The quick brown foxThe quick brown fox

Hand Intensive Work:

Predicting the Demand of a Manual Activity

Richard Wells

Department of Kinesiology, University of Waterloo

Hand Activities

Hold a hammer

Push hose on pipe

|| ?

Use a key to open a lock

Hold a plate of food

|| ?

Hand Strength

Characterizing human hand capabilities or demand created by occupational tasks has been mainly accomplished by measuring the maximum force exerted on a handgrip dynamometer or similar transducer.

How many people squeeze handgrip dynamometers at work?!!

Hand Grip Strength

If the occupational activity is: not a power grip or a pinch

on an isolated object or involves combinations of actions, such as exerting moments and forces,

how well does the handgrip dynamometer strength characterize the demand and load on the tissues of the hand and forearm?

Hand Prehension Description

Two Parts

1. The geometry of the hand/object interaction

2. The forces and moments applied on the environment

Y, MyY, My

Z, Z, MzMz

X, X, MxMxY, MyY, My

Z, Z, MzMz

X, X, MxMx

R. W

ells

Prehensile GripsCylindrical/Prismatic Grips Grips with Pulp/tip Contact

Non-Prehensile or Force Dependant “Grips”Hook “Press”

Palm Pulp Press, Thumb/Finger Tips 2/3/4/5,

Sphere `Tripod TipsKey/Lateral Pinch

Side Opposition Grip

A/B)

X)

T)

Y)

F)

K)J) E)

G)

R)

Z)Increasing force and size Decreasing Forces and Size

Increasing dexterity

Fingers 2/3/4/5 Carry Box

T+F)

X+F)K’)

M)

Typical Tool Use for Grip Types

A/B Pistol grip on in-line screw runner

T) Hammer (also T+F)

X) Carry or hold with small handles

Y) Pliers

Z) Screw-driver

J) Hold parts/objects

F) Key

K) Small prismatic objects

E) Small prismatic objects

K’) Pen, pencil, scriber, dental tool

G) Carrying with handle. Pull on wrench. Single finger(s) may operate trigger. Also carry boxes

M) Apply force, support tray, hand hammer

R) Sensory or apply force to seat or insert part

Part 2: Forces and Moments Exerted on Objects

Y, MyY, My

Z, Z, MzMz

X, X, MxMxY, MyY, My

Z, Z, MzMz

X, X, MxMxFF

External +Demand3Forces3Moments

Internal <=>Demand1 Force

Pressure <=>Distribution

Musculo-skeletal Tissue Loading(Internal Exposure/Dose Rate)

R. W

ells

R. W

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Wrench Defined

Exertion of hand on environment described by “wrench” (3 forces and 3 moments) expressed about the centre of the grip

Y, MyY, MyX, MxX, Mx

Z, MzZ, Mz

Y, MyY, My

X, MxX, Mx

Z, MzZ, Mz

R. Wells

Hand Actions

Because of the asymmetry of the hand there are 13 possible actions

Extend Ulnar Radial Supinate Pronate

Push Pull Push Up Push Down Push to Side Push to Side

Flex

Power Grip

Example: A Drilling Task

5 Nm Torque

1.2 kg. Mass

60N Feed Force

0-60

12.603.1-502

Wrench =

Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force

~0 >13%>7%17%33%~0%2%

Hand Relative Action Demand*

0-60

12.603.1-502

Wrench =

Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force

~0 >13%>7%17%33%~0%2%

0-60

12.603.1-502

0-60

12.603.1-502

Wrench =

Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force

~0 >13%>7%17%33%~0%2%

Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force

~0 >13%>7%17%33%~0%2%

Hand Relative Action Demand*

Measures of Hand Capabilities?

Most studies measure 1 or 2 of these components

Most studies use wrist moments or pinch/grip forces

No data on combined actions (e.g. pronate and pull)

ThereforeNeed to collect all forces and moments about centre of the grip

Measurement

Thirteen randomized actions, about the orthogonal axes in 3 grip types (power, lateral, and pulp pinch), as well as combined activities, were performed at maximal and sub-maximal levels in mid pronation and a naturally adopted wrist extension posture.

Measurement of CapabilitiesSpecially developed

dynamometer measured the three force and moment components as well as the pinch or power grip forces.

Population

Working men and women with recent manual work experience recruited from industrial temporary agency

Height

(m) Weight

(kg) Age

(years)

Grip Strength

(N) Females

(n=10) 1.59 70.6 33.4 302.0 SD 0.07 24.4 11.9 43.0

Males (n=10) 1.78 82.3 32.7 450.0 SD 0.07 15.2 11.3 60.0

Example Data

Maximum Moments about Grip Centre:

Moment N.m (SD) Pronator Supinator

Radial Deviator

Ulnar Deviator Extensor Flexor

Female 4.7 (1.7) 4.9 (1.6) 6.2 (2.7) 7.7 (1.9) 6.2 (1.8) 7.1 (2.3) n 10 10 10 10 10 10

Male 8.1 (2.3) 8.0 (1.9) 10.3 (3.5) 13.0 (4.2) 8.2 (1.7) 9.3 (2.0) Power Grasp

n 10 10 9 9 8 8

Female 1.9 (0.6) 2.2 (1.0) 2.0 (0.6) 1.1 (0.2) 0.8 (0.3) 0.9 (0.4) n 9 9 8 8 8 8

Male 3.8 (1.1) 3.5 (0.8) 3.0 (1.1) 1.7 (0.5) 0.9 (0.3) 1.3 (0.6) Lateral Pinch

n 10 10 9 9 9 9

Female 1.3 (0.4) 1.9 (0.7) 1.1 (0.6) 2.0 (0.9) 1.8 (0.7) 1.5 (0.5) n 10 10 9 9 10 10

Male 2.2 (0.4) 2.4 (0.8) 1.7 (0.3) 2.6 (0.9) 2.6 (0.8) 2.1 (0.6) Pulp

Pinch n 9 10 9 8 10 10

Electromyography (EMG)

8 Sites

EMG/RPE vs Exertion

Lateral Pinch, One Participant, All Muscles

0

0.2

0.4

0.6

0.8

1

-200 -100 0 100 200

Push N Pull

Pro

po

rtio

n o

f M

axim

um

ECU

ED

ECR

FDI

FCU

FCR

FDS

FPL

RPE

Max limited by balance, shoulder strength?

EMG/RPE vs Exertion

Pulp Pinch, One Participant, All Muscles

EMG/RPE vs Exertion

Power Grip, Flexor Carpi Ulnaris, All Participants

Hand Demand Calculator

Analysis Calculator

20 Participants10 M 10 F

Multiple Linear Regression by ParticipantEMG1 = f (3 x Force, 3 x Moment)EMG2 = f (3 x Force, 3 x Moment)…..EMG8 = f (3 x Force, 3 x Moment)RPE = f (3 x Force, 3 x Moment)

Regression Coefficients

3 x Force, 3 x MomentPercentile of population

Predicted;8 EMG and RPE

Hand Demand Calculator: 1

Hand Demand Calculator: 12

Does The Method Describe the Demand on the Hand?

Compare the perceived exertion and EMG for an action and the same action described as a wrench and performed on the test apparatus

=

0-60

12.603.1-502

Wrench =

Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force

~0 >13%>7%17%33%~0%2%

Hand Relative Action Demand*

0-60

12.603.1-502

Wrench =

Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force

~0 >13%>7%17%33%~0%2%

0-60

12.603.1-502

0-60

12.603.1-502

Wrench =

Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force

~0 >13%>7%17%33%~0%2%

Fx Palmar/VolarFy Pull/PushFz Radial/UlnarMx Ulnar/RadialMy Pron/SupinatorMz Flexor/ExtensorFgrip Grip/Pinch force

~0 >13%>7%17%33%~0%2%

Hand Relative Action Demand*

Test Tasks 1

Test Tasks 2

EMG for Tasks and Their Mock-Ups

Extensor Digitorum

Slope = 1.042 R2= 0.93

RPE for Tasks and Their Mock-UpsPerceived Exertion

Slope = 1.11 R2= 0.929

The Wrench Demand Description

The wrench demand description appears to adequately describe the demand on the forearm hand system

Two new grips added, “”volar diagonal” and three finger “tripod” pinch

Adding these grips to the “Calculator”

How to make the technique available?As part of “Ergowatch”?

Web available calculator?

Current and Future Work

Summary

Existing methods of hand demand evaluation were deemed inadequate

A description of hand activities was developed that accounts for the demand of a manual activity

Experimental testing of working Canadian men and women while performing a wide range of hand activates allowed creation of relationships between the external task definition and its demand

A “ hand demand calculator” was developed for evaluation and design

References

1. Wells, R. and Greig, M. Characterising human hand prehensile capabilities by force and moment wrench, Ergonomics, 15;44(15):1392-402, 2001.

2. Greig, M. and Wells, R. (2004) Measurement Of Prehensile Grasp Capabilities By A Force And Moment Wrench: Methodological Development And Assessment Of Manual Workers, Ergonomics, 47(1); 41-58..

3. Morose, T., Greig, M., and Wells, R. (2004) Utility of using a force and moment wrench to describe hand demand, Occupational Ergonomics, 4:1-10.