. A controlled height

was used in this study since Potvin & Chiang (1998) found no difierences between variable

positions relative to the body. Each impact position acquired by the subjects was screened so that

al1 subjects would adopt a similar impact position pnor to impact. An appropnate impact posture

included that of Figures 3.1 & 3.2 were subjects were limited to stand with both feet planted to the

floor to perform the required arm movements. The distances fiom the machine varied due to

different arm lengths, however al1 subjects were required to adopt similar positions relative to the

impact plate.

The signal to begin impacts was sounded by a metronome every minute. Subjects were

instructed to impact the machine as hard as they could without straining themselves or becoming

tired. weakened. overheated, or out of breath. The subjects were required to adjust the workload to

a resistance that they felt to be acceptable by tuming a nob on the pneumatic cylinder. Resistance

\vas increased or decreased after f 5 minutes by a random amount detennined by the researcher.

Again. the subjects were required to reset the resistance to acceptable levels. Data was collected

continuousiy during the last 120 minutes of the expenmental condition. Collection was

continuous for a11 5 conditions (palmerhare hand, palmedglove, and ulnar sidehare hand. ulnar

side/glove)(Figui-e 3.3). Between each condition, subjects were required to change impact

location or impact glove use. Time between the change in impact location required a minute or

less to remove or put on the impact glove before collection could resume. From this collection

force and acceleration time-histories fiom the last 30 minutes in each condition were coilected.

The first two impacts immediately after the experimenter reset the resistance were discarded

because they were not found to represent the subject's "acceptable" forces. The resistance was

36

changed by a random arnount by the experimenter and was not apparent to the subject. The

subject requires a number of impacts (approximately 2 impacts) to find their acceptable resistance

again. Since these impacts do not represent their tnie acceptable force they must be discarded.

Male

Gender

Female

Palm U lnar Posture

I G love

Bare Protection Hand

Figure 3.3: Al1 independent variables looked at in the current study.

3.4 DATA COLLECTION

AH data was collected using an impact simulation device (Figure 3.4) which was designed

to simulate the time-history of the hand impact forces required to insert pushpins during door trim

panel installation. The hand impact surface consisted of a I O x lOcm metal plate with its motion

resisted by a pneumatic cylinder. Subjects could adjust the resistance of the impacts to seat the

door trim panel by adjusting the knob on the pneumatic cylinder. A force transducer (Transducer

Techniques MLP-500-CO) was placed in series with the plate and pneumatic cylinder measunng

the force time-history (Figure 3.5) of each impact. On each subject, impact acceleration data

(Figure 3.6) were collected with a tri-axial accelerometer. The accelerometer was mounted to the

back of the impacting hand via a modified wristhand brace, which the participants wore dunng

the sessions.

All data were coilected and processed with LabVIE W software (version 4.1, National

Instruments) using a Macintosh Quatra 800 (68040/33,24MB RAM) with a 16 bit multifunction

[/O board (hrB-MIO- 1 GXL, National Instnunents). Al1 data were sampled at 2000 Hz. The

collection of each impact was triggered in the LabVIEW software by the sudden increase in force.

Trials were collected from 50 ms before the trigger to 150 ms after. Force tirne-histories and

acceieration time-histories were colfected for each impact of the collection session.

Impact Plate

Magnetic witches P l- ce Transducer

FoamNinyl 1 - ~ e a r i n ~ Track Base Plate \

Bearing Block - \ Bearing Slider

Figure 3.4: A schematic illustration of the door trim panel installation simulation device and the pressure adjustment dial to control resistance.

39

Figure 3 -5 : Sample accelerat ion-time history wi th measured variables indicated.

Figure 3.6: Sample force-time history with measured variables indicated.

3.5 DATA ANALYSE

Data from the last 120 minutes of the 180-minute collection session were anaiyzed (30

min. in each impact condition and impact location). The two impacts following any pressure

adjustment were removed fiom analysis because they were not felt to represent a normal trial

(Pot\-in Br Cliiang, 1998). Both the force and acceleration data were digitally filtered using a 4b

order. dual pass Buttenvorth filter with a 1ow cut off ffequency of 500 Hz to rernove aliasing.

When making contact with the simulation device the force-tirne history records generally only had

one peak. Impact force records with two peaks resembled impact with the surface followed by a

second peak were the surface bottomed out. The dependent variables were: a) peak force (N), time

to peak (ms), rate of loading (Nlms), and force impulse (N-s) and b) peak accelerations (dsls),

time to peak (ms), rate of acceleration (m/s/s/ms) and acceleration impulse (mk). The variables

used in tliis study were similar to those commonly used to quanti@ the severity of foot impact

diiring running and walking, and crash testing (Bishop, 1976; Henning et al. 1993; Lafortune,

199 1 ; Xigs et al.. 1987). The rate of loading was calculated to be the linear regression siope of

the force cume between 20% and 70% of the peak force and acceleration. Impulse was caIcuiated

to be the integral of the force-time and acceleration-time Cumes. Time histories were windowed

so tliat trial start and end points could be denved. A force threshold (5 N) was set so that the start

of each trial was defined as the fiame at which the signal exceeded this level, while the end point

\vas conversely defined as the fkame at which the signal retumed to a level below the threshold.

In addition. the resistance setting was recorded for each impact. ïh is value (in PSI) was

converted to a static force level given the cross-sectional area of the pneumatic plunger (0.44 in').

The static force (Ibs) was calculated as the PSI x 0.44 in' and then converted into Newton's.

41

Force and acceleration curves were windowed independentIy. The length of the window

for both cunres was chosen to be 50 ms. This window was deterrnined fiom previous research by

Potvin & Chiang (1998) which revealed impact duration to be between 35 and 60 ms. The start of

the window for the force data was found by using a threshold. Potvin & Chiang (1998) were

unable to find the start of the impact on the acceleration curve using a threshold method because

of variability in pre-impact acceleration both between and within subjects. Instead the start of the

acceleration window was found by digitally filtering the data using a 40th order, dual pass

Buttenvorth filter with a iow cut off fiequency of 300 Hz. This created an under damped

reproduction of the acceleration data. The derivative of this under damped curve was searched for

a local minimum (derivative = O). The location of this local minimum was used as the start of the

ac celerat ion window . Al1 further processing was completed on the original acceleration data

filtered u-ith the 4th order Buttenvorth filter at 500 Hz.

3.6 STATISTICAL ANALYSIS

A rnixed repeated measures 3 factor ANOVA was used to determine the effects of gender

(be t ween factor), impact protection (repeated measure), and impact location (repeated measure)

for the average values for each of the four conditions within the 30 min. of coflection and al1

dependent variables. Significance was tested at p c -05, and either < -01 or 2 < .001. Al1 mean

di fferences were analyzed using the SuperANOVA (version 1.1 1) software. Normal Tukey Post-

hoc contrasts were performed on dependent variables showing significant interactions (between

subjects) between impact protection and impact posture. Modified Tukey Post-hoc contrasts for

wirhinibetween interactions were performed on al1 dependent variables showing significance

42

behveen gender and either impact protection or impact posture. Seventy-fiAh percentile values

were calculated as the TLV for dependent variables on the basis of previous guidelines set by both

Snook (1 978) and NIOSH (198 1). These values have been determined by subtracting 0.675

standard deviations (mean - (stdev. x 0.67)) fiom the means of peak, rate, and impulse variables

(where lower values were less severe). Means and standard deviations were calculated for each

factor. Coefficients of variation (CV: standard deviation as a percentage of the mean) were

calculated for al1 dependent variables to determine the consistency, within subjects, for the final

30 minutes of each session (30 x 4=120 minutes total). Finally, correlation coefficients were

cal cul ated Lvi t h the means of each variable, for each posture (palmerhlnar) and impact protection

(glo\-eho glove) for force, and acceleration, variables to resistance setting.

Chapter 4: RESULTS

The results of this snidy have been subdivided into six sections within this chapter. The

first section deals with the variability data for al1 impact conditions (bare/palm, bare ulnar, glove

palm. glove ulnar). The second section looks at al1 the force variables (PK Force, TTPK Force,

LR Force. and Force Impulse) and al1 impact conditions. The third section illustrates the effects

on the acceleration variables (PK Accel., TTPK Accel., LR Accel., and Accel- Impulse) and al1

impact conditions. The fourth section presents the results of al1 subject effective masses. The

fifth sections shows the calculated recommended tolerance limits for gender with the final section

looking at al1 dependent variables measured and subject correlation to resistance settings cbosen.

WitIiin the various conditions (gender, protection, & posture) significance of al1 dependent

variables esamined was shown to be significant either at E < .001, P < .O1 or, 2 < .05. Mean and

subject \*a-iability data were taken fkom the various impacts perfomed for each thirty-minute

condition (bare palm, bare ulnar, giove palm, and glove ulnar) during the final N o hours of

collection. Al1 significant main effects will be presented in graphs with percent differences

indicated in the text. Al1 rnean values and standard deviations will be presented in Table 1C in

Appendix C. Figures 4.la & b, and 4.2a & b reveal some of the sample time histories for the PK

Force. Force Impulse, PK Accel., and Accel. Impulse variables respectively, for one subject.

Eacli time history represents the range of impacts performed during a final 2-hr collection session.

The low variability found for Figures 4.1 a &b and 4.2a & b signifies well-trained subjects. This

tightness signifies that the variable is controlled by the subject to determine safety impact limits.

Figures 4.1 a & b: S-ple time-histones for peak force and force impulse over the course of one 2-hour data collection session for one male subject.

Figure 4.2a & b: Sample time-histones for peak acceleration and acceleration impulse over the course of the final 2-hour data collection session for one male subject.

4.1 V.4RIABILITY DATA

It was assurned that the variables showing the greatest consistency within subjects may

have been the variables that were being controlled by the subjects in this psychophysical study.

The cutoff reliable variability was set at 20%. Since this value variability was rneasured to be

double the lowest variabiIity value found, and appeared extreme to the other variability values

collected. Values above 20% variability were not deemed reliable enough to draw conclusions.

As seen in Table 4.1, Impulse was the most repeatable variable for acceleration and force with

average coefficients of 9.6 % and 1 1.7% respectively. Peak acceleration also showed to be very

repeatable with a coefficient of variation of 11%. Load rate for both force and acceleration was

highly variable. with variability's of 24.8% and 21.4% respectively and were not used to draw

any conclusions.

Table 4.1 : Within subject coefficients of variation (CV) for each variable, expressed in percent values (%). Values have been pooled across a11 conditions, within each gender, posture, & protection (n= 16).

Load Rate l 21-4 1 18.3 Accel

Dependent AN Males Va ri ab les 1 Dain /

[der Posture Protection Females Pa lnz Uhar Bore Glo ve

.13.8 14.7

23.2

10.7 9.0

17.4

PK Force TTPK Force Load Rate Force IMPF PK Accel

14.8 14.4

24.8

11.7 11.0

TTPK Accel

4.2

the

FORCE VARIABLES

Through the various impacts with the simulation device, there was usualIy a first peak in

force record associated with the initial contact with the device, and then a second peak

associated with the simulation of the door trim panel coming into contact with îhe door. The first

peaks were almost always higher then the second. The maximum values found within the fint or

second peaks were recorded. The dependent variables measured included Pk Force, TTPK Force,

LR Force and Force impulse.

1 ) Peak Force (PKF)

Significance for peak force was found for the gender, F (1,14) = 5.67 (15 c .OS) and

protection. E ( 1.14) = 5.9 1 (1! c .05) conditions. Posture failed to demonstrate a significant main

e ffec t. F ( 1 .14) = 1 -54. Figure 4.3 il lustrates the mean gender effects pooled across both posture

and protection for peak force. The pooled average for male peak force was found to be

signi ficantly larger (by 65%) than their femaIe counter parts within both the posture (palm vs

uli~ar) and protection conditions (bare hand vs glove).

Figure 4.4 shows the mean protection effect for the use of impact gloves. The use of

impact gloves was found to result in higher impact peaks (PK Force) than that with the bare hand

(by 7%).

Female Male

Gender

Figure 4.3: A cornparison of the mean values for gender (male vs female) for peak forces eserted by al1 subjects during the study. Data has been pooled across al1 conditions for peak force (Each gender bar n=8). Al1 error bars represent the standard error.

Bare Hand Glove

Protection - -

Figure 4.4: The effects of hand protection and the development of peak force during the final 2-hour collection session. Glove being greater than the bare hand. (Each protection bar n =16). Al1 error bars represent the standard emor.

2) Force Impulse

Force impulse showed an interaction effect between gender and protection, F (1 ,l4) =

13.29 (2 < .O i ) (Figure 4.5). Comparing females to males across protection revealed that males

produced higher force impulses than females (by 60%). Also. force impulse was higher for the

elove condition than that for the bare hand condition (by 16%). The glove use was found to C

significantly increase force impulse values by 9% for females @ < .05j, and 20% males (e < -01).

Significance was also found for posture, (1 ,l4) = 5.35 (e < -05). The average palmer values

ix.ere observed to be 10% higher than the uhar values for force impulse (Figure 4.6).

Fernale Male

Gender

- Bare - - - - - Glove .- -

-. - -

Figure 4.5:Shows the interaction between protection and gender for Force Impulse (Each gender value for bare & glove n=8). Al1 error bars represent the standard error.

Palm Ulnar

Posture -

Figure 4.6: The Force Impulse means for posture for al1 subjects dunng the final 2-hour collection session (Each posture bar n=16). Al1 error bars represent the standard error.

3) TTPK Force

For TTPK Force, gender and posture faiIed to show any significant effects, F (1,M) = 4.84

and E ( 1.14) = 2.02, respectively. However a significant difference was found for protection,

( 1.13) = 1 3 -88 (e < .O 1 ). Figure 4.7 illustrates the effects of protection for TTPK Force. As

sliosrn in Figure 4.9, the use of gloves resulted in higher TTPK Forces (by 11%) than the values

for the bare hand.

4) LR Force

Force load rate variables were found to be highly variable and therefore least reliable and

wilI not be used to draw Our conchsions.

Bare Glove

Protection - - -

Figure 4.7: The mean TTPK Forces for the protection condition of the final 2-hour collection session (Each protection bar n=16). AI1 error bars represent the standard error.

4.3 ACCELERATION VARIABLES

I ) Peak Acceleration

Of al1 independent variables measured, only protection @< -05) and posture (e< -05)

sliowed significance, ( 1 ,l4) = 5.82, and F (1,14) = 4.78, respectively. Gender values were

found to be non-significant, (1,14) = 1.1 1. Figure 4.8 illustrates the effects of protection on PK

Acceleration. It can be seen that bare hand accelerations were higher @y 4%) than glove impact

accelerations. The results reveal that the palmer condition produced higher peak acceleration

values (by 9%) than the uln. condition (Figure 4.9).

Bare Glove

Protection

Figure 4.8: The mean Peak Acceleration values for the protection condition for the final 2 hoiir collection session (Each protection bar n=16). All error bars represent the standard error.

Palm Ulnar

Posture . -

Figure 3.9: The mean Peak Acceleration values for the posture condition for the final 2- hour collection session (Each posture bar n=16). Al1 error bars represent the standard error.

2) Acceleration Impulse

Gender and protection failed to show any significance, F (1,14) = 1 -82, and F (1,14) =

0.36, respectively. Posture however, revealed a strong significant main effect for acceleration

impulse. F ( 1.1 4) = 1 7.5 8 @ c .001). The uhar condition was found to have a higher acceleration

impulse (by 1 9%) than that found for the palmer condition (Figure 4.10).

Palm Ulnar

Posture

Figure 4.1 O: A cornparison of the mean values of Acceleration Impulse for posture (Each posture bar n=16). Al1 error bars represent the standard error.

3) TTPK Acceleration

TTPK Acceleration resulted in a significant interaction effect between posture and gender.

Significance was found to be at, F (1,14) = 4.68 @ c -05). Figure 4.1 1 illustrates these effects.

The average ulnar TTPK acceleration was 26% higher than the palm (e c -01) and this difference

was found to be 45% in the male subjects @ c -05) and insignificant for the fernale subjects.

Figure 4.1 1 : A cornparison o f the mean TTPK Acceleration values for the posture & gender interaction (Each gender value for palmer & ulnar n=8). Al1 error bars represent the C-

standard error.

4) Rate of Acceleration

Rate of acceleration variables were found to be highly variable and therefore were

considered to be the least reliable and wilI not be used to draw our conclusions.

4.4 SUBJECT EFFECTIVE MASS

Data collection included the measurement of force and acceleration. Given the

relationship: Mass = ForceIAcceleration it was possible to mesure the "effective mass" of the

impacting am1 for each of the sixteen subjects. The calculated effective

shoum in Table 1E in Appendix E. The effective m a s of the impacting

mass for each subject is

a m for males was found

to be 37% greater than females and the use of impact glove

12%. Posture was found to affect the anns effective mas.

greater impact ami effective mass than the palrn.

increased the a m effective mass by

The ulnar posture resulted in a 1 7%

4.5 RECObI3IENDED IMPACT LIMITS

The recommended Threshold Limits for male, and females are shown in Table 4.2. The

recornn-iended limits for peak force and forces impulse were found to be: 228.7 N, and 3.13 Ns for

males. 124.3 N. and 2.05 Ns for females.

Table 1.2: Recommended threshold limit values for each variable based on 75" percentile values at 5 impactdminute. Female values should generally be used unless males are performing the task exclusiveIy.

-

Male Limits PK Force TTPK Force Force l mpulse P K Accel . TTPK Accel.

Glove Glove Palm

245.5 4.54 3.74

433.9

Bare Hand Glove Ulnar

238.5 4.92 3.23

366.8

Bare Palm

228.7 4.1 5 3.1 3

463.0 4.04 3.981 5.88

Bare Ulnar

208.0 4.72 2.66

391 .l 5.59

Female IUmits

4.6 CORRELATION DATA

Al1 dependent variables

Bare Hand Bare Palm (Bare Ulnar

measured were correlated with the resistance settings chosen

Glove

the subjects during the final data collection period. Previous work by Potvin & Chiang (1998)

found force impulse to show the highest correlation with resistance setting ( ~ 0 . 8 2 ) . The findings

Glove Palm

of the current study however, reveal that it was PK

A11 correIation other correlation data c m be found

Glove Ulnar 1

force ( ~ 0 . 7 2 ) and then force

in Table ID, in Appendix D.

impulse

Chapter 5: DISCUSSION

The discussion is divided into five sections. The first section provides a brief description

of our major findings (Surnrnary). The second section deals with the results and our hypotheses

for the experiment (Hypotheses). The third section will address the limitations of the

esperiinental protocol (Limitations). The fourth section will discuss variability data and other

interesting frndings found in the study (Other Interesting Findings). The final section will discuss

what tliese current findings mean to industry (Implications to hdustry).

5.1 SUhlhIARY

The current study used a psychophysicaI methodology to establish acceptable impact

severity levels during door trim panel installation for different hand postures (palmer vs ulnar) and

protection conditions (bare vs glove). Measured variables in the current study included peak,

impulse. TTPK, and load rate for both force and acceleration. The force variables measured the

estemal force the subjects found acceptable and the acceleration variables provided information

on the resulting severity to the hand. Previous studies have used similar variables as the current

study to summarize components of force and acceleration time histories considered to be directly

related to the developrnent of CTD's.

It was assumed that the variables showing the greatest consistency within subjects were

the variables that were likeiy being controlled by the subjects and the variables most reliable from

wliich to draw Our conclusions. Force, force impulse, peak acceleration, and acceleration impulse

kvere found to be the most reliable measures. Since the within subject variability for force and

acceieration load rate were not satisfactory enough to deem reliable, these variables will not be

used to draw conclusions.

The current study f o n d males to accept impacts with significantly higher peak forces (by

65%) and force impulses (by 59%) than their female counterparts. With this increase in

acceptable force by males. no statistically significant differences were found in the acceleration

data. However. males did demonstrate a non-significant trend to have higher peak accelerations

(by 1 7%) and acceleration impulses (by 2 1 %).

Impact $ove use was also found to result in significantly higher peak forces (by 7%),

force impulse (by 16%) and TTPK forces (by 11%) than the bare hand conditions. Peak glove

acceleratioi~s indicate that, although the gloves did indeed allow for higher impact forces, gloves

were also successful in slightly lowering peak acceleration by 4%. Thus, glove use was found to

increase acceptable forces without increasing impact severity to the hand. However, the benefits

of =love use appeared to be more pronounced for the male subjects.

Evidence to suggest the palm allowed for higher acceptable impact forces was the finding

that the palm was found to tolerate 10% greater force impulses. However, the effect on

acceleration was unclear. The palm accepted higher peak accelerations @y 9%) and much lower

TTPk acceleration (by 2 1 %). Interestingly, the ulnar acceleration impulse was fourid to be

greater by 19%. Our findings show subjects accepted larger force impulses and severities for the C

palm, however, it was difficult to Say what these acceleration findings mean to the hand. It u7as

concluded that these findings warrant further investigation.

5.2 HYPOTHESES

Gender Effects: It was hypothesized that males would accept higher impact forces than

fernales. Findings fiom Potvin & Chiang (1998), aithough non-significant, found a trend for

males to tolerate greater impact forces, force impulses, and smailer T ï P K forces. Impact forces

are mainly determined by velocity of the ann at impact, the effective mass of the arm, îhe area of

contact, and the material properties of the damping elements (soft tissue, materials, etc.) (Nigg,

1987). Several in vitro studies looking at lumbar spine compression force tolerance limits have

sho\\.n males to tolerate larger compression forces than females (Jager & Luttman, 199 1 ; NIOSH,

199 1 : Mital et al. 1993). Previous psychophysical studies by Snook (1970), Ayoub (1978), and

Snook and Ciriello (1 991) have determined maximal weights and forces for various lifiing,

lo\vering. pushing, pulling and carrying tasks also showing that males are able to tolerate greater

amounts of forces than females. A study by Hall (1997) have also shown males to have Iarger

pressure pain tliresholds then females suggesting that individual pain tolerances can also have

large effects on the forces subjects find acceptable.

The inale subjects in the current study were observed to have greater body mass (by 52%)

and effective mass of the contacting arm (by 37%) than the female subjects. The experirnental

results support Our hypotheses and illustrate that males were able to tolerate much greater peak

impact forces (by 65%) and force impulse (by 59%) than females. There was also an insign

trend towards the TTPK force being 11% higher for females. Although males were found to

experience larger impact forces and force impulses compared to females, no significant

di fferences were observed for the acceleration variables. However, males were observed to show

an insignificant trend to accept higher peak accelerations (by 17%) and acceleration impulses (by

60

- 3 1 %). The larger a m effective mass values found for the males the study may account for the

similar acceIeration values found. Male subjects were found to accept significantly higher forces

but the difference in acceleration and acceleration impulse was less pronounced (non-significant)

civen the di fferences in effëctive mass of their respective impacting arms. Thus, maies were - found to produce Iarger forces than females with similar impact severity.

Protection Effects: It was hypothesized that @ove use would decrease impact severity (lower

acceleration) as well as increase the level of impact tolerated (higher force production) by the

subjects. As discussed in section 2.3, previous research in running and shoe design has illustrated

high impact force peaks to be strongly correlated with the occurrence of pain and injuries

(Lafortune & Lake, 1995; Nigg, 1987; Nigg, 1988). These studies have not only looked at impact

forces themselves but have looked towards ways in order to lower these injurious force peaks and

shockwaves associated with impact. It is assurned that there is a connection between cushioning

and impact force. It is speculated that impact forces can be influenced (lowered) through the

insertion of material properties (eg. Sorbothane) before impact (IEM Medical Technologies Inc.,

1998; Sorbotliane Online, 1998). Sorbothane claims to be more efficient than other matenals

because i t is visco-elastic, allowing it to disperse shockwaves and lower the forces t~ansmitted

through the body (IEM Technologies Inc., 1998). Hammer impact testing by Noe et al. (1993) to

test the shock attenuation ability, found sorbothane to attenuate 93% of the peak accelerations.

Other studies looking at running have also found visco-elastic insoles to affect impact forces and

reduce acceleration amplitudes (Light et al., 1979; MacLellan et al., 198 1 ; Voloshin, 1986;

Volusliin 8: Wosk, 198 1 ).

Our current findings support our hypotheses. The findings show that impact gIove use

resulted in an increase in acceptable peak impact force, force impulse, and TTPK forces

respectively (by 7, 16, and 11%). It was apparent by looking at the acceleration data that the use

of impact gloves was also successful in slightly lowering the severity (by 4%) of the impacts

despite the increases in peak force found in the study. This decrease in severity may appear

mi nima1 but if looked at over a period of several thousand impacts its worth is far greater. The

findings also reveal that the male population benefits most from glove use. It is possible that

fernales n-iay be more conservative in their impacts with the glove. It seems that due to the unique

properties of sorbothane, and its visco-elastic nature (rate dependent), subjects were able to

tolerate greater impact forces as well as lower severity to the hand. Although, our findings show

niales beiiefit more from its implementation.

Iinnact Posture Effects: It was hypothesized that impact location @alm vs ulnar) would have

an effect on ones tolerance to impact force. Robbins et al. (1989) have stated that the planter &

palmer surfaces show similarities to each other. With this in mind the palrn may aIso share the

ability to absorb impact forces. Potvin & Chiang (1998) found that subjects chose to impact the

delaice using the palmer surface. It was further hypothesized that the subjects chose this posture

because i t was better suited to the task and would then result in the production of higher impact

peaks and tolerances. The peak force data collected in the study revealed no significant

differences between the palmer and ulnar impact surfaces. However, the palm was associated

with higher force impulses (by 10%)- than the ulnar posture supporting our hypothesis that the

palm would have a greater tolerance to impact. The palm was also associated with higher peak

62

accelerations. Interestingly, the acceleration data found the ulnar posture to have larger

acceleration impdses (by 19%) and TTPK accelerations @y 26%). There is evidence to suggest

tliat the palrn was able to tolerate larger forces, however the differences in seventy were

i nconc lusive and wi Il be discussed latter in section 5.4 (Interesting Findings).

5.3 LIbIITATIONS

The limitations of the psychophysical methodology and the assumptions made in this study

must be recognized before conclusions c m be accepted. The primary advantage to the

psychophysical approach is that it pennits the realistic simulation of industrial work (Snook,

1985). For the purpose of the study a simulation device was used to simulate door trim panel

installation (Figure 3.13). The impact device was designed to measure the time-history of the

iiand impacts required to insen push-pins dunng door trim panel installation. The simulation

impact surface matenal was constructed of foamhinyl over a metal plate and did not necessady

resernble the door surface were slight differences in trim interfaces can Vary with installation. The

siri~ulation involved similar impact frequency, but allowed subjects to adjust the resistance of pin

insertion to values found to be acceptable. It is important to note that the simulation device only

closeIr resembled door trirn installation, and was not the real industrial task.

I t is also important to note that the findings in this study pertaining to impact gloves can only

be drawn about the specific gloves used within the current study. The results were specific to the

gloves tested and cannot be drawn to resemble the effects found for other impact glove types.

Using a psychophysical methodology errors can occur, therefore subjects require training

with the simulation device and the methodology to do this reliably. Within the current study,

63

subjects were trained on the simulation device and the separate conditions before an evaluation

ueas made on their acceptable limits. In total subjects had 7-hrs of contact time with the

simulation device. Al1 subjects had 5-hrs training and 2-hrs of collection. The training of each

subject consisted of two 2-hr collection sessions, and a final 3-hr session, which involved an

additional 1 -hr training and the final 2-hr collection. Thus, each subject received 1 -hr 15 min of

simulation training in each of the four conditions before a h a 1 collection was performed.

Since subjects did not do al1 the training and testing in the same day it was important to have

the training and collection sessions in close proximity in order to lower the chances of losing any

training effects. ïh is was followed for each subject, but not al1 subjects experienced the sarne

tinle frames during training. Subjects that were off for longer periods of time were re-trained

before a coIlection session was made. Our cument findings show that the within subject

variability \vas very low and within an acceptable range for reliabiiity. Our values were similar

to those findings of Potvin & Chiang (1998). The variability between subjects however was

slion-n to be hieher. This finding may have been the result of different subject anthropometrics,

subject hand damping properties, or pain tolerances of the subjects used in the study.

In order to produce a lab task that simulated the industrial task of interest (trim installation)

several control variables wère ignored. For example, such things as ami swing distance, arm

angle, feet distance fiom the simulation device, or the relative height of the simulation device

were not controlkd. By doing this, the lab simulation would better resemble the actual industrial

task. By not providing a large number of controls for the subjects it was believed that each

subject would provide a better representation of their impact severity limit for the industrial task

of trim installation. Giving subjects the fieedom to impact the device in manner that was most

64

corn fortable to them and providing a bue representation of the industrial task, it was believed that

more accurate impact severity limits would be produced.

.41so. although only 8 male and 8 fernale subjects participated in the current study our

findin~s appear to be very reliable. Our findings for bare palm, were similar to those findings of

Potvin & Chiang (1998), who studied bare palm impacts for 27 subjects. The intent of this study

\vas to determine the relative differences found between conditions rather than the absolute values

obtained. With this in mind, the strength of the current study was also supported by the findings

of significance as low as p < -01.

5.4 INTERESTING FINDINGS

1 ) Posture

I t was our hypothesis that impact posture would affect impact tolerance with the palm

toleraring liiglier impact forces. However, impact posture did indeed affect impact tolerance. The

palm \\.as fotind to accept significantiy greater force impuises than the ulnar surface. These

findings reveal subjects were able to tolerate hitting the device with greater momentum in the

palmer posture. Robins et al. (1989) have stated the palm shares similarities with the plantar

surface (heel fat pad). Both surfaces consist of similar outer layers of glabrous epithelium

covenng a specialized adipose tissue, that consist of a dense network of fibrous trabeculae which

linlit horizontal movement, and have a high density of mechanoreceptors, nociceptors, and

meissner carpuscles. These similarities suggest that the palm of the hand may respond sirniiarly

to the heel fat pad during ruming, acting to lower impact peaks (Ben.net & Ker, 1990; Ker et al.,

1995) and protect the heel bone by expanding in the transversal plane to limit excessive local

65

stresses (Declercq et al., 1994). This may also account for the tolerance of higher force impulses

obsenred for the palm.

The palm was also found to tolerate 9% higher peak accelerations than the ulnar posture. The

lower accelerations in the uinar posture may be a result of the 17% greater ulnar a m effective

mass. The higher palmer peak accelerations, smaller TTPK accelerations, and acceleration

impulses rnay not necessarily be negative simply because they were tolerated by the subjects. The

possibility that the palm ma-y in fact act like the heel fat pad may explain our findings. The palm

like the heel fat pad once depressed c m fiirther resists horizontal moment creating a larger solid

surface during impact. Creating a larger surface area to accept the impact may have resulted in the

tolerance of the larger force impulse observed by the palm.

The ulnar posture was found to experience, smaller force impulse, peak acceleration, larger

TTPK acceleration, and larger acceleration impulses. The production of larger acceleration

impulses u i t h smaller peak acceleration was not clear at the moment. The palmer surface appears

to be more tolerable to force, but the acceieration findings remain unclear. Not enough

information \vas avaiIable, making the determination of impact severity dificult. Our findings

\varranting further investigation before an accurate conclusion about impact posture and seventy

can be made.

2 ) Controlled Variables

Other interesting findings in the current study involved the measurement of a number of

variables to characterize the severity of each impact. Tt was assurned that the variables that were

being controlled by the subjects would show the greatest consistency within subjects. Potvin 8r

66

Chiang ( 1998). found impulse to be the most repeatable variable for force in studies 1 & 2 and

acceleration in study 2, with average coefficient variations of 996, 12%, and 14% respectively.

The findings of the current study also reveal impulse to be the most repeatable variable among

each subject. However, it was the acceleration impulse having the lowest variability (10%). This

value was followed by, peak acceleration, force impulse and peak force, with average coefficients

of 1 1 %. 12%. and 15% respectively. In addition, Potvin and Chiang (1998) found force impulse

to show the highest correlation with the resistance setting being controlled by the subjects on the

simulation device. Our findings suggest that it was peak force (r=0.72) and then force impulse

(r=O.GS). Our findings differ from those found by Potvin and Chiang (1998). These differences

may be the result the experiment itself, which incorporated different postures during impact and

altered perceptive states with and without the use of impact gloves. This organization of

conditions perhaps required a different means to establish reliable impact tolerance limits. For

our esperinient i t appears that subjects monitored their accelerations more closely. Due to the

clianginp perceptive states subjects elected to monitor acceleration impulse rather than their force

impulse to produce reliable tolerance limits. The goals of the expenment were the same as that of

Pot\.in & Cliiang ( 1 998), although subjects chose a different means to give their tolerance limits.

3 ) Recornmended Acce~tabie Im~ac t Lirnits

Snook (1978) established a Threshold Limit Value (TLV) at the 75"' percentile for both

males and females based on insurance data indicating that the risk of low back injury was three

rinies higlier if a lifting task was acceptable to less than 75% of the working population. The TLV

values were calculated for each of the variables measured in the study (Table 4). Differences

67

between male and female subjects warrant separate 75' percentile values, special attention should

also be placed on recommending limits were both male and females perform the same jobs. The

recommended Threshold Limits for male, and females are shown in Table 4.5. The recommended

limits for peak force and forces impulse were found to be: 228.7 N, and 3.13 Ns for males, and

121.3 N, and 2.05 Ns for females.

5.5 iRIPLICATIONS FOR INDUSTRY

The results of the present study for gender, protection, and posture can provided important

inforniation to industry. Research by Potvin, Fraser, & Murphy (1999, Subrnitted) dnne to

evaluate hand impact severities associated with various trim installation tasks show peak forces of

up to 788 N. It was also found that 21 of 28 jobs looked at were found to be acceptable to less

than 25% of the working population, compared to an estimated fiequency dependent tolerance of

273 K. Tliese values suggest that a problern does exist, and perhaps the current study rnay

pro~.ide some needed answers.

The findings of the current study show males of accept larger external peak forces to

objects than femaies with sirnilar seventy values. Recomrnended threshold limit values have been

caiculated for Male, Female, and both genders for each of the impact conditions (Table 4). The

recommended peak force limits for male bare hand, protection and palmer and ulnar postures were

found to be 228. 7 N, 245.5 N, 208.0 N, and 238.5 N respectively. The recomrnended peak force

lin-iits for female bare hand and protection palm and ulnar postures were found to be 124.3 N,

1 27.7 ru'. 1 5 3.2 N, and 1 58.5 N respectively. Female peak force tolerance limits differ greatly

frorn the male values observed in the study with similar severities to the hand. This large

68

discrepancy benveen male &d fernales warrants that special care needs to taken to recognizize these

gender differences especially if both genders are perfoming the sarne job. Due to female's lower

tolerance io peak force than males, females appear more at risk at developing problems on the job.

The implementation of protective gloves has allowed subjects within the current study to

accept liiçher peak forces as well as lower the overall severity to the hand. The use of these

protectiire gloves within industry will allow subjects to tolerate greater impact forces on the job

without causing an increase in severity. Thus, workers are better able to protect thernselves.

Hov.e\,er males appear to benefit more fiom its use than females. This poses a problern because

olove use does not appear to help female tolerance limit values. Differences between bare/glove - for female and male subjects were 9 and 20% respectively. This finding again warrants that

special attention should be placed on those jobs in which both males and females are perfoming.

It appears that glove use for females may not be the answer to increase tolerance and perhaps

special tools such as mallets should be considered.

IVitliin industry the hand is used to impact parts were impacts are performed using

difierent haiid impact locations. This study looked at palmer and unlar impact locations on the

hand. The paIm is usually associated with door trim installation where the ulnar posture is mostly

used for 01-erhead rear tailgate installations. The current study however did not look at overhead

impacts, but focused primarily on impact location. The findings of the current show that the palm

of the 11and can accept larger force impulses and peak accelerations than the ulnar posture. It

appears that the palm was more suited to withstand impact forces, since the ulnar posture was

found to accept lower force impulses, and peak accelerations. The actual severity to the hand with

these postures however was not clear. The palm did accept higher peak accelerations and much

69

lower TTPK's. However, the ulnar posture was found to have higher acceleration impulses and

TTPK acceleration. The findings of the curent study suggest that the palmer posture was better

suited to tolerate impact forces. Severity on the other was inconclusive and requires further

investigation.

Chapter 6: SUMMARY AND CONCLUSIONS

This chapter provides a surnrnary of the previous five chapten. The following sections

surnmarize the methodology and results chapters, and make suggestions for further study from the

current findings.

The purpose of this study was to expand on the findings of Potvin & Chiang (1998) using

a psychophysical rnethodology to establish acceptable impact seventy limits for impacts of a

vertical surface using a simulated door trim panel installation task with different hand impact

postures witli and without the use of impact gloves.

6.1 SU3.13IARY OF METHODOLOGY

The independent variables examined were gender, hand posture (palmer vs ulnar), and

protection (bare hand vs impact glove). A 3 factor ANOVA was used to determine the effects of

gender (between factor), impact protection (repeated), and impact location (repeated) for the - a\-rrage \dues for each of the four conditions within the 30 min. of collection and al1 independent

variables.

Subjects participating in the study were 16 paid volunteers, 8 male and 8 females drawn

from a uni versi ry population. Each subject participating had not suffered any upper extremity

injury or pain in the last 6 months prior to testing.

A specially constructed door trim installation simulation device (Figure 3.13) was

coiistructed to sirnulate the time-history of the hand impact forces required to insert push pins

during door tnm panel installation. Each had an impact surface (1 0 x 10 cm) with its motion

resisted by a pneumatic cylinder. Using an adjusting knob subjects were allowed to manually

adjust the resistance of the impacts to seat the push-pins to levels they found comfortable. A force

transducer was placed in series with the plate and pneumatic cylinder measuring the force time-

history of each impact. On each subject, impact acceleration data was collected using a triaxial

acceleron~eter mounted on the back of the hand via a modified wrist/hand brace, which the

participants wore during the sessions.

For each dependent variable (peaks, impulse, T'T'PK's, & load rate) for force and

acceleration a 3 factor ANOVA's were used to determine the existence of significance's between

gender, impact protection, and impact posture, as well as any significant interactions (Q < -05).

Subsequent post hoc test were in the form of Tukey's Studentized Range (WSD) test (e( -05).

6.2 SU3131ARY OF RESULTS

The current study detemined that males were able to accept significantly greater external

forces and force impulses. A lack of significance found for the acceleration data reveal that male

and fernale severity levels are similar even though males were found to accept Iarger extemal

forces to the hand. Although non-significant, males did show a trend to accept larger peak

accelerations, and acceleration impulses. Males were aIso found to have higher limb effective

mass causing larger forces with similar accelerations, as observed in the current study.

The addition of protection through impact glove use resulted in subjects accepting greater

impact forces on the external object, longer TTPK forces, as well as slightly decreasing the

severity to the hand. Glove use allowed subjects to impact the object harder with about the same

or lourer acceleration of the hand decreasing severity. The male population was also found to

benefi t more from the impact glove use.

Impact posture revealed that the palm of the hand showed a greater tolerance to impact

force. The palm of the hand was found to accept larger force impulses, peak accelerations, and

TTPk accelerations than the ulnar posture. However the palm was found to have higher

acceleration impulses than the palm. The data suggests that the palm c m accept more severe

impacts to the hand, especially for the male population.

6.3 FUTURE DIRECTIONS

The current study was perfoxmed to expand on the hdings of Potvin & Chiang ( 1998). Using

a psychophysical methodology, our purpose was to establish acceptable impact severity limits for

impacts on a vertical surface using different hand impact postures with and without the use of impact

doves. Our findings were able to show that mdes were able to tolerate larger forces than females - \s.itliout any significant differences in impact severity. It was also found that the glove enabled the

subjects to tolerate larger impact forces with Iower severity values. Posture data showed that the

acceptable forces seemed to be higher for the palm but the effects on acceleration were inconclusive.

Further investization should be done to try and understand the shock absorbing capabilities

of the different impact surfaces on the hand (palm vs ulnar). It was not evident fiom our results to

conclude why the palm expenenced a larger tolerance or why the ulnar posture produce higher

acceleration impulses with Iower peak accelerations. Further work in this area should look to

det ermine the biomechanical response of these tissues to impact loading to reveal how much damping

may occur or how much surface contact at impact occurs to affect tolerance or shochwave absorption.

73

Emphasis should also include an extensive analysis of the separate impact postures to gather

information on the entire arm link system upon impact. This may include EMG activity occuring in

the hand and forearm musculature, accelerometer measurements at the hand, wrist and elbow, as well

as video analysis of the hand at impact. This information may prove more beneficial in detennining

a more effective impact posture that cm be utilized within the industrial setting.

Since the curent study only looked at the ulnar posture outside its industrial setting, it is

suggested that since the ulnar posture is fkequently used in overhead impacts it should be looked at

in a setting where most of the ulnar trim installation occur. Special attention should also be placed

on looking at EMG data to determine how fatigue of the muscles involved affected tolerance limits

and impact severity value

REFERENCES

Aerts. P., & De Clereq, D. (1993) . Deformation characteristics of the heel pad region of the shod foot during a simulated heel strike: the effect of varying midsole hardness. Joumal of Sports Science. 1 1, 449-46 1.

Aerts, P., Ker, R.F., De Clercq, D., Ilsley, D.W., & Alexander, R. (1 995) . The mechanical properties of the human heel pad: a paradox resolved. Journal of Biomechanics. 28 ( 1 1) , 1299-1308.

Anderson, M.K., & Hall, S.J. (1995) . S ~ o r t s Iniurv Mana-zement. Philadelphia, PA: Williams & Wilkens.

Armstrong, T.J. (1983) . An ergonomic guide to carpal tunnel syndrome. Arnerican Industrial Hvoiene Association Joumal.

;\rmstrong. T.J., Castelli, W.A., Evans, F.G., & Diaz-Perez, R. (1984) . Some histological changes in carpal tunnel contents and their biomechanical implications. Joumal of Occu~ational Medicine, 26. 197-20 1.

Armstrong, T.J., Radwin, R.G., Hansen, D.J., & Kennedy, K.W. (1986) . Repetitive trauma disorders: job evaluation and design. Human Factors. 28, 325-336.

Arn~strong. T.J., Fine, L.J., Goldstein, S.A., Lifshitz, Y.R. & Silventein, B.A. (1987) . Ergononiics considerations in hand and wrist tendinitis. Joumal of Hand Sureerv. (lZa), 2 pt 2, 830-837.

Armstrong, T.J., Punnett, L., & Ketner, P. (1 989) . Subjective worker assessrnent of hand tools used in automobile assembly. Arnerican industrial Hwiene Association Journal. 50 (12), 639-635.

Ayoub, M.M, Bethea, N.J., Deivanayagarn, S., Asfour, S.S., Bakken, G.M., Liles, D., Miral. A.. & Sherif, M. (1938) . Determination and modeline of liftine capacitv. HEW (NIOSH) Grant No. SR0 1 OH-000545-02, Lubbock, Texas.

Bennet. M.B., 8r Ker, R.F. (1990) . The mechanical properties of the human subcalcaneal fat pad in compression. Journal of Anatomv. 1 7 1, 13 1 - 138.

Berhang, A.M., Dehner, W., & Fogarty, C. (1974). Tennis elbow: a biomechanical approach. Joumal of Sport Biomechanics. 3,235-260.

Biship. P.J. (1976) . Dvnamic Remonse Critena For The Desien Of Ice Hockev Helrnets. University of Minnesota, Facsimile Reprint. Ann Arbor Michigan, University Microfilms International.

Cavenajh, P.R., Valiant, GA., & Misevich, K.W. (1984) . Biological aspects of modeling shoe/foot interaction during ruming. In E. C. Frederick (Eds.), S~ort Shoes and Plaving Surfaces pp. (24-46) . Charnpaign, Illonois: Human Kinetics Publishing.

Chaffin, D.B., & Anderson, G.B.J. ( 1 984) . Occu~ational Biomechanics, New York: Wiley.

Ciriello, V.M., & Snook, S.H. (1983) . A study of size, distance, height, and fiequency on rnanual handling tasks. Human Factors. 25,4730483.

Ciriello, V.M., Snook, S.H., Blick, A.C., & Wilkinson, P.L. (1990) . The effects oftask duration on psychophysically detemined maximum acceptable weights and forces. Ereonomics, 3 3 (2). 1 87-200. -

Clenlent, D.B., Taunton, J.E., Smart, G. W., & McNicol, K. (1 98 1 ) . A survey of overuse ruming injuries. Phvsician Sports Medicine. 9,47-58.

Christensen, H. (1 986) . Muscle activity and fatigue in the shoulder muscles of assembly- plant employees. Scandinavia Journal of Work Environmental Health. 12. 582-587.

Coury. H.J.C.G.. Kumar, S., Rodgher, S., & Narayan, Y. (1998) . Measurements of slioulder adduction strength in different postures. International Journal of Industrial Er~onomics, 22. 195-206. -

Dahalan. J.B., B Femandez, J.E. (1993) . Psychophysical fiequency for a gripping task. International Journal o f Industrial Ereonornics. 12,2 19-230.

Davis, P.J., & Femandez, J.E. (1994). Maximum acceptable frequencies for females performing a dnlling task in different wrist postures. Journal of Human Ereonomics. 23, 81-92.

De Clerq, C. et al. (1994) . Heel pad deformation during foot strike in ruming. Journal of Biomechanics. 27 (1 O), 1213-1232.

Derrick, T.R., Hamill, J., & Caldwell, G.E (1998) . Energy absorption of impacts during running at various &de lengths. Medicine Science and Soorts Exercise. 30 (l) , 128-135.

de Quervain, F. ( 1 895) . Veber eine form von chronischer tenonvaginitis. Corres~ondez- Blatt F. Schn-eizer Arzte, 25, 389.

Field. L.D., & Savoie, F.H. (1996) . Comrnon elbow injuries in sport. S ~ o r t s Iniurv Clinics.

Fernstrom, E.A.C., & Enckson, M.O. (1996) . Upper-arm elevation during office work. Eroonomics. 39 (1 O), 1221-1230.

Gescheider, G.A. (1985) . Psvchoohvsics: Method. Theorv. and Ao~iication (Znd ed.) . Hillsdale. N.J: Erlbaum Associates.

Gray, H. (1 893) . Anatomy. descriotive and surgical. (13' ed. ) . New York: Bounty Books.

Goldstein, S.A., Armstrong, T.A., Chaffin, DIB-, & Matthews, L.S. (1987) . Analysis of cumulative strain in tendons and tendon sheaths. Journal of Biomechanics. 29 (l), 1-6.

Habes. D., Carlson, W., Badger, D. (1985) . Muscles fatigue associated with repetitive arm lifts: effects of height, weight and reach- Er~onomics. 28 (Z), 471-488.

Hall, C. (1 997) . External pressure at the hand during object handling and work with tools. International Jounal of Industrial Ereonomics. 20, 191 -206.

Hatze. H. (1 992) . The effectiveness of grip bands in reducing racquet vibration transfer and slipping. Medicine Science and S ~ o r t s Exercise. 24 (2), 226-230.

Hennig. E. M., Rosenbaum, D., & Milani, T. L. (1992) . Transfer of tennis racket vibrations ont0 the human foreann. Medicine Science and S ~ o r t s Exercise, 24 (IO), 1 134-1 140.

Hennig, E.M., Milani, T.L., & Lafortune, M.A. (1993) . The use of ground reaction force parameters for the prediction of peak tibia1 accelerations in running. Journal of Ao~l ied Bionleclianics. 9, 306-3 14.

Higgs, P., Young, V.L., Seaton, M., Edwards, D., & Feely, C. (1992) . Upper extremity impairment in workers performing repetitive tasks. Plastic & Reconstructive Surcem. 90, 614- 630.

Howard, N. ( 1 937) . Pentendinitis crepitans. Journal of Bone and Joint Sur~erv. 19,447- 459.

Hooley, C.J., & McCrum, N.G. (1980) . The viscoelastic deformation of tendon. Joumal of biomechanics, 13, 521-528.

IEM Medical Technologies, Inc. (1999) . Questions & answers about sorbothane insoles. http://\x~v~v.bright.net/-iem/iemq.html.

James, S.L., Bates, B.T., & Osteniig, L.R. (1978) . Injuries to m e r s . American Journal of Sports Medicine. 6,40-50.

James, S .Lm, & Jones, D.C. (1 990) . Biomechanical aspects of distance running injuries. in P. R. Ca\-anagh (Ed.), Bioniechanics of Distance Running @p. 249-269). Champaign. IL: Human Kinetics Publishers.

Kanvowski, W., & Yates, J.W. (1986) . Reliability of the psychophysical approach to manual lifting of liquids by fernales. Ereonomics. 29,237-248.

Kim. C.H., & Fernandez, J.E. (1993) . Psychophysical fkequency for a drilling task. International Journal of Industrial Ergonomies. 12, 209-2 18.

Keir. P.J. , W e k , R.P., Ranney, D.A., & Lavery, W. (1997) . The effects of tendon load and posture on carpal tunnel pressure. The Joumal of Hand Sureew. 22a, 628-634.

budson , D.V. (1991) . Factors affecting force loading on the band in the tennis forehand. Joiirnal of Sports Medicine and Phvsical Fitness. 3 1,527-53 1.

Lafortune, M.A., & Lake, M.J. (1995) . H m a n pendulum approach to simulate and quanti fy locomotor impact loading. Journal of Biomechanics. 28 (9), 1 1 1 1 - 1 1 14.

Lafortune. M.A., Lade, M.J., & Hennig, E.M. (1996) . Differential shock transmission responses of the human body to impact severity and lower limb posture. Journal of Biomechanics, 29 (12). 1537-1537. -

Light. L.H., MacLellan, G.E., Kleneman, L. (1979) . Skeletal transients on heel strike in normal walking with different footwear. Journal of Biomechanics. 13,477-488.

MacLellan. G.E., Vyvyan, B. (1981) . Management of pain beneath the heel and achilles tendonitis u-ith visco-elastic heel inserts. Br J Sports Med. 15, 1 17-12 1.

Manske, P.R., Orgata, K., & Lesker, P.A. (1985) . Nutrient pathways to extensor tendons of primates. Journal of Hand Surgerv. 1 OB, 8-10.

Maylack, F.H. (1988) . Epidemiology of tennis, squash, and racquetball injuries. C h i c of Sports Medicine. 7,233-238.

McAtammey, L.. & Corlett, E.N. (1993) . RULA: a survey method for the investigation of work related upper limb disorders. Eraonomics. 24 (2), 91-99.

Miller. D.I. (1 990) .- Ground reaction forces is distance ninning. In P.R. Cavanagh (Eds.) , Biomechanics of Distance Rumine, (pp. 203-224) . Champaign, Illinois: Human Kinetics Publishers.

78

Mital. A.. Nicholson, AS., & Ayoub, M.M. (1993) . A euide to manual material handlino,. London; Taylor and Francis.

Moneirn, M.S. (1 992) . UInar nerve compression at the wrist. Hand Clinics. 8, (2), 337- 343.

Moore, A., Wells, R, & Ranney, D. (1991) . Quantimg exposure in occupational manual tasks with cumulative trauma disorder potential. Eraonomics, 1433- 1453.

Moore, J.S., & Garg, A. (1 995) . The strain index: a proposed method to analyze jobs for risk of distal upper extremity disorders. Amencan Industrial Association Journal. 56,443-458.

Munro, C.F., & Miller, D.I. ( t 987) . Ground reaction forces in mnning: a reexamination. Journal of Biomechanics. 20 (2), 147-155.

Nelson, NA. , Park, R.M., Silverstein, M.A., & Mirer, F.E. (1992) . Cumulative trauma disorders of the hand and wrist in the auto indusûy. American Journal of Public Health. 1 1 (82), 1550-1 552.

Ni_rg, B.M. (1 983) . Extemal force measurements with sport shoes and playing surfaces. In B.M. Nigg. & B.A. Kerr (Eds.) , The Proceedines of The International S m ~ o s i u m on Biornechanical As~ects of Sport Shoes and Plavine Surfaces Lpp 11-23) . Calgary: University of Calgary.

Nigg.. B.iM. (1 988) . The assessment of loads acting on the locomotor system in running and other sport activities. Seminars in Orthovaedics. 3 (4), 197-206.

Nigg, B.M. (1986) . Biornechanical aspects of running. In B.M. Nigg (Eds.) , Biomeclianics of Rumine Shoes (pp. 1-25) . Champaign, Illinois: Human Kinetics Publishers.

Nigg, B.M ., Bahlsen, H.A., Luethi,S.M., & Stokes, S. (1 987) . n i e influence of running velocity and nlidsole hardness on extemal impact forces in heel toe ruming. Journal of Biomechanics, 20 (1 O), 95 1-959.

NIOSH Technica! Report. (198 1) Work practices guide for manual lifting. DHHS (NIOSH) Publication 8 1 : 122.

Noe, D.A., Vote, S.J., Hoffman, M.S., Askew, M.J., & Gradisar, I.A. (1 993) . RoIe of the calcaneal heal pad and polymeric shock absorbers in attenuation of heel strike impact. Journal of Biomedical Engineering. 15 (l), 23-26.

Norkin, M., & Frankel, V.H. (1 989) . Basic Biomechanics of The Musculoskeletal Svstem. Philadelphia, PA: Lea & Febiger.

Orner, G.E. (1992) . Median Nerve Compression At The Wrist. Hand Clinics. 8 (2), 3 17- 323.

Plialen, G.S. (1966) . The carpal tunnel syndrome, seventeen years experience in diagosis and treatment of six hundred fi@-four hands. Journal of Bone and Joint Surnerv, 48, 2 1 1-228.

Pradas, M.M., & Callera, R.D. (1990) . Nonlinear viscoelastic behaviour of the flexor tendon of the human hand. Journal of Biomechanics. 23 (8), 773-781.

Paul.I.L.,Munro,M.B.,Aberneuiy,P.J.,Sirnon,S.R.,Radin,E.L.&Rose,E.M. (1978). Musculo-skeletal shock absorption: relative contributions of bone and soft tissues at various frequencies. Journal of Biomechanics. 1 1,237-239.

Pope, M.H., Magnusson, M., & Hansson, T. (1997) . The upper extremity attenuates intemediate frequency vibrations. Journal of Biomechanics. 30 (2), 103-1 08.

Potvin, J.P, & Chaing, J. (1998) . A psychophysical study to determine acceptable limits for tasks involving repetitive hand impacts (Report). Windsor, Ontario: University of Windsor, Occupational Biomechanics and Ergonomics.

Potvin. J.P., Fraser, D., & Murphy, M.P.H.J. (1999) . An evaluation of the hand impact set-erities associated with various trim installation tasks (Report). Windsor, Ontario: University of Windsor. Occupational Biomechanics and Ergonomics.

Radin. E.L. & Paul, I.L. (1 971) . The response of joints to impact loading. I- In vitro wear. -4rth. Rheum. 14, 356-362.

Radin. E.L. & Paul, I.L. (1970) . Does cartilage cornpliance reduce skeletal impact loads? Arth. Rlieum. 13, 139-144.

Radin, E.L., Paul, I.L., & Rose, R.M. (1 972) . Role of mechanical factors in pathogenesis of priinary osteoarthritis. Lancet (March 4), 5 19-52 1.

Radin, E.L., Parker, H.G., Pugh, J.W., Steinberg, R.S., Paul, I.L., & Rose, R.M. (1973). Response of joint to impact loading-III. Journal of Biomechanics. 6 , s 1-57.

Radwin, R.G., & Armstrong, T.A. (1985) . Assessment of hand vibration exposure on an assembly line. American Industrial Hvaiene Association Journal. 46 (2)- 2 1 1-2 19.

Ranny, D., Wells, R:, & Moore, A. (1995) . Upper limb musculoskeletal disorders in highly repetitive industries: precise anatomical physical findings. Ereonomics. 38 (7), 1408- 1423.

Robbins, S.E., Gouw, G.J., & Hanna, A.M. (1989) . Running-related injury prevention through impact rnoderating behavior. Med. Sci. Sports Exercise, 21, 130- 139.

Ross, P. (1994) . Ergonornic hazards in the workplace: assessrnent and prevention. AAOHN. 42 (4), 171-1 76.

Schuind, F., Cooney, W.P., Linscheid, R.L., An K.N., & Chao, E.Y.S. (1995) . Force and pressure transmission through the normal wrist. A theoretical two dimensional study in the posteroanterier plane. Journal of Biomechanics. 28 (S), 587-601.

Segesser, B. (1 985) . Sportverletningen und Sportschaden im Ellbogenbereich (Sports Injuries and Sports damage in the elbow region). Deutsche Zeitschnfi fur Sportmedizin. 3. 80-83.

Silverstein, B.A., Fine, L.A., & Armstrong, T.J. (1986) . Hand wrist cumulative trauma disorders in industry. British Joumal of Industrial Medicine. 43, 779-784.

Sil\,erstein, B.A., Fine, L A . , & Arnistrong, T.J. (1987) . Occupational factors and carpal tunnel syndrome. Arnerican Joumal of Industrial Medicine. 1 1, 343-358.

Silverstein, B.A., Fine, L.A., & Stetson, D. (1987) . Hand-wrist disorders among in~mestrnent casting plant workers. Joumal of Hand Sureerv. 12a (2 pt 2), 838-844.

Snook. S.H., & Irvine, C.H. (1967) . Maximum acceptabIe weight of Iifi. Arnerican Industrial Hveiene Association Joumal, 28, 322-329.

Snook. S.H., Irvine, CH., & Bass, S.F. (1970) . Maximum weights and workloads acceptabIe to male industrial workers. American Industrial Hveiene Association Joumal. 3 1, 579- 586.

Snook. S.H. (1971) . The effects of age and physique on continuous work capacity. Human Factors. 13,467-479.

Snook, S.H., & Ciriello, V.M. (1974) . Maximum weights and workloads acceptable to female workers. Journal of Occupational Medicine. 16, 527-534.

Snook, S.H. (1978) . The design of manual handling tasks, Ergonornics. 21,963-985.

Snook. S.H., & Ciriello, V.M. (1 991) . The design of manual handling tasks: revised tables of maximum acceptable weights and forces. Er~onomics. 34 (9), 1 197- 12 13.

Snook, S.H., Vaillancourt, D.R., Ciriello, V.M., & Webster, B.S. (1995) . Psychophysical studies of repetitive wrist flexion and extension. Ergonomics. 38 (7), 1488-1507.

Snook, S.H. (1985) . Psychophysical considerations in permissible loads. Ereonomics. 28 ( 1 ). 327-330.

Snook, S.H. (1987) . Approaches to the control of back pain in industry: job design, job placement. and educatiodtraining. Seine. 2,4559.

Sommerich, C.M., McGIothlin, J.D., & Manas, W.S. (1993) . Occupational risk factors associated with soft tissue disorders of the shoulder: a review of recent investigations in the li terature. Er~onomics, 36 (6), 697-71 7.

Sorbo thane Inc. ( 1 998) . Sorbothane online: performance characteristics. http://\.\s?x-.sorbothane.com

L'erbitsky, O., Minahi, J., Voloshin, A., Treiger, J., & Isakov, E. (1998) . Shock transmission and fatigue in hurnan ruming. Joumal of A ~ d i e d Biomechanics. 14, 300-3 1 1.

Voloshin, A. (1 986) . Biomechanical aspects of shock absorbing devices. Proceedings of NACOB Con ference, Montreal, 1 89-1 90.

Voloshin, A. & Wosk, J. (1982) . An in vivo study of low back pain and shock absorption in the human locomotor systern. Journal of Biomechanics. 15,2 1-27.

Webster, B.S.. & Snook, S.H. (1994) . The cost of compensable upper extremity cumulative trauma disorders. Journal of Occu~ational Medicine. 36 (7), 7 13-71 7.

Whi ting, W.C., & Zemicke, R.F. (1 998) . Biomechanics of Musculoskeletal Injury. Champaign. IL: Human Kinetics Publishing .

WSgiIB. Work Injuries 1988-1997. Report 2- 14.

Ziinmerman, N. B., Zimrnerman, S. I., & Clark, G. L. (1992) . Neuropathy In The Workplace. Hand Clinics. 8 (2), 255-262.

APPENDICES

Information and Consent Form

Ergonomîcs and Biomechanics Lab School of Human Kinetics

University of Windsor

Study Title: A Psychophysical Study To Determine Impact Maximum Acceptable Hand Impact Forces During Door Trirn Installation: Effects Of Hand Posture And impact Gloves

Conducted by: Marc Murphy (Master's studcnt) and Dr. J. R. Potvin (Supervisor) Phone: 252-2282 (Home) or 253-4232 cxt. 2452 (School)

1 agree to participate in a study that is dcsigned to add new knowledge concemhg rcpetitive impact Ioading of the hand during simulated trim assembly tasks using the palm and ulnar side of the hand. The investigator has explained the procedures and the necessary time cornmitment to me. 1 understand that 1 will be asked to perform repeated impacts using the hand, and sorbothane impact gloves in the palrnar and uhar hand positions. I will dererrnine the acceptable load magnitudes for each dynamic impact. 1 understand that the impact levels 1 select are to be performed continuously as if pan of full time employment. where 1 am required to strike the device at 5 repetirionsimin. with an impact at least sufficient to move the device through its full range of motion. Remember that thk is not a contest. Not ever-yone is expected to impact with the same amount of force. We want your judgment as to ho\\- much impact force is acceptable. m e procedure will require that I be trained for a rota1 of 4 houn (60 minutes for each of the four conditions). Al1 training will occur over two days and each 2- hr session will include a 15 min. rest period after 120 minutes. Data will be collected over the fmal 120 minutes of a third and final session (230 min). In each session 1 will be required to reset my selected resistance after every 15 min. were the researcher either increases or decreases the pressure by a randomly selected amount. Data collection will include rneasurin~ peaks. load rates. and impulse for both force and accelerations. Collection of the acceleration data will require subjt.cts ro n.ear a tvrist brace where an acceIerometer is attached to the back of the hand. Force data will be rnrasured. during impacts of the device. Throughout the study confidentiality will be placed on al1 information collçcted. 1 am aware that there is a possibility that during training and testing that 1 my feel discornfort or pain. but in ex i l session 1 wilI be free to increase and decrease the resistance to a b e l 1 fmd acceptable (resulting in no nunlbness or pain) and if discornfort persists I can terminate the study at any tune if 1 feel the need to do so.

Consent of Subject

1 have read and understood the information presented above for the procedures and risks involved in this study and have received satisfactory answers to questions reiated to this study. The specific details of this study have been expiained. i understand chat my identity will be protected throughout my participation in this study. 1 am aurare that 1 may report what 1 consider to be violations of my welfare to Dr. Bob Boucher 253-4232 ext. 2429 or the Office of Human Research. University of Windsor, and may withdraw from the study at any tirne. With full knowledge of al1 foregoing. 1 agree, of my ovm.free will. to participate as a subject in this study and to allow photographs andfor other data to be used for teaching or research presentations.

Signature: Date:

\\'itness: Date:

Appendix B

I a ~ l e m: 3uojecr anuuopomernc aara.

Subject

l 1 1 1 1 1

1 1 1 Male 1 181.13 1 192.50 1 23.25

Sex

1 2 3 4

1 1 1 Stdev 1 8.13 1 17.49 1 1.60

Large Medium Large Large

Dominant Hand I

Male Male Male Ma le

2.31 21.50

Stdev Female

5 6 7 8 9 10

184.0 185.0 183-0 180.0

1

Right Right Right Right

Glove Size lHeight(cm) 1

180.0 185.0 173.0 179.0 170.0 171.0

4.05 161 .O6

11 12 13 14 15 16

Male Male Male Male

Fernale Female

L

27.90 126.50

Weight (lbs)

21 5.0 160.0

155.0 240.0 185.0 200.0 120.0 140.0

Age

Female Female Female Female Female Fernale

25 21

21 23 26 25 21 24

Right Right Rig ht Rig ht Right Rig ht

Medium Large

Medium Medium Medium Medium

200.0 185.0

20 23 20 20 21 23

22.38 2.1 3

25 20

Right Right Right Right Right Left

129.0 130.0 160.0 11 3.0 105.0 1 15.0

159.50 40.84

Medium Medium Medium Small Small Small

Total Mean Stdev

167.5 161.8 158.8 157.0 147.5 155.0 171 -09 12.08

Appendix C

Table 1 C: Al1 mean and standard deviations for al1 dependent variables for each of the conditions look at within the cwrent study. Al1 standard deviation values are shown in brackets and bolded.

Dependent PK Force p Gender 1

Protection 1

( 123.8) Posture 1

i TTPK ' Force , (ma

5.2 ( 1 -0) 5.8

(1 -3)

5 -2 (1.0) 5 -8

(1.3)

5 -4 (1-3) 5.6

(1.1)

P a l n ~ 240.1 (1 14.2)

Force Impulse (N-s)

4.3 (1 -9) 2.7

(0.8)

3.3 ( W 3.8

(1 -8)

3.7 (1.8) 3 -3

(1 -5) Ulnar 254.3 1 (123.1)

PK Accel. ( m / s / s )

506.8 (1 40.7) 43 1.9

(147.7)

478.9 (1 43.3) 459.7

(1 54.2)

489.1 (151.3) 449.5

(144.1)

TTPK Accel. (ms)

5.7 (1 -7) 5.8

(2.0)

5 -4 (1-7) 6.0

(1 -9)

5.1 (1 -4) 6 -4

(2.0)

Accel. Impulse W s )

5 -9 ( 1-7) 4.9

(1.5)

5.5 (1.6) 5.4

(1 -8)

5.0 ( 1 3 5.9

(1 *8)

Appendix D

Table 1 D: Correlation coefficients between each of the variables measured. Values included the average values for each subject at each of the four impact conditions (bare palm, bare ulnar, glove palm, and glove ulnar).

Peak Force TTPK Force LR Force Force Impulse

Peak Accel. TTPK Accel. LR Accel. Accel. Impulse Resistance

Force Peak Force

1 .O0 -0.63

0.88 0.95

0.76

-0.06

0.50 0.82

0.72

77PK Force

1 .O0

-0.72 -0.56

-0.80

0.53

-0.72 -0.65

-0.55

LR Force

1.00 0.82

0.72

-0.19

0.53 0.53

0.81

Force Impulse

1 .O0

0.73

-0.1 7

0.53. 0.73

0.68

Accel. Peak A ccel.

0.66

TTPK A ccel.

-0.17

LR Accel.

1 .O0

-0 -40

0.84 0.82

A ccel. Impulse

1-00 0.54

1

1 .O0

-0.70 -0.08

0.48

1 .O0

0.55

Appendix E

The calculated impact arm effective masses for each subject.

1 Bare Hand 1 Glove Subjects

2 3 4 5 6 7 8

Mean

1

Palm 1 Ulnar 1

1 1 Total 1 0.45 t 0.53 I 0.51 1 0.58

0.43 0.56 0.59 0.72 0.56 0.51 0.33 0.52

Palm

0.50 0.60 0.80 0.87

UInar

0.53 0.56 0.71 0.86

0.58 0.53 0.90 0.90 0.47 0.62 0.51 0.67

0 -46 0.42 0.32 0.59

0.72 0.59 0.37 0.61

VITA AUCTORIS

NAME: Marc Patrick Henry Joseph Murphy

PLACE OF BIRTH: Val Caron, Ontario

YEAR OF BIRTH: 1974

EDUCATION: St. Charles College, Garson 1988-1993

University of Windsor, Windsor, Ontario 1993-1997 B.H.K.

University of Windsor, Windsor, Ontario 1997-1999 M.H.K.