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The Relationship Between Relative Muscular Strength and Joint The Relationship Between Relative Muscular Strength and Joint
Mobility in Firefighters Mobility in Firefighters
Samuel C. Nozicka Eastern Illinois University
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THE RELATIONSHIP BETWEEN RELATIVE MUSCULAR STRENGTH AND JOINT
MOBILITY IN FIREFIGHTERS
Samuel C. Nozicka B.S.
Eastern Illinois University, 2020
Department of Kinesiology, Recreation and Sport
Eastern Illinois University
Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in
Exercise Physiology
i
Abstract
The Relationship Between Relative Muscular Strength and Joint Mobility in Firefighters
Samuel C. Nozicka
Firefighters job requirements consist of running upstairs, climbing ladders, ceiling breach
and pull, carrying equipment, forcible entry, dragging hoses, raising ladders, and rescue of
patrons all while wearing heavy protective equipment that limits their mobility (Park et al.,
2015). The purpose of this study was to examine the relationship between relative strength
and mobility within the population of firefighters. The subjects were volunteers consisting of
twelve male firefighter ranging in age from 25-52 with the mean age of 37.7 7.7 years.
Leighton Flexometer was used to measure joint range of motion (ROM) in different active
movement patterns (Leighton, 1966). Absolute strength was evaluated using a 5RM estimate
of 1RM (Haff & Triplett, 2016; Shephard, 2009) for the back squat, conventional deadlift,
pull up, and bench press. Relative strength was calculated for each of the movement patterns
by dividing the subjects 1RM by their bodyweight Baechle & Earle, 2008; Dohoney et
al.,2002; Haff & Triplett, 2016; Shephard, 2009). The relationship between relative strength
and joint mobility in firefighters showed negative correlations indicated that increased
plantar flexion ROM could lead to decrease in relative strength ratios in both the back squat
r(9) = -.66, p=-.026 and conventional deadlift r(9) = -.61, p=-.036. A positive correlation
that was increased shoulder flexion ROM could lead to increase relative strength ratio in the
back squat r(9) =.70, p=.017. It was concluded that increased joint mobility does not illicit
increased relative strength in firefighters except in specific joints and exercises. Shoulder
flexion ROM correlated with increased relative strength of the back squat in firefighters was
the one exception to the findings of this study. Firefighters sample size was too small to
ii
entirely understand the relationship. The relationship between relative strength and joint
mobility in firefighters needs to be further investigated.
iii
Acknowledgements
Sincere appreciation and gratitude is given to each member of the Charleston, Illinois
Fire Department for contributing for their time and energy toward this study.
I would also like to thank every member of my committee for their contributions to
the success of this thesis. First off, I would like to thank Dr. Pritschet for helping me through
this process as the chair of my committee. I would also like to thank Mrs. Maranda Schaljo
for facilitating the connection with the fire department and all the time spent during the
recruitment process. I would like to thank Mr. Joshua Stice for all of his help through this
process.
I would also like to thank all of my friends and family who have helped me get
through the stress of this thesis. I would not be able to achieve everything that I have
without the help from my wonderful mother Geri Nozicka and amazing father Steve
Nozicka. I owe you all and love you all so much.
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Table of Contents
CHAPTER I ............................................................................................................................. 1
INTRODUCTION .................................................................................................................... 1
Purpose of Study .................................................................................................................. 4
Hypothesis ............................................................................................................................ 4
Limitations of the Study ....................................................................................................... 4
Significance of Study ........................................................................................................... 5
CHAPTER II ............................................................................................................................ 6
REVIEW OF RELATED LITERATURE ............................................................................... 6
Forms of Strength ................................................................................................................. 6
Relative Strength .................................................................................................................. 8
Strength Testing ................................................................................................................. 13
Mechanisms of Relative Strength ...................................................................................... 15
Joint Mobility and Association with Strength .................................................................... 19
Functional Movement Screen ............................................................................................. 20
Firefighters Needs Analysis ............................................................................................... 22
Literature Review Conclusions .......................................................................................... 25
CHAPTER III ......................................................................................................................... 28
METHODOLOGY ................................................................................................................. 28
Participants ......................................................................................................................... 28
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Recruitment Procedures ..................................................................................................... 28
Equipment .......................................................................................................................... 29
Leighton Flexometer .......................................................................................................... 29
Procedures .......................................................................................................................... 30
Analysis .............................................................................................................................. 32
CHAPTER IV ........................................................................................................................ 34
RESULTS ............................................................................................................................... 34
Subjects .............................................................................................................................. 34
Health History Questionnaire ............................................................................................. 35
Joint Mobility ..................................................................................................................... 38
Firefighters Absolute Strength Results .............................................................................. 48
Firefighters Relative Strength Results ................................................................................ 54
CHAPTER V .......................................................................................................................... 70
DISCUSSION ........................................................................................................................ 70
Relative Strength and Joint Mobility ................................................................................. 70
Absolute Strength and Joint Mobility ................................................................................ 75
CHAPTER VI ........................................................................................................................ 79
SUMMARY AND CONCLUSION ....................................................................................... 79
Summary of Findings ......................................................................................................... 79
Conclusion .......................................................................................................................... 80
Recommendations for Future Studies ................................................................................ 80
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WORKS CITED ..................................................................................................................... 81
APPENDICES ...................................................................................................................... 103
APPENDIX A-Informed Consent Form .......................................................................... 103
APPENDIX B- Health History Questionnaire ................................................................. 107
APPENDIX C-Recruitment Flyer .................................................................................... 111
vii
List of Tables
TABLE 1 .................................................................................................................................. 36
TABLE 2 .................................................................................................................................. 38
TABLE 3 .................................................................................................................................. 48
TABLE 4 .................................................................................................................................. 61
TABLE 5 .................................................................................................................................. 66
viii
List of Figures
FIGURE 1 ................................................................................................................................. 37
FIGURE 2 ................................................................................................................................. 40
FIGURE 3 ................................................................................................................................. 41
FIGURE 4 ................................................................................................................................. 42
FIGURE 5 ................................................................................................................................. 43
FIGURE 6 ................................................................................................................................. 44
FIGURE 7 ................................................................................................................................. 45
FIGURE 8 ................................................................................................................................. 46
FIGURE 9 ................................................................................................................................. 47
FIGURE 10 ............................................................................................................................... 49
FIGURE 11 ............................................................................................................................... 50
FIGURE 12 ............................................................................................................................... 51
FIGURE 13 ............................................................................................................................... 52
FIGURE 14 ............................................................................................................................... 53
FIGURE 15 ............................................................................................................................... 55
FIGURE 16 ............................................................................................................................... 56
FIGURE 17 ............................................................................................................................... 57
FIGURE 18 ............................................................................................................................... 58
FIGURE 19 ............................................................................................................................... 59
FIGURE 20 ............................................................................................................................... 62
FIGURE 21 ............................................................................................................................... 63
FIGURE 22 ............................................................................................................................... 64
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FIGURE 23 ............................................................................................................................... 67
FIGURE 24 ............................................................................................................................... 68
FIGURE 25 ............................................................................................................................... 69
x
Definition of Terms
ROM: Range of Motion
Joint Mobility: The degree to which an articulation can move before being restricted by
surrounding tissues.
Muscular Strength: The muscles ability to exert maximal force in one contraction.
Relative Strength: The total amount of force that can be produced in a movement, relative to
one’s bod weight.
Absolute Strength: the maximal amount of force that can be produced in a single movement.
Repetitions: The number of times one complete motion of an exercise is completed
consecutively.
1RM: The maximal amount of weight that can be moved for one repetition only.
5RM: The maximal amount of weight that can be moved for five repetitions only.
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CHAPTER I
INTRODUCTION
The most precise definition of strength is the maximal ability to exert force under a
given set of conditions defined by body position, the body movement by which force is
applied, movement type (concentric, eccentric, isometric, plyometric) and the movement
speed (Everett, 1993; Gerstner et al., 2018). There are two ways in which strength can be
expressed –as absolute strength or as relative strength. The difference between the two types
is that absolute strength is the maximum amount of force exerted, regardless of muscle or
body size (Hicks et al., 2012). Greater amounts of absolute strength favor those with higher
bodyweights (Andersen et al., 2018). Relative strength is the amount of strength compared
to the size of the individual’s bodyweight (force per unit of body weight) (Clemons, 2014).
This represents an individual’s ability to move their body through space (Ronai & Scibek,
2014). Adequate relative strength is important to successful athletic performance as well as
performance of activities of daily life (Baechle & Earle, 2008).
Range of motion is defined as the extent of movement in a joint or series of joints
measured in degrees of a circle (Park et al.,2015; Median McKeon & Hoch, 2019). Range of
motion can also be expressed in two different forms–flexibility and mobility (Park et al.,
2015). Mobility is the ability of a joint to move actively through a range of motion (Median
McKeon & Hoch, 2019). Whereas, flexibility is the ability of a muscle or muscle group to
lengthen passively through a range of motion (Haff & Triplett, 2016). Both are important for
enhancing physical performance but it is mobility that has the most impact as it is the active
joints range of motion that is utilized frequently in tasks that are performed.
2
A Firefighter’s job requirements can include running upstairs, climbing ladders,
ceiling breach and pull, carrying equipment, forcible entry, dragging hoses, raising ladders
and extension, and rescue of patrons all while wearing heavy protective equipment which
limits their mobility (Park et al., 2015) all firefighters must pass a physical exam in order to
be eligible for the job. This exam is called the Candidate Physical Ability Test (CPAT).
To become a firefighter all firefighters must pass a physical exam. This exam is
called the Candidate Physical Ability Test (CPAT). The CPAT was developed after years of
research and input from an international committee comprised of the International
Association of Fire Fighters (IAFF) and International Association of Fire Chiefs (IAFC)
members. This test was jointly created to be the standard physical test for recruit candidates
who are seeking to join fire departments in North America (Williams et.al., 2009. The test
requires firefighter to candidates to engage in the following activities ceiling breach and
pull, equipment carry, forcible entry, hose drag, ladder raise and extend, rescue, search, and
stair climb. All of these exercises must be completed in less than 10 minutes and 20 seconds.
Candidate success is measured on a pass/fail basis. Throughout the CPAT, candidates wear a
hard hat, gloves, and a 50-pound vest to simulate the weight of a self-contained breathing
apparatus and firefighter protective clothing (Lane et.al., 2019; Williams et.al., 2009). All of
these tasks require a minimum absolute strength regardless of the firefighter’s size, having
to perform these duties in heavy protective equipment that limits their range of motion
(Peterson et al.,2008; Park et al., 2015; Coca et al., 2015; Orr et al., 2019).
In addition to strength, mobility among fire personnel while on and off duty is
essential for their safety. The Los Angeles Fire department states that a firefighter’s ability
to maximize range of motion at a given joint while maintaining active muscular control on a
3
joint to redirect force and control movement in the presence of normal muscle flexibility and
joint mobility is a key to success while fighting fires and in everyday life (Sanko et. al,
2020). Considering the kinetic chain, if the body is not able to perform a movement with
proper form, it will compensate with a poor movement elsewhere. This can cause undesired
negative issues in the body while on duty (Sanko et. al., 2020).
Determining the relationship between relative strength and mobility in the population
of firefighters may provide the insight to improve performance, prevent injuries and
fatalities. Most firefighting injuries occur to the back and the shoulders (Phelps et.al., 2018).
Firefighters injuries annually in the United Sates add up to a cost of $2.8 to $7.8 billion
dollars (Sanko et.al., 2020). Non-optimal movement patterns, mobility imbalances, and
muscular imbalances can lead to injuries while on duty. The National Fire Protection
Association published a study stating that injuries to the trunk possibly caused by lack of hip
mobility are prominent among firefighter’s injury occurrences (Orr et al., 2019). With this
knowledge, training programs for firefighters can be refined to meet their specific needs
(Smith, 2011; Windisch, 2017). Helping firefighters to be more physically fit for duty
creates safer communities for everyone.
Few studies in the current literature have examined the relationship between relative
strength and mobility in firefighters. Some research discusses absolute strength in this
population but did not examine relative strength (Sheaff et al., 2010; Perroni et al., 2015). In
the literature studies reference muscular strength defined as the ability to carry out work
against a resistance and the maximal force produced against a load, is studied in firefighters
without regard to the relative strength of the individual (Everett, 1993; Gerstner et al., 2018;
Häkkinen et al., 2003). Relative strength is particularly important because the weight of their
4
Personal Protection Equipment (PPE) typically weighs 45 pounds or more (Lackore, 2007).
Additionally, firefighters may also carry a thermal imaging camera, radio, box light,
Halligan bar and an axe which may exceed 72 total extra pounds they have to carry
(Lackore, 2007). Firefighters have to carry equipment that can represent as much as 20%-
40% of their body weight when responding to fire calls (Lackore, 2007). The PPE that
firefighters wear has been shown to reduce lower body range of motion in the sagittal and
transverse planes (Coca et al., 2015; Park et al., 2015; Orr et al., 2019) while increased
passive range of motion has been shown to be associated with increased isometric and
concentric force. With PPE that firefighters wear being restrictive of their joint mobility and
substantially demanding on their relative strength, firefighters must have superior joint
mobility and enhanced relative strength in order to be able successfully complete task of
their job requirements.
Purpose of Study
The purpose of this investigation was to identify the relationship between relative muscular
strength and joint mobility in firefighters.
Hypothesis
It was hypothesized that those firefighters with increased mobility would have a greater
relative strength; conversely, the firefighters who have decreased mobility would also have
lower relative strength.
Limitations of the Study
There were a few unavoidable limitations to this study. The subjects were all
volunteers and were not randomly selected. The subjects of this study were all fireman from
5
only one fire department in mideastern Illinois. The demographic of these fireman was
minimally diverse with all of the participants being males and all from a single race
(Caucasian). Additionally, many of the subjects were untrained and have had no background
in strength training.
Significance of Study
The present study investigated the relationship between relative strength and joint
mobility in male firefighters. Few studies have examined the relationship between relative
strength and mobility in firefighters. Most research is focused on absolute strength in this
population but did not examine relative strength or mobility. Relative strength is an essential
element to a firefighter’s daily work because of the weight of the restrictive gear they carry
and wear when fighting fires.
6
CHAPTER II
REVIEW OF RELATED LITERATURE
The purpose of this investigation was to identify the relationship between relative
muscular strength and joint mobility in firefighters.
This review of related literature was organized into the following major headings:
forms of strength, relative strength, strength testing, mechanisms of relative strength, joint
mobility and association with strength, functional movement screening, and firefighters need
analysis.
Forms of Strength
There are four forms in which to express strength. These four forms are absolute
strength, strength endurance, power or explosive strength and relative strength (Dirnberger
et.al., 2012; Sökmen et.al., 2018). To be able to know how relative strength affects mobility
one must understand the differences in these forms of strength.
Absolute strength and maximal strength are terms that can be used interchangeably.
The absolute or maximal strength of a muscle or a group of muscles in a given movement
equals the highest external resistance an athlete can overcome or hold with full voluntary
mobilization of his or her neuromuscular system (Lyakh et.al., 2014). This means it is the
absolute greatest amount force that one can produce for one repetition at a single point in
time. This is also known as a one repetition maximum (1RM). The 1RM test is often
considered as the ‘gold standard’ for assessing the strength capacity of individuals in non-
laboratory environments (Levinger et.al., 2009). The 1RM test is most commonly used by
7
strength and conditioning coaches to assess strength capacities, strength imbalances, and to
evaluate the effectiveness of training programs (Braith et.al., 2009).
Explosive strength is the speed at which you can use your strength. It involves heavy
loading during shorter high speed movements for lower repetition ranges with long intervals
between sets (Taylor & Beneke 2012; Turner & Jeffreys, 2010). Explosive strength
primarily involves the Rate of Force Development (RFD). The RFD is a measure of
explosive strength, or how fast an athlete can develop force. This is defined as the speed at
which the contractile elements of the muscle can develop force (Aagaard et. al., 2002).
Therefore, improving an athlete’s RFD may make them more explosive as they can develop
larger forces in a shorter period of time. In fact, higher RFDs have been directly linked with
better jump, sprint cycling, and weightlifting (Haff et.al., 2005; Kawamori et.al., 2006;
Laffaye et.al., 2013; Laffaye et. al., 2014; Nuzzo et. al, 2008; McLellan et. al, 2011; Stone
et.al., 2004; Slawinski et.al., 2010). The rate at which force can be produced is considered a
primary factor to success in a large variety of sporting events (Stone et.al., 2002). Explosive
strength benefits dynamic movements such as jumping bounding, punching, sprinting, and
change of direction. Being able to move loads quickly through space and time increases your
force output, thus making movement more dynamic and capable of producing greater force
(Aagaard et.al., 2002; Andersen & Aagaard, 2006).
Strength endurance is the ability to repeatedly exert sub-maximal force against a
form of resistance. It is displayed in activities that require a relatively long duration of
muscle tension with a minimal decrease in efficiency (Hughes et. al., 2018; Walker et.al.,
2017). Strength endurance movements require situations in which a high level of muscle
endurance is exhibited with examples of this such as hill sprints, sled pushes, high volume
8
weightlifting sessions, etc. Strength endurance is ultimately lower loads moved repeatedly
by a muscle (Menz et.al., 2019).
Relative strength is the maximal amount of strength in a movement compared to
one’s body size or weight. Relative strength is how strong someone is compared to their
bodyweight (Case et.al., 2020). Relative strength and absolute or maximal strength are
related. When relative strength increases so should absolute strength unless the individual’s
body weight increases. Relative strength is vital for sporting tasks such as gymnastics,
wrestling, weightlifting etc. Sporting events that require weight classes or bodyweight
control require high amounts of relative strength. Additionally, movement patterns such as
pull ups require relative strength (Johnson et.al., 2009).
Relative Strength
Relative strength is a topic in the literature that has been researched but not as
extensively as other forms of strength. Case et al., (2020), investigated the efficacy of using
the relative strength of Division I athletes in the 1RM back squat as an identifier of seasonal
lower extremity injury. In this study, the participants were from the sports of football,
women’s volleyball and softball with a total of seventy-one athletes. Forty-six of them were
male football players and 25 of them were female in either volleyball or softball (Case et.al.,
2020). The 1RM back squat was measured in kilograms and the reported injuries were
collected. The results showed that relative strength in the back squat was significantly lower
in injured athletes versus uninjured athletes in both men and women (Case et.al., 2020). The
data from this study may indicates that increased relative strength can serve as a tool to
predict injury risk in collegiate athletes (Case et.al., 2020). If increased relative strength in
9
the back squat can lead to less injuries in various collegiate sports, then it could possibly
also lead to similar results in tactical athletes such as firefighters.
Instead of relative strength being a predictor of injury it can also be a predictor of
athletic performance. Andersen et. al., (2018) investigated the relationship of absolute and
relative lower body strength to predictors athletic performance among Division II collegiate
female soccer players. In this study the soccer players were assessed for performance in the
vertical jump, 3RM back squat, 505- agility, modified T-test, 10 m and 30 m sprint, and 20
m multistage fitness test (20 m MSFT). Relative strength was calculated based on the
estimated 1RM back squat divided by the athlete’s body weight (Andersen et. al., 2018).
The results of the testing showed significant correlation between relative lower body
strength and vertical jump, 505 agility test, modified T-test, 10 m and 30 m, and the 20 m
MSFT (Andersen et. al., 2018). The findings of this study may indicate that strength and
conditioning coaches should emphasize their players to improve the player’s power, agility,
and speed performance in their respective sports.
Furthermore, relative strength has been shown to have a correlation with
countermovement jump performance, multi-joint isomeric and dynamic strength tests.
Nuzzo et.al., (2008) investigated the relationship between countermovement vertical jump
(CMJ) performance and various methods of multi-joint strength tests (Nuzzo et.al., 2008).
This study used collegiate athletes in the sports of football and track and field. Measures of
the 1RM in the back squat and the power clean were recorded in the first testing session.
The second session consisted of the assessment of peak force (N), relative peak force (N x
kg-1), peak power (W), relative peak power (W x kg-1), peak velocity (m x s-1), and jump
height (meters) in a CMJ, and peak force and (RFD) (N x s-1 ) in a maximal isometric squat
10
(ISO squat) and maximal isometric mid-thigh pull (ISO mid-thigh) were assessed (Nuzzo
et.al., 2008). The findings of this study showed significant correlations between relative
1RM’s in both the squat and the power clean, to relative CMJ peak power, CMJ peak
velocity, and CMJ height. The study also found that there was no significant correlation
between the four measures and absolute strength (Nuzzo et.al., 2008). These results show
that increasing maximal relative strength can improve explosive lower body movements
optimizing lower body power (Nuzzo et.al., 2008). Therefore, increased relative strength,
rather than increased absolute strength, leads to increased performance.
Relative strength has been demonstrated to increase athletic performance. The
relationship between relative maximal strength and sprint and jumping performance has
been examined at different competitive levels of athletics. A study was conducted to
determine whether relative maximal strength correlates with sprint and vertical jump height
in elite male soccer players (Wilsoff et.al., 2004). This study involved international male
soccer players with a mean age of 25.8 years. The researchers tested maximal relative
strength in half squats and sprinting ability with the 0-30 meter and the 10-meter shuttle run.
Vertical jump was also assessed (Wilsoff et.al., 2004). The findings of this study indicated
that there was a strong correlation between relative maximal strength in half squats and
sprint/ jump performance. Improving maximal relative strength in lower body movements
such as the squat was shown to increase performance. They also state that elite soccer
players should focus on maximal strength training, with an emphasis on maximal
mobilization of concentric movements (Wilsoff et.al., 2004). This study suggested that
enhanced joint mobility will lead to improvements in athletic performance, indicating that
improving joint mobility may illicit increases in relative strength.
11
Relative strength and the maximal rate of RFD are intertwined. Aagaard et.al.,
(2002) examined the effect of resistance training on contractile RFD and efferent motor
outflow “neural drive” during maximal muscle contraction. Contractile RFD (slope of force-
time curve), impulse (time-integrated force), electromyography (EMG) signal amplitude
(mean average voltage), and rate of EMG rise (slope of EMG-time curve) were determined
(1-kHz sampling rate) during maximal isometric muscle contraction (quadriceps femoris)
(Aagaard et.al., 2002). The subjects of this study consisted of fifteen male volunteers who
had not previously participated in systematic resistance training. The training portion of this
study consisted of progressive heavy-resistance strength training for 14 weeks for a total of
38 sessions (Aagaard et.al., 2002). Obligatory leg training exercises included hack squats,
incline leg press, isolated knee extension, hamstring curls, and seated calf raises. Four
(weeks 1–10) or five (weeks 11–14) sets were performed for each exercise. Training loads
ranged between 3 repetitions maximum (RM) and 10 RM, except for the first 10 days (4
sessions), when lower loading was used (10–12 RM). Very heavy loadings (4–6 RM) and
increased number of sets (ensuring unchanged total workload) were used in the final 4
weeks of the study (Aagaard et.al., 2002). Contractile rate of force development (RFD) was
defined as the slope of the moment-time curve derived at time intervals of 0–30, 0–50, 0–
100, and 0–200 ms relative to the onset of contraction (Aagaard et.al., 2002). Increases in
peak isometric moment were observed post training in parallel with a steeper slope of the
moment-time curve in the early time phase of muscle contraction. The increase in slope was
reflected by a significant increase in contractile RFD, which was observed both in the initial
(30 and 50 ms) and later (100 and 200 ms) phases of force rise (Aagaard et.al., 2002). The
results indicated that relative strength and peak force production show a linear relationship.
12
The results of this study show that increases in peak force production capabilities can lead to
increases in relative strength ratios. Increased peak force production capabilities can have
similar effects that relative strength will on mobility.
To continue on, the linear relationship between peak force production and mobility
has been studied recently. Talukdar et.al., (2015) investigated the effects the peak force
production and mobility have on cricket ball throwing velocities. In the study, 11
professional cricketers and 10 under-19 club-level cricketers performed the chop and lift,
seated and standing cricket ball throw, seated and standing side medicine ball throw, and
seated active thoracic rotation range of motion (ROM) and hip rotation ROM on one
occasion. It was concluded that greater ROM at proximal segments, such as hips and
thoracic, can be useful in transferring the momentum from the lower extremity in an
explosive task such as throwing (Talukdar et.al., 2015). The findings of this study showed
that increased joint mobility may improve peak force production capabilities. The linear
relationship between peak force production capabilities and relative strength shown by
Aagaard et.al., (2002) and the linear relationship between peak force production and
mobility shown by Talukdar et.al., (2015) may illicit this similar linear relationship between
relative strength and joint mobility. The age of the participants in this study can be
comparable to the age of firefighters because the age of the cricket players was 23.8 ± 2.27
years, with firefighters ages ranging from 22 to 54 years (Lusa et.al., 1994; Talukdar et.al.,
2015).
13
Strength Testing
The assessment of the 1RM is used to measure maximal strength capacities, it can
also be used to measure force-time, power-time, and velocity-time characteristics when
performed using specialized equipment such as a force plate. As strength is an essential
component in day-to-day life and in sports performance, optimizing an athlete’s strength
capacity is often very beneficial (Comfort et. al., 2014; Sander et.al., 2013; Wisløff et. al.,
2004). One repetition maximum testing is a useful assessment before and after a prescribed
training program to evaluate the effectiveness of the program. One’s ability to abdominally
brace the trunk during a 1RM attempt can help to prevent injury (Norrie & Brown, 2020).
Inability to brace properly can cause a loss in spinal stiffness during max attempt which can
result in injury during 1RM attempt (Schoenfield et.al., 2015). Heavy weights can place
significant strain on joints and connective tissues; therefore, over time, subjecting athletes to
maximum or near-maximum loads may lead to breakdowns, tendinitis, sore joints, and
injury (Stone, 1998). The goal in training for maximal strength is to prime the nervous
system to recruit as many motor units as possible for a single, all-out effort (Grgic et.al.,
2020).
Crewther et.al., (2008) investigated free hormone (in saliva) responses to squat
workouts performed by recreationally weight-trained males, using either a power (8 sets of 6
reps, 45% 1 repetition maximum [1RM], 3-minute rest periods, ballistic movements),
hypertrophy (10 sets of 10 reps, 75% 1RM, 2-minute rest periods, controlled movements), or
maximal strength scheme (6 sets of 4 reps, 88% 1RM, 4-minute rest periods, explosive
intent). The maximal strength scheme elicited the highest levels of salivary testosterone and
14
cortisol showing that acute hormonal responses to resistance exercise contribute to protein
metabolism. Then load volume may be the most important workout variable activating the
endocrine system and stimulating muscle growth (Crewther et.al., 2008). The results of this
study showed that a percentage closer to one’s 1RM will produce more cortisol release
within the body. Which indicates that a 1RM protocol will induce more central nervous
system stress compared to a multi-repetition maximum protocol.
Furthermore, safer alternatives to the 1-RM strength tests, are multiple repetition
maximum (M-RM) strength tests (Baechle & Earle, 2008; Hopkins, 2000). The M-RM is
defined as the maximal weight which a person can lift over a specified number of repetitions
with the correct lifting technique (Baechle & Earle, 2008). For instance, the 5-repetition
maximum (5-RM) is the maximal weight which a person can lift five times with the correct
lifting technique. The M-RM strength test can be used for the same purposes as the 1-RM
strength test. Furthermore, the M-RM strength test is qualified for prescribing the intensity
for strength training (Taylor & Fletcher, 2012). Beyond this, the M-RM can be used as a
predictor of the 1-RM. In particular, the 5-RM allows a valid estimation of the 1-RM
(Baechle & Earle, 2008; Dohoney et.al., 2002; Reynolds et.al., 2006).
Grgic et al., (2020) demonstrated that the 1RM is a valid assessment for strength
testing. They reviewed studies that investigated the reliability of the 1RM test of muscular
strength and summarize their findings. The systematic review searched for studies were
conducted through eight databases. Studies that investigated test-retest reliability of the
1RM test and presented intra-class correlation coefficient (ICC) and/or coefficient of
variation (CV) were included. This review examined 32 studies in the current literature. The
result showed that the 1RM was reliable in trained and untrained individuals after
15
familiarization sessions (Grgic et.al.,2020). The results of this study demonstrated that 1RM
strength testing was reliable and validated for assessments of strength in trained populations.
This could indicate without familiarization sessions that a multi-repetition maximum was
comparable to a 1RM protocol.
Additionally, Gail & Kunzell, (2014) investigated the reliability of a 5 repetition
maximum. They had 25 subjects 16 men and 9 women who performed 5RM leg press and
5RM leg curl. The results of this study showed that all ICC with 5RM testing were above a
95% with low CV. The finding of this study showed that 5-RM strength test is a reliable and
simple measurement method in healthy men and women and can be used by athletic
coaches, health and fitness professionals as well as rehabilitation specialist. Used to quantify
the level of muscle strength, to assess muscle strength imbalances, to evaluate strength
training programs and to prescribe load for strength training. Compared to the 1RM strength
test, the advantage of the 5-RM test is a potentially lower risk of muscle injury in the test
phase and there is no need for a laborious preparation of the participants (Gail &
Kunzell,2014).
Mechanisms of Relative Strength
The mechanisms of relative strength consist of three phases (Suchomel et.al., 2016).
The literature indicates that central and local factors enhance the ability to increase maximal
strength through motor unit recruitment, fiber type, and co-contraction with in the
musculature of the athlete (Wetmore et.al., 2020; Zamparo et.al., 2002). The three phases of
the mechanisms of relative strength are the strength deficit phase, strength association phase,
and strength reserve phase. The three different phases of mechanism of relative strength are
16
vital to understanding the relationship between relative strength and joint mobility because
understanding one’s relative strength could be predictive of joint mobility (Suchomel et.al.,
2016).
The strength deficit phase which is the shortest phase based on the motor learning
capacity of the individual (Suchomel et.al., 2016). During this phase, the individual
improves their strength and ability to produce force. He/she may not have the ability to
exploit their levels of strength and translate them into performance benefits in their
respective sports. The novice athletes in this phase are often going through physical literacy
not being exposed to strength training before. This phase continues until the athlete is
competent with training (Bayli, 2004; Ford et.al., 2011). Within firefighters it is shown that
a majority fall within the strength deficit phase. Based upon Exercise Simulated Fire Ground
Test (EX-SFGT), the National Fire Protection Association states that 70% of active duty
firefighters are to be considered untrained (Dennison et.al., 2012). Firefighting is a strenuous
occupation that requires optimal levels of physical fitness and transition from the strength
deficit phase through increases in relative strength may indicate higher scores on the EX-
SFGT.
The strength association phase occurs as individuals get stronger. Where this
increase in strength often directly translate to an improved performance. This happens
because of further increases in absolute strength combined with coordination and central
factors enhancing the athlete’s ability to increase muscular performance. This performance
increase is caused primarily by two physiological mechanisms including muscle cross-
sectional area or architectural changes and supraspinal/ spinal neuromuscular adaptations
17
that occur as a result of regular strength training (Suchomel et.al., 2016). Specifically, the
cross-sectional area or architectural changes that are characteristic of strength training are
greater Type II/I functional cross-sectional area and pennation angle changes (Campos et.al.,
2002; Häkkinen & Keskinen, 1989; Häkkinen et.al., 1981; Kawakami & Fukunaga, 1993).
Studies that have examined training for strength have reported muscle architecture changes
after 4-5 weeks and increase tendon stiffness after 9-10 weeks (Kubo et.al., 2010; Seynnes
et.al.,.2009). These changes may affect the electromechanical delay and rate of force
development during stretch-shortening cycle tasks. This is important for the time needed for
positive training adaptations to occur (Bojsen-Møller et.al., 2005; Kubo et.al., 2010;
Seynnes et.a., 2009; Reuer, 2017). Mayer & Nuzzo, (2015) investigated the effects of 24
weeks of training on muscle hypertrophy of the lumbar multifidus muscles in healthy
fireman. The cross sectional area of the lumbar multifidus muscles in firefighters was
assessed using an ultrasonography. The data from this study was used to identify the impact
of supervised worksite exercise programs by Mayer et.al., (2015). The results that
firefighter’s lumbar multifidus musculature was larger than general populations following
training. The findings of these studies indicated that a supervised worksite exercise program
for firefighters was a safe and effective way to improve back musculature (Mayer et.al.,
2015). Firefighter strength training exercise may lead to hypertrophy improving strength and
leading to strength improvements in the strength association phase.
The strength reserve phase is the final phase of the model. Athletes who reach this
phase have dramatically improved their ability to produce force primarily due to local and
central adaptations and alterations in task specificity (Kraemer & Newton, 2000; Stone
et.al., 2002). During the strength reserve phase, athletes may continue to gain relative
18
strength; however, the direct benefits to performance may not be as substantial. Kraemer and
Newton (2000) suggest while strength is a basic quality that influences an athlete’s
performance, the degree of this influence may diminish when athletes maintain a very high
level of strength. It should be note, however that individuals should not seek to continue
improving their strength, rather stronger individuals can focus more on maintaining their
strength, while placing more emphasis on RFD and speed adaptations. The differences in
performance between individuals that can squat greater than or equal to 2.59 x their body
mass, versus 2.09 x their body mass and 1.59 x their body mass. No research has discussed
the changes in performance after transitioning from a 2.09 to a 2.59 body mass squat
(Bojsen-Møller et.al., 2005; Campos et.al., 2002; Häkkinen & Keskinen, 1989; Häkkinen
et.al., 1981; Kawakami & Fukunaga, 1993; Kraemer & Newton 2000; Kubo et.al., 2010;
Seynnes et.al.,2009). Attaining a enhanced level of relative strength will lead to a plateau in
strength increases which has not been fully investigated. This shows that the current
literature cannot identify all aspects related to relative strength and its mechanisms.
Finally, the three phases of the mechanisms of relative strength the strength deficit
phase, strength association phase, and strength reserve phase can and should be used in
training regimes for firefighters to ensure adequate progression to improve their
performance ability on duty. The three different phases of mechanism of relative strength
are vital to understanding the relationship between relative strength and joint mobility in
firefighters because understanding one’s relative strength could be predictive of joint
mobility (Suchomel et.al., 2016).
19
Joint Mobility and Association with Strength
Flexibility is defined as the ability of a muscle or muscle groups to
lengthen passively through a range of motion (Haff & Triplett, 2016). Whereas mobility is
the ability of a joint to move actively through a range of motion (Haff & Triplett, 2016).
Many additional factors define the capabilities of a person’s mobility. One additional factor
is the muscle stretching over a joint but also how far the joint moves within the joint
capsule. Another factor is the component of motor control within the nervous system (Haff
& Triplett, 2016; Median McKeon & Hoch, 2019; Park et al.,2015).
Joint mobility is a direct determinant of posture and movements, influencing activity
and participation for all individuals. The relationships between joint mobility and strength
has been reported in the literature. Riganas et al., (2010) reviewed isokinetic strength and
joint mobility by investigating oarside and nonoarside lower extremity asymmetries in
isokinetic strength and joint mobility of port and starboard oarsmen. Results showed torques
of right and left extensors and flexors were measured on isokinetic dynamometer at angular
velocities of 60 and 180°·s-1 in 12 starboard (n = 12; training age 5.55 ± 0.52 years) and 14
port (n = 14; training age 6.09 ± 0.95 years) well-trained male rowers (Riganas et.al., 2010).
They assessed mobility of the hip, knee, and ankle joints using a Myrin flexometer, a
modification of the Leighton flexometer. The findings of this study indicated that ports had a
significantly higher peak torque in oarside right knee extensors at 60°·s-1 (p < 0.001) and
180°·s-1 (p < 0.01) compared to in the nonoarside left knee extensors (Riganas et.al., 2010).
They also found that starboards had a higher peak torque in left knee extensors at 60°·s-1 (p
< 0.05) and 180°·s-1 (p < 0.05) compared to the right side. Right flexors peak torque was
20
significantly higher in ports compared to that in starboards at 60°·s-1 (p < 0.05) and 180°·s-
1 (p < 0.01). The researchers found no significant difference between port and starboards in
left knee flexors at either angular velocity. Both port and starboards showed higher hip (p <
0.01) mobility in oarside compared to in nonoarside. Riganas et.al., (2010) concluded that
sweep rowers develop a significantly higher knee flexion peak torque and hip mobility. A
correlation between isokinetic strength and joint mobility demonstrating a link between
mobility and strength gives insight to further research the relationship between these two
variables. Strengthening and mobility training programs to compensate for potential
imbalances may reduce the occurrence of injuries. Sokoloski et.al., (2020) investigated the
effects of a 6 month, 2 sessions a week training program on fitness parameters in
firefighters. The findings of this study indicated that mobility improvements were achieved
that may be due to the flexibility and anaerobic fitness training that these firefighters
underwent (Sokoloski et.al., 2020).
Functional Movement Screen
The Functional Movement Screen is used to assess and evaluate fundamental
patterns of movement. The Functional Movement Screen (FMS) is a movement screening
tool designed to assess movement quality and asymmetries in movement with the potential
to identify injury risk. This proven assessment allows individuals and instructors to identify
asymmetries and dysfunctions in seven different movements. Research proves these factors
will increase the risk of injury (Minthorn et.al., 2015). Firefighters require a high level of
functional fitness to operate safely, effectively, and efficiently. A study in 524 firefighters
who completed the Functional Movement Screening (FMS) identified that those who
21
obtained a score of 14 or less as a sign of movement dysfunction and mobility impairments
with higher injury rates (Jafari et.al., 2020). The FMS scores of 43% of the firefighters who
participated in the study scored less than 14 indicating that they display signs of movement
dysfunction and mobility impairments (Jafari et.al., 2020). This study and others have
shown that FMS scores less than 14 increase the injury risk (Bonazza et.al., 2017; De
Oliveira et.al., 2017; Jafari et.al., 2020; Hoover et.al., 2020; Marques et.al., 2017; Moran
et.al., 2017; Shore et.al., 2020; Smith et.al., 2017; Trinidad-Fernandez et.al., 2019). These
studies showed low FMS scores could be improved to 14 and higher through training
protocols. Considering the high injury rate of firefighters, administering FMS periodically
and to use a training protocol developed to improve FMS scores to increase function and
mobility may help to increase functional fitness and reduce injury risk (Jafari et.al.,.2020;
Minthorn et.al., 2015; Stanek et.al., 2017). Stanek et.al., (2017) examined fifty-six male
firefighters who all volunteered as the subjects tested the scores of the Functional Movement
Screening in active duty firefighters showing that increased FMS scores showed lower rate
of injuries while on duty. Firefighting is a dangerous occupation that requires adequate
functional movement patterns. Developing training programs with the objective of
increasing FMS scores may contribute to reducing the risk of injury on the job.
This can be used for tactical athletes such as firefighters but can also be implemented
into other tactical populations such as the United States Military. The United States Army
Rangers are a unique population whose training requirements are intensive, and physically
and mentally demanding. Davis et.al., (2020) investigated associations between FMS scores
and the various measures of health and performance of active duty soldiers in light infantry
units who were involved in the U.S. Army Pre-Ranger Course (PRC). A total of 491 male
22
soldiers with the average age of them being 24 3.8 years. The soldiers completed the FMS
and the FMS results were used to make a determination of asymmetries (i.e., differences in
FMS scores between the right and left side of the body) and mobility impairments were
made. The soldiers also completed the Army Physical Test (APFT) as data to compare to the
FMS. The average composite FMS score was 16.4 ±1.9 points demonstrating that active
duty soldiers of a light infantry division achieved FMS scores similar to other military
populations tested, and the composite FMS score was related to higher APFT scores and
absence of previous musculoskeletal injuries (Davis et.al., 2020). Higher FMS score was in
populations with tactical athletes such as firefighters and soldiers demonstrated a direct
correlation with decreased risk of injury while on duty.
Firefighters Needs Analysis
Firefighters work in unpredictable, every-changing conditions. The ability for a
firefighter to adapt and overcome is a necessity when on the job. Firefighters are at risk of
injury and the use of personal protective equipment (PPE) is a necessity while on duty.
However, the additional weight from the PPE and self-contained breathing apparatus
(SCBA) alters their center of mass (COM), restricts movement and limits vision (face mask)
contributing to the challenge of functional ability on duty (Brown et.al., 2019).
Firefighters put themselves at risk by choice. Firefighting is a high risk profession,
approximately 80,000 firefighters are injured and 100 firefighters die on the job each year in
the United States (Kahn et.al., 2017; Smith, 2011). Kahn et.al., (2017) investigated variables
that put firefighters at risk for potentially preventable workplace mortality such as use of
personal protective equipment (PPE), seat belts, and appropriate training, fitness, and
23
clearance for duty. Results of this investigation showed that firefighters who worked in
departments that lacked standard annual fitness testing were statically implicated a fatality
risk (Kahn et.al., 2017). This study showed that fitness is a factor contributing to the health
and safety of the firefighter while on duty.
A limited amount of studies in the current literature have examined the relationship
between relative strength and mobility in firefighters. Some research discusses absolute
strength in this population but did not examine relative strength (Perroni et al., 2015; Sheaff
et al., 2010). Firefighter’s relative strength is important because the weight of their Personal
Protection Equipment (PPE) typically weighs 45 pounds or more (Lackore, 2007).
Additionally, firefighters may also carry loads exceeding 72 total extra pounds they have to
carry (Lackore, 2007). The equipment that can represent as much as 20%-40% of their body
weight when responding to fire calls (Lackore, 2007).
Relative strength is a necessity for a firefighter to be able to perform at their
occupation. Relative strength has been demonstrated to increase athletic performance and
with firefighters being tactical athletes who have to carry loads far greater than their
respective body weight, increased relative strength may increase the occupational ability of
firefighters. The ability to manage one’s body weight and the weight of their equipment is
vital for success and survival while on duty because the increased load carriage places a
higher physical demand on the firefighter (Lesniak et. al., 2020). Enhanced ability to carry
loads while on duty will help to increase occupational performance. Lesniak et.al., (2020)
investigated the effects load carriage has on firefighter’s work capacity to enhance the
understanding of occupational demand. Occupational performance was assessed in twenty-
one male firefighters were the subjects of this study where they assessed occupational
24
performance by time to complete a simulated fire ground test. Results of this showing that
PPE significantly decreases the work capacity and increases the perceived effort of
occupational tasks. The findings describe the additional physical demands produced by PPE
and indicate that performance of firefighting tasks in an unloaded condition does not reflect
work capacity in a real firefighting condition (Lesniak et. al, 2020).
A key study performed by Coca et al., (2015) demonstrated the restrictions placed
upon of movement from the firefighting equipment and gear. The aim of the study was to
determine the effects of firefighter’s protective ensembles on mobility and performance by
measuring static ranges of motion and job related tasks (Coca et.al., 2015). The study used
firefighters between the ages of 20-40 years. The range of motion doing specific tasks while
wearing standard PPE and regular light clothing was assessed. The use of PPE resulted in a
decreased range of motion in shoulder flexion, cervical rotation and flexion, trunk lateral
flexion, and stand and reach (Coca et.al., 2015). The results indicated the PPE that
firefighters decreased ranges of motion is shoulder flexion, cervical rotation and flexion,
trunk lateral flexion, and stand and reach (Coca et.al., 2015). The range of motion
preforming one arm search task and object was significantly decrease with the use of PPE
(Coca et.al., 2015). The overall finding of this study support the need for ergonomic
evaluation of protective clothing systems to help improve human movement patterns in this
gear.
PPE is an essential part of firefighting and the effects that it has on firefighter’s
mobility is more than just physical. Wang et. al., (2021) investigated the effects of PPE on
firefighters' perceptions of mobility and their experienced occupational injury risks between
China and the USA. This consisted of online survey with a total of 328 firefighters,
25
including 203 Chinese firefighters and 125 United States firefighters. Both Chinese and US
firefighters ranked mobility restriction as the most dissatisfactory characteristic of the
current their PPE. Restricted mobility while wearing PPE was closely related to the risk for
musculoskeletal disorders (Wang et. al., 2021). The findings suggested that PPE design
should consider a balance in the weight distribution of SCBA and the overall interface of
turnout gear and equipment, flexibility of materials for boots should be emphasized to
increase mobility and reduce the risks of musculoskeletal disorders.
The relationship between relative strength and mobility in the population of
firefighters may provide the insight to improve performance, prevent injuries and fatalities.
Providing firefighters and fire departments the information needed to refine training enhance
occupational duties to creates safer communities for everyone (Smith, 2011; Windisch,
2017). The proper use of the phases of relative strength and its association with joint
mobility in firefighters can be a vital key to understanding the relationship between relative
strength and joint mobility in firefighters to improve occupational performance due to the
limiting factors of their PPE.
Literature Review Conclusions
To conclude, the four forms in which to express strength. Four forms of strength:
absolute strength, strength endurance, power or explosive strength and relative strength have
been studied and validated in the literature (Dirnberger et.al., 2012; Sökmen et.al., 2018).
Relative strength is a topic in the literature that has been researched but not as extensively as
other forms of strength. Relative strength is the amount of strength compared to the size of
the individual’s bodyweight (force per unit of body weight) (Clemons, 2014). This
26
represents an individual’s ability to move their body through space (Ronai & Scibek, 2014).
Relative strength being a predictor of injury it can also be a predictor of athletic performance
(Andersen et. al., 2018; Case et.al., 2020; Nuzzo et.al., 2008; Wilsoff et.al., 2004). Adequate
relative strength is important to successful athletic performance as well as performance of
activities of daily life (Baechle & Earle, 2008). Relative strength and peak force production
show a linear relationship (Aagaard et.al., 2002).
The literature shows the mechanisms of relative strength consist of three phases
(Suchomel et.al., 2016). This phase progression concept is shown and supported by the
literature. The literature indicates that central and local factors enhance the ability to
increase maximal strength through motor unit recruitment, fiber type, and co-contraction
with in the musculature of the athlete (Wetmore et.al., 2020; Zamparo et.al., 2002).
The relationships between joint mobility and strength has been reported in the
literature. Joint mobility is a direct determinant of posture and movements, influencing
activity and participation for all individuals (Park et al.,2015; Median McKeon & Hoch,
2019; Haff & Triplett, 2016). Mobility is the ability of a joint to move actively through a
range of motion (Median McKeon & Hoch, 2019; Haff & Triplett, 2016).
Firefighter’s daily tasks require superior relative strength having to perform duties
such as running upstairs, climbing ladders, ceiling breach and pull, carrying equipment,
forcible entry, dragging hoses, raising ladders and extension, and rescue of patrons in heavy
protective equipment that limits their range of motion (Coca et al., 2015; Peterson et
al.,2008; Park et al., 2015; Orr et al., 2019). Approximately 80,000 firefighters are injured
and 100 firefighters die on the job each year in the United States because of the lack of
fitness programs for fire departments (Kahn et.al., 2017; Smith, 2011). Firefighter’s number
27
on concern about their PPE is how it affects their mobility while performing occupational
duties (Wang et. al., 2021). This is more than just a concern, the literature has shown that
range of motion was significantly decreased with the use of PPE (Coca et.al., 2015).
Firefighter’s physical demands are increased while wearing PPE and indicate that
performance of firefighting tasks in an unloaded condition does not reflect work capacity in
a real firefighting condition (Lesniak et. al., 2020). Firefighters need an increased carry
capacity to be able to meet the demands that their PPE puts on them (Lesniak et. al., 2020).
All of these topics have been covered extensively in the previous literature. The
current literature is lacking the investigation of relative strength and joint mobility in
firefighters and there is need for examination of this relationship to occur. This examination
is required because of the factors that firefighter’s PPE induces on them while on duty. PPE
placing loads on firefighters that requires superior relative strength and PPE that is highly
restrictive of joint mobility requires enhance joint mobility to ensure safety and occupational
success when on duty.
28
CHAPTER III
METHODOLOGY
The purpose of this investigation was to identify the relationship between relative
muscular strength in selected upper and lower body movements and joint mobility in
corresponding joint systems in firefighters.
Participants
Following approval from the Institutional Review Board at Eastern Illinois
University, a volunteer sample was recruited from the Charleston, IL Fire Department. The
department personnel available to participate in this study consisted of: 24-Firefighters, 6-
Lieutenants, 3-Captains, 1-Chief, 1-Asssitsant Chief, for a total of 35 potential subjects.
Potential subjects were required to be between the ages of 18-57 years to participate. The
upper age limit was set because the U.S. Department of Interior Information on Special
Retirement for Firefighters mandate a retirement age of 57 years upon reaching 20 years of
service (Walker, 2003). All participants provided their voluntary, informed consent
(Appendix A) and completed health history questionnaire with the following exclusion
criteria: no reported acute musculo-skeletal injury or limitations in mobility secondary to
past injury, surgery or abnormalities, arthritis, malignant diseases, unstable cardiac
conditions or neurological problems (Appendix B).
Recruitment Procedures
Prior to making contact with the fire department staff for the purpose of recruitment,
the proposed study was presented to the Charleston Fire Department’s Chief for approval
and permission to recruit members of the department and to do so during work hours. After
29
permission was granted, flyers (Appendix C) explaining the objective, requirements and
procedures of the study were distributed to the Firefighters and a 5-minute oral presentation
was given to each of the three shifts.
Equipment
The following equipment was utilized to perform the assessments needed for this
study:
Leighton Flexometer (# 505173)
Standard American Olympic Barbell (Ivanko Barbell 1967, OB-20 USA Olympic
Bar, 28.5 mm diameter, 45lbs, Los Angeles, CA)
Olympic Barbell Plates in pounds (Ivanko Barbell 1967, OBP-TRAINING, 50mm
diameter, Los Angeles, CA) all weighed for statistical accuracy.
Squat Rack (Hammer Strength HDT-HR, Cincinnati, OH)
Lifting Bench (Hammer Strength FW-FB, Cincinnati, OH)
Pull Up Bar (Hammer Strength HDT-HR, Cincinnati, OH)
Weight Scale (Model# HDL545DQ-63 B197DT, Healthometer, 2009 Sunbeam
Products, Boca Raton, FL)
Leighton Flexometer
The Leighton Flexometer is a gravity dependent goniometer consisting of a 360-
degree dial and weighted gravity needle and a strap which attaches the device to a limb. The
aim of this assessment is to measure the degrees of range of motion in a joint, which is
important for injury prevention and execution of many sporting movements and everyday
life tasks. The Flexometer is strapped to the body segment that is mobile with a given joint
30
action. The dial is locked at 0 degrees at one extreme of the range of movement. After the
body segment has moved to the new position, the needle is locked at the other extreme of
the range of motion. The maximal degree of arc through which the movement takes place is
read directly from the dial.
Procedures
Data collection took place at a private fitness center owned by a member of the local
fire department. Subjects were scheduled for testing individually at their convenience. Data
collection was performed in relative privacy away from the general clientele using the
facility.
COVID Safety Guidelines
The Eastern Illinois University Institutional Review Board (IRB) updated Human
Subject Research published on 8/13/2020 re-authorized research protocols that require
person to person interaction as long as they follow the most current guidelines set forth by
the Center for Disease Control (CDC and follow local and state recommendations). The
CDC recommendations for preventing COVID-19 are “that hands are sanitized using at least
60% alcohol sanitizer, practice social distancing from others, especially for people who are
at higher risk, properly wearing a mask in a public setting, maintaining social distancing of
six feet or greater, and clean and disinfect frequently touched surfaces daily” (CDC, 2020).
These guidelines were adhered to in all interactions with participants.
The participant’s body weight in pounds was measured to the nearest (0.1) pound
without shoes and in minimal clothing before mobility and strength testing was assessed.
Mobility was assessed using a Leighton Flexometer to measure joint ROM in different
31
active movement patterns (Leighton, 1966). Mobility was assessed before the strength
testing was performed. Ranges of motion for each joint/movement were assessed one time.
All assessments of mobility were conducted on the right side of the body for standardization
of the data. Mobility was assessed in the lower body movements by tibiofemoral joint ROM
with flexion for the knee complex with standing knee flexion (McCarthy et. al, 2013). The
talocrucal joint ROM for the ankle complex with active Plantar Flexion and active Dorsi
Flexion was executed (Schoenfield, 2010). Additionally, acetabulofemoral joint mobility
was assessed by the ROM in the acetabulofemoral joint during an active straight leg flexion.
For upper body mobility ROM was assessed via active standing shoulder flexion without
shoulder girdle engagement (Schory et. al, 2016; Kong, 2016; Wattanaprakornkul et. al,
2011). Active flexion of the humeroulnar joint was also assessed for upper body mobility
(Ludewig et al.,2009).
Strength was tested using a sub-maximal 5-repetition protocol to estimate maximum
strength rather than a 1RM for subject safety as not all participants had experience with
weight lifting (Dohoney et al.,2002; Jidovtseff et al.,2011). The testing protocol for each
strength test consisted of an equipment familiarization set of 10 repetitions with less than
50% of the of participant’s perceived maximum, 10 repetitions of 50% of the estimated 5
RM, 5 repetitions at 75% of estimated 5 repetition maximum, 3 repetitions at 90% of
estimated 5RM, and a 5 repetition maximum set (Reynolds et al., 2006; Tan et al., 2015;
Macht et al., 2016; Beckham et al.,2018). The following equation was used to estimate the
subjects 1 RM (Haff & Triplett, 2016; Shephard, 2009; Baechle & Earle, 2008):
Estimated 1RM= 5RM weight (lbs) 0.87 EQ. 1
Where:5RM=the weight lifted 5 times only
32
Using the participant’s bodyweight, a ratio of relative strength was calculated for each of the
movement patterns (Dohoney et al.,2002; Haff & Triplett, 2016; Shephard, 2009; Baechle &
Earle, 2008):
Relative strength = Estimated 1RM (lbs) Body weight (lbs) EQ. 2
Strength was assessed using the back squat as a lower body push, a conventional
deadlift as a lower body pull, and bench press as an upper body press. These barbell
movements were selected because of previous literature establishing their validity for
quantifying strength (Ferland et al.,2020). The fourth movement is a weighted, strict,
pronated pull up which is an upper body pull. A weight belt was used to add weight to this
movement to illicit a 5RM if the firefighter was capable of performing more than 5 body
weight repetitions. This was determined during the warm up prior to attempting the
movement (Ronai & Scibek, 2014).
After data was collected, upper body mobility total and lower body mobility total
scores were calculated. Upper body mobility scores were calculated by the addition of the
degrees of ROM in shoulder extension and elbow extension (Khalil et.al., 2021). Lower
body mobility total was calculated by the addition of the degrees of ROM in dorsi flexion,
plantar flexion, knee flexion, and hip flexion (Hyodo et.al., 2017). Super total was also
calculated which was the addition of predicted 1RM’s of the pronated pull up, bench press,
back squat and conventional deadlift (Ferland & Comtois ,2019; Robisnson et.al., 2018).
Analysis
Data analysis included the calculation of descriptive statistics (Mean ± Std. Dev) for
all dependent variables from the assessments of mobility, strength testing, and Health
33
History Questionnaire (Appendix B). A Pearson Product-Moment correlation (r) and
associated significance levels (p) (MS Excel) was performed to examine the relationship
between measures of mobility and strength. A Pearson Product-Moment correlation (r) was
performed to examine the relationship between the full body relative strength ratio and
training status. An alpha of ≤ .05 was established as the determination of significance.
34
CHAPTER IV
RESULTS
The purpose of this investigation was to identify the relationship between relative
muscular strength and joint mobility in firefighters. It was hypothesized that those
firefighters with increased mobility would have a greater relative strength; conversely, the
firefighters who had decreased mobility would also have lower relative strength. This study
examined strength by testing firefighters during the back squat as a lower body push, a
conventional deadlift as a lower body pull, and bench press as an upper body press
exercises. Mobility was assessed using a Leighton Flexometer to measure joint range of
motion ROM.
Subjects
Twelve Firefighters volunteered and participated in the study. Eleven out of the
twelve firefighters completed all portions of the study. The twelve male firefighter
volunteers ranged in age from 25-52 years (37.7 7.7), (Table 1). The participant’s body
weight ranged 269.5-161.26 pounds (202.36 31.99), (Table 1 & Figure 1). One of the
firefighters was unable to do the lower body strength testing portion of the study due to
contraindications related to having a history of an Anterior Cruciate Ligament (ACL)
Reconstruction and Meniscus repair on his left knee within a year of the study. This
firefighter did complete the upper body strength testing protocols.
35
Health History Questionnaire
Three of the subjects of the study listed in Health History Questionnaire (Appendix
B) that they were diagnosed with SARS-CoV-2 virus (COVID-19) during the year of 2020.
Five of the subjects of the study stated in their Health History Questionnaire section on
health habits and personal safety section (Appendix B) that they were on a specific diet. Two
of the subjects stated that they were on a weight loss diet using the method of a caloric
deficit diet with normal ratios of macronutrient intake. Two of the subjects stated that they
were dieting to increase muscle mass by having a higher protein intake and being in a
caloric surplus. One of the subjects stated that they are performing and Intermittent Fasting
(IF) diet. The subjects of this study also recorded their caffeine intake in the health habits
and personal safety section of the Health History Questionnaire (Appendix B). All subjects
of this study indicated the use of the drug caffeine by means of ingesting coffee, soda, tea,
energy drinks, and/or pre workout supplements. Caffeine intake of the subjects ranged from
80-800 mg per day (247.5 188.6), (Table 1). The subjects recorded their current exercise
training status in the health habits and personal safety section of the Health History
Questionnaire (Appendix B). In this section there were four choices, Sedentary (No
exercise), Mild exercise (i.e., climb stairs, walk 3 blocks, golf), Occasional vigorous
exercise (i.e., work or recreation, less than 4x/week for 30 min), Regular vigorous exercise
(i.e., work or recreation 4x/week for 30 minutes). These were rated on a scale of 1-4 scale
where 1 was sedentary and 4 being regular vigorous exercise. The results of the self-reported
training status of current exercise ranged from 2-4 (3.42 .9), (Table 1).
36
Table 1
Descriptive Statistics for Subject Characteristics from the Health History Questionnaire
(HHQ)
Variable Mean (SD)
Age (Years) 37.7 (7.7)
Weight (lbs) 202.36 (31.99)
Caffeine Intake (Milligrams) 247.5 (188.6)
Training Status (1-4) 3.42 ( .9)
37
Figure 1
Distribution of Participant’s Body Weight Immediately Prior to Study
269.5
173.36
188.6
205
175
213204.75
180184.8
161.26
233.86239.14
0
50
100
150
200
250
300
1 2 3 4 5 6 7 8 9 10 11 12
Po
un
ds
(lb
s)
Partcipants
38
Joint Mobility
Mobility was assessed using a Leighton Flexometer to measure joint range of motion
(ROM) in different active movement patterns: Dorsi Flexion, Plantar Flexion, Knee flexion,
Hip Flexion, Shoulder Flexion, and Elbow Flexion (Leighton, 1966). Mean results for the
measures of ROM are shown in Table 2.
Table 2
Joint Mobility ROM Means and Standard Deviations in Firefighters
Joint Action Range of Motion (Degrees)
Mean (SD)
Dorsi Flexion 14.34 (5.38)
Plantar Flexion 14.67 (6.15)
Knee Flexion 103.08 (19.93)
Hip Flexion 97.16 (17.06)
Shoulder Flexion 98.75(14.69)
Elbow Flexion 115.34 (21.91)
The distribution of individual values for ROM are shown in the following figures:
Dorsi Flexion, Figure 2; Plantar Flexion, Figure 3; Knee Flexion, Figure 4; Hip Flexion,
Figure 5; Shoulder Flexion, Figure 6; Elbow Flexion Figure 7.
Upper and lower body mobility totals were also calculated. The lower body mobility
total consisted of the addition the dorsi flexion score, plantar flexion score, knee flexion
39
score, and hip flexion score. The lower body mobility total was an average of 229.25
33.94 degrees see Figure 8. The upper body mobility total consisted of the addition of the
shoulder flexion without shoulder girdle engagement score and elbow flexion score. The
upper body mobility total was an average of 214.08 30.63 degrees, Figure 9.
40
Figure 2
Dorsi Flexion Range of Motion in Degrees ROM
19
12
14
21
24
6
12
14
12
11
19
8
0
5
10
15
20
25
30
1 2 3 4 5 6 7 8 9 10 11 12
Deg
rees
of
RO
M
Partcipants
41
Figure 3
Plantar Flexion Range of Motion in Degrees ROM
17
4
19
10
8
13
22
8
15
24
17
19
0
5
10
15
20
25
30
1 2 3 4 5 6 7 8 9 10 11 12
Deg
rees
of
RO
M
Partcipants
42
Figure 4
Standing Active Knee Flexion range of Motion in Degrees ROM
65
105
90
130
114
119117
84
119
105
113
76
0
20
40
60
80
100
120
140
1 2 3 4 5 6 7 8 9 10 11 12
Deg
rees
of
RO
M
Partcipants
43
Figure 5
Active Straight Leg Raise Range of Motion in Degrees ROM
51
102
95 94
103
116114
9997
106 106
83
0
20
40
60
80
100
120
140
1 2 3 4 5 6 7 8 9 10 11 12
Deg
rees
of
RO
M
Partcipants
44
Figure 6
Shoulder Flexion without Shoulder Griddle Engagement Range of Motion in
Degrees ROM
92
114
120
96
116
99
85
9296
67
108
100
0
20
40
60
80
100
120
140
1 2 3 4 5 6 7 8 9 10 11 12
Deg
rees
of
RO
M
Partcipants
45
Figure 7
Elbow Flexion Range of Motion in Degrees ROM
124
107
167
136
104
110
103
94
137
96 95
111
0
20
40
60
80
100
120
140
160
180
1 2 3 4 5 6 7 8 9 10 11 12
Deg
rees
of
RO
M
Partcipants
46
Figure 8
Sum of All Lower Body Mobility Values in Degrees ROM
152
223218
255249
254
265
205
243 246
255
186
0
50
100
150
200
250
300
1 2 3 4 5 6 7 8 9 10 11 12
Deg
rees
of
RO
M
Partcipants
47
Figure 9
Sum of All Upper Body Mobility Values in Degrees ROM
216221
287
232
220
209
188 186
233
163
203211
0
50
100
150
200
250
300
350
1 2 3 4 5 6 7 8 9 10 11 12
Deg
rees
of
RO
M
Partcipants
48
Firefighters Absolute Strength Results
Eleven out of the twelve firefighters completed all upper and lower body strength
tests. One subject was unable to complete the lower body tests due to previous knee surgery.
The mean results for estimated 1RM strength for the four exercise performed and the super
total are shown in Table 3. The super total The super total result excludes the firefighter who
only completed the upper body strength testing.
Table 3
Estimated 1 Repetition Maximums Means and Standard Deviations in Firefighters (n=11)
Exercise Mean (SD)
Bench Press (lbs) 238.78 (57.33)
Back Squat (lbs) 282.67 ( 65.49)
Conventional Deadlift (lbs) 327.15 (59.02)
Pronated Pull Up (lbs) 230.58 (28.39)
Super Total (lbs) 877.11 (197.69)
The distribution of individual values for absolute strength are shown in the following
figures: Estimated Bench Press One Repetition Maximum (lbs), Figure 10; Predicted Back
Squat One Repetition Maximum (lbs), Figure 11; Predicted Conventional Dead Lift One
Repetition Maximum (lbs), Figure 12; Predicted Pronated Pull Up One Repetition
Maximum, Figure 13; Super Total Maximum (lbs), Figure 14.
49
Figure 10
Distribution of Estimated Bench Press 1RM Among Firefighters
263.2
305.6311.7
271.1
242
258.6
281.3
118.3
199
172.4
247.4
194.8
0
50
100
150
200
250
300
350
1 2 3 4 5 6 7 8 9 10 11 12
Po
un
ds
(lb
s)
Partcipants
50
Figure 11
Distribution of Estimated Back Squat 1RM Among Firefighters
338.7331.3
250
300
353
242
310.5
240
258.6
135.3
350
0
50
100
150
200
250
300
350
400
1 2 3 4 5 6 7 8 9 10 11
Po
un
ds
(lb
s)
Partcipants
51
Figure 12
Distribution of Estimated Conventional Dead Lift 1RM Among Firefighters
373.6
394.5
318.2
419.5
357.9
310.5 305.6
247
264.7
247
360.2
0
50
100
150
200
250
300
350
400
450
1 2 3 4 5 6 7 8 9 10 11
Po
un
ds
(lb
s)
Partcipants
52
Figure 13
Distribution of Estimated Pronated Pull Up 1RM Among Firefighters
269.5
239 237.3
256.3
229.9
250.2
241
180
217.4
173.4
233.86239.14
0
50
100
150
200
250
300
1 2 3 4 5 6 7 8 9 10 11 12
Po
un
ds
(lb
s)
Partcipants
53
Figure 14
Sum of the 4 1RMs (Super Total)
1245
1031.4
879.9
990.6952.9
811.1
897.4
605.3
722.3
554.7
957.6
433.94
0
200
400
600
800
1000
1200
1400
1 2 3 4 5 6 7 8 9 10 11 12
Po
un
ds
(lb
s)
Partcipants
54
Firefighters Relative Strength Results
The relative strength ratio for the 12 firefighters (n=11 for lower body lifts) for each
of the exercise movements were calculated. The mean relative strength ratio for each of the
four exercises performed are shown in Table 4.
Table 4
Relative Strength Ratios Means and Standard Deviations Among Firefighters
Exercise Ratio Mean (SD)
Bench Press 1.19 (.32)
Pronated Pull Up 1.15 (.13)
Back Squat 1.42 (.32)
Conventional Deadlift 1.66 (.31)
55
Figure 15
Distribution of Individual of Bench Press Relative Strength Ratio Scores
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
1 2 3 4 5 6 7 8 9 10 11 12
1R
M/l
bs
bo
dy
wei
ght
Partcipants
56
Figure 16
Distribution of Individual of Back Squat Relative Strength Ratio Scores
0
0.5
1
1.5
2
2.5
1 2 3 4 5 6 7 8 9 10 11
1R
M/l
bs
bo
dy
wei
ght
Partcipants
57
Figure 17
Distribution of Individual of Conventional Deadlift Relative Strength Ratio Scores
0
0.5
1
1.5
2
2.5
1 2 3 4 5 6 7 8 9 10 11
1R
M/l
bs
bo
dy
wei
ght
Partcipants
58
Figure 18
Distribution of Individual of Pronated Pull Up Relative Strength Ratio Scores
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1 2 3 4 5 6 7 8 9 10 11 12
1R
M/l
bs
bo
dy
wei
ght
Partcipants
59
Figure 19
Super Total Relative Strength Ratio
0
1
2
3
4
5
6
7
1 2 3 4 5 6 7 8 9 10 11
1R
M/l
bs
bo
dy
wei
ght
Partcipants
60
Absolute Strength
Using the data collection from all twelve firefighters, correlation was calculated
comparing all absolute strength values of 1RM in the bench press, back squat, conventional
deadlift, and pull with each of the mobility values of ROM in dorsi flexion, plantar flexion,
standing knee flexion, hip flexion, shoulder flexion without shoulder girdle engagement, and
elbow flexion. Only the data of the eleven firefighters who complete the tests of lower body
strength was used for lower body strength correlations. Correlation coefficients between
measures of strength with mobility are shown in Table 4. There were moderate, significant
correlations observed between absolute strength in the back squat and ROM in ankle dorsi
flexion r(9)=.62, p=.041, (Table 4, Figure 20; absolute strength in the conventional dead lift
and ROM in dorsi flexion r(9)=.58,p=.048, (Table 4, Figure 21) and between absolute
strength in the back squat and ROM in shoulder flexion r(9)=.60,p=.039 (Table 4, Figure
22).
61
Table 4
Correlations for Absolute Strength 1RM and Degrees ROM in Firefighters(r=.61)
Bench Press Back Squat
Conventional
Dead Lift
Pull Up
Dorsi Flexion
.17
.62*
.58*
.19
Plantar Flexion
-.06
-.42
-.42
-.10
Knee Flexion
.23
.01
.13
.005
Hip Flexion
-.005 -.27 -.31 -.38
Shoulder Flexion
.52 .60* .51 .44
Elbow Flexion
.47 -.02 .19 .4
*significance correlation, p<.05
62
Figure 20
Positive Linear Relationship Between Absolute Back Squat 1RM and Dorsi Flexion ROM
r(9)=.62, p=.041
0
50
100
150
200
250
300
350
400
0 5 10 15 20 25 30
1R
M B
ack
Squ
at (
lbs)
Dorsi Flexion ROM (Degrees)
63
Figure 21
Positive Linear Relationship Between Absolute Conventional Deadlift 1RM and Dorsi
Flexion ROM r(9)=.58,p=.048
0
50
100
150
200
250
300
350
400
450
0 5 10 15 20 25 30
1R
M C
on
ven
tio
nal
De
adlif
t (l
bs)
Dorsi Flexion ROM (Degrees)
64
Figure 22
Positive Linear Relationship Between Absolute Back Squat 1RM and Shoulder Flexion
ROM r(9)=.60,p=.039
0
50
100
150
200
250
300
350
400
0 20 40 60 80 100 120 140
1R
M B
ack
Squ
at (
lbs)
Shoulder Flexion ROM (Degrees)
65
Relative Strength
Using the data collection from all twelve firefighters Pearson correlations were
calculated comparing all relative strength ratios in the bench press, back squat, conventional
deadlift, and pull up with each of the mobility values (ROM) in dorsi flexion, plantar
flexion, standing knee flexion, hip flexion, shoulder flexion without shoulder girdle
engagement, and elbow flexion (Table 5). Only the data of the eleven firefighters who
complete the entire study was used for the lower body strength correlations. There were
significant, moderate negative correlations observed between relative strength ratio for the
back squat and plantar flexion ROM r(9)= -.66, p=-.026 (Table 6, Figure 23), and a low
negative correlations observed for comparison between relative strength ratio for the
conventional deadlift with ankle plantar flexion r(9)= -.61, p=-.036 (Table 5, Figure 24). A
significant moderate to high correlation was seen between relative strength ratio in the back
squat and shoulder flexion ROM r(9)=.70, p=.017, (Table 5, Figure 25).
66
Table 5
Correlations for Relative Strength Ratios and Degrees ROM in Firefighters
Bench Press Back Squat
Conventional
Dead Lift
Pull Up
Dorsi Flexion
.12 .50 .37 .02
Plantar Flexion
-.22 -.66* -.61* -.49
Knee Flexion
.41 .22 .35 .53
Hip Flexion
.29 .09 .13 .37
Shoulder
Flexion
.51 .70* .52 .49
Elbow Flexion
.39 -.06 .09 .34
*significance correlation, p<.05
67
Figure 23
Negative Linear Relationship Between Relative Strength Ratio for the Back Squat and
Plantar Flexion ROM r(9)= -.66, p=-.026
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30
Re
lati
ve S
tre
ngt
h R
atio
Bac
k Sq
uat
Plantar Flexion ROM (Degrees)
68
Figure 24
Negative Linear Relationship Between Relative Strength Ratio for the Conventional
Deadlift and Plantar Flexion ROM r(9)= -.61, p=-.036
0
0.5
1
1.5
2
2.5
0 5 10 15 20 25 30
Re
lati
ve S
tre
ngt
h R
atio
Co
nve
nti
on
al D
ead
lift
Plantar Flexion ROM (Degrees)
69
Figure 25
Positive Linear Relationship Between Relative Strength Ratio for the Back Squat and
Shoulder Flexion r(9)=.70, p=.017
0
0.5
1
1.5
2
2.5
0 20 40 60 80 100 120 140
Re
lati
ve S
tre
ngt
h R
atio
Bac
k Sq
uat
Shoulder Flexion ROM (Degrees)
70
CHAPTER V
DISCUSSION
The purpose of this investigation was to identify the relationship between relative
muscular strength and joint mobility in firefighters. It was hypothesized that those
firefighters with increased mobility would have a greater relative strength; conversely, the
firefighters who had decreased mobility will also have lower relative strength. Twelve
Charleston Illinois Fire Department Firefighters volunteered and participated in the study.
This study examined strength by testing firefighters with the back squat as a lower
body push, a conventional deadlift as a lower body pull, and bench press as an upper body
press. Mobility was assessed using a Leighton Flexometer to measure joint range of motion
(ROM) in different active movement patterns.
Relative Strength and Joint Mobility
The hypothesis that there would be a significant, positive correlation between
strength and mobility was largely unsupported by the results of this study, as a majority of
the strength|mobility comparisons resulted in low to negligible, non-significant correlations.
Negative correlations were found for the relationships between both the back squat relative
strength and the conventional dead lift relative strength with increased plantar flexion ROM.
This finding suggests that greater relative strength in these two lifts are associated with a
lower ROM in plantar flexion. This finding contradicts the hypothesis that there would be a
positive correlation between relative strength and mobility.
71
While this finding may appear to contrary to what was hypothesized, during the
motion of a squat, the ankle moves from a neutral position into a range of dorsi flexion with
the tibialis anterior muscle contracting (Case et.al., 2020). Depending on a person’s
anatomy, deadlifts are the opposite of a squat. Starting the exercise in a range of ankle dorsi
flexion and returning to a neutral ankle (Ferland et.al., 2020). Decreased plantar flexion has
a negative correlation with the back squat because of the principle of muscle co-contraction.
Muscle co-contraction is the simultaneous contraction of agonist and antagonist muscles
crossing a joint (Smith, 1981). In a single joint during movement, an antagonist muscle is
inhibited to allow an agonist muscle to work fluently which is referred to as reciprocal
inhibition (Yavuz et.al., 2018). During compound exercises such as the back squat and
deadlift, muscle co-contraction is essential for joint stabilization during performance of
these exercises. The decreased ROM in plantar flexion could be attributed to co-contraction
during these two exercises, which would provide an possible explanation for this negative
correlation between variables. Conversely, an increased ROM in plantar flexion may result
in decreased relative strength due to co-contraction of the gastrocnemius and soleus creating
a small amount of movement which would cause instability of the exercises. It is believed
that the medial head of the gastrocnemius acts as dynamic knee stabilizer during squatting,
helping to offset knee valgus movements as well as limiting posterior tibial translation (Bell
et.al., 2008). This may then result in decreased relative strength ratios for the back squat and
deadlift exercises.
The findings of the correlation with decreased back squat relative strength and
plantar flexion ROM can be related to other studies in the literature. A recent study
investigated the kinematics and muscle activity during the sticking region of back squats
72
(Van den Tillaar et.al., 2020). This study was conducted very similarly to the present study.
In a single testing session, the subjects performed 5RM movements using high bar and low
bar back squats, where absolute load, descent depth, and stance width were matched
between squat conditions (Van den Tillaar et.al., 2020). The final repetition was analyzed
using 3D kinematics and electromyography (EMG) around the sticking region. The findings
of this study showed that during the low bar back squat, the soleus muscle activation was
decreased significantly with forward trunk lean in the squat causing instability of the lower
leg (Van den Tillaar et.al., 2020). This study showing that soleus muscle activation will
decrease with forward trunk lean in the squat causing instability of the lower leg.
Theoretically a decrease in squat strength could be because of the inability to sufficiently
stabilize larger loads from the floor to the knee joint. The same study also discovered that
with a high bar back squat technique, the quadriceps muscle group activation was increased
with lower erector spinae activation (Van den Tillaar et.al., 2020). This indicates that an
upright chest position during the squat is most ideal for increased external load because the
goal of achieving maximal activation of the knee extensors. Increased plantar flexion ROM
having a decreased relative strength ratio in the back squat because muscle activation will be
decreased in the soleus causing instability which leads to trunk forward lean to occur. The
increased forward lean during the squat is the reason for decreased loading which all started
with stabilization in the lower leg which could be the cause of the decreased relative strength
in the back squat and increased plantar flexion ROM.
A possible explanation as to why the findings of this study showed a significant
correlation between a decreased conventional deadlift relative strength ratio and increased
plantar flexion ROM may also be described by the findings of a previous study. Escamilla
73
et. al, (2001) analyzed the Biomechanics of athletes at the 1999 Special Olympic World
Games. During this study they analyzed position angles of joints during the conventional
and sumo deadlifts. The researchers of this study used two synchronized video cameras to
collect 60 Hz of data from 40 subjects. Parameters were quantified at barbell liftoff (LO),
when the barbell passed the knees (KP), and at lift completion (Escamilla et. al, 2001). The
findings of this study showed the sumo deadlift may be more effective in working ankle
dorsiflexors and knee extensors, whereas the conventional deadlift may be more effective in
working ankle plantar flexors and knee flexors (Escamilla et. al, 2001). The findings of this
study could provide an explanation for why the relative strength ratio in the conventional
deadlift is decreased when plantar flexion ROM is increased. The plantar flexor musculature
during the concentric phase of the conventional deadlift is performing and eccentric
contraction. Eccentric muscle contractions will illicit greater muscle damage than concentric
contractions (Häkkinen et. al, 1981; Proske & Morgan, 2001; Tøien et. al, 2018). Eccentric
exercise can cause subjects muscles to become stiff and sore after exercise because of
damage to muscle fibers (Proske & Morgan, 2001). This damage is known as Exercise
Induced Muscle Damage (EIMD) and Delayed-Onset Muscle Soreness (DOMS) which are
types of ultrastructural muscle injury (Hotfiel et.al., 2018; Hody et. al., 2019). The
conventional deadlift sufficiently activates plantar flexor musculature to contract
eccentrically which will lead to increased muscle damage and stiffness because of EIMD
and DOMS. The conventional deadlift exercise may possibly cause stiffing of plantar flexor
muscle due to the eccentric loading during the concentric phase of the conventional deadlift.
Possibly explaining the correlation between increase plantar flexion ROM and decreased
relative strength ratio in the conventional deadlift.
74
A significant, moderate positive correlation was observed between relative back
squat strength and shoulder flexion ROM. This indicates that those with greater shoulder
flexion ROM had a greater relative back squat strength. The results of this study showed an
increase in shoulder flexion ROM correlating with an increase in relative strength ratio in
the back squat. This finding supports the hypothesis that there would be a greater ROM
observed in those with greater relative strength. During a barbell back squat as performed
by all subjects in this study it is a necessity for the subjects to have the ability to externally
rotate their shoulder. Shoulder external rotation ROM was not assessed during this study but
increases in shoulder flexion ROM may be predictive of increased ROM with shoulder
external rotation (Cibulka et.al., 2015; Johnson et.al., 2019). External rotation of the
shoulder is important during a squat to protect the spine and keep the thoracic spine vertical.
Because the lumbar spine is better able to handle compressive forces than shear, a normal
lordotic curve should be maintained in this region, with the spinal column held rigid
throughout the movement (Schoenfeld, 2010; Toutoungi et.al., 2000). Increased shoulder
external rotation will allow the shoulders to be immediately inferior under the barbell rather
than anterior to the barbell. The elbows being directly below the bar will facilitate proper
spinal alignment (Dionisio et.al., 2008; Schoenfeld, 2010). When performing a squat, the
trunk kept as upright as possible to minimize shear. No lateral movement should take place
at any time (Schoenfeld, 2010). The significance between shoulder flexion ROM and the
back squat could be due to having increased shoulder ROM will allow the thoracic spine of
the squatter to maintain a more upright position in the squat being able to achieve heavier
loads. The biomechanics of this lift may explain this relationship between shoulder flexion
ROM and relative strength ratio of the back squat.
75
Absolute Strength and Joint Mobility
There was a significant, moderate positive correlation between ankle dorsi flexion
ROM and 1RM back squat. The higher ranges of motion achieved in Dorsi flexion reflected
the higher 1RM back squat in pounds. It was found that firefighters who exhibited reduced
range of motion at the ankle joint had a predisposition to excessive medial knee
displacement. Excessive medial knee displacement was found to be associated with a
clinically meaningful 20% reduced range of motion in dorsiflexion while squatting-a finding
that was attributed in part to tightness of the soleus (Bell et.al., 2008). They also showed the
medial knee displacement group exhibited tight and weak ankle musculature which
correlated with squat strength. The authors concluded that improvements to ankle ROM
may improve kinematics during a squat (Bell et.al., 2008). The ankle musculature plays a
critical role in the ability to perform a squat and may explain, at least in part, the finding of a
significant correlation between increased Doris flexion ROM and 1RM back squat.
To compare this to another study, Fuglsang et.al., (2017) investigated trunk lean in
the barbell back squat. The purpose of this study was to investigate how ankle mobility and
the segment ratios between the thoracic spine, thighs, and shanks influence the trunk angle
in the back squat (Fuglsang et.al., 2017). Eleven male subjects performed 3 repetitions at
approximately 75% of 1 repetition maximum in the squat to a parallel position (thighs
horizontal) or lower while being their motion captured on camera. The subjects performed a
weight bearing lunge test to determine maximal range of motion ROM of the ankle joint.
The findings of this study suggested that ankle mobility was significantly negatively
76
correlated with trunk angle, thereby showing that a subject with greater ankle ROM had a
more upright torso in the parallel squat position (Fuglsang et.al., 2017).
The correlation between increased conventional deadlift strength and increased dorsi
flexion ROM may be related to the increase in absolute strength in the individual
firefighter’s posterior chain. The posterior spine muscle chain consists of the thoracic,
lumbar and hip extensor muscles (De Ridder et.al., 2013). The posterior chain contributes to
increased lower body strength and power. Seeing the correlations be similar results to that of
the back squat was to be expected because both exercises entail lower body strength and is
the reason to the similarity in correlations.
Nigro & Bartolomei, (2020) investigated the comparison between the squat and the
deadlift in lower body strength and power training. The researchers of this study goal was to
compare the effects of two resistance training programs including either a deadlift or a
parallel squat on lower body maximal strength and power in resistance trained males. This
study included a total of 50 subjects, 25 that were assigned to a deadlift group and 25 that
were assigned to a squat group that trained for 6 weeks. They reexamined 1RM strength in
both lifts and jump performance after 6 weeks of training. The finding of this study showed
results indicating that both the squat and the deadlift can result in similar improvement in
lower body maximal strength and jump performance and can be successfully included in
strength training programs (Nigro & Bartolomei, 2020). This study shows the direct
correlation that back squat strength and conventional deadlift strength have a linear
relationship. Increased conventional deadlift 1RM strength will lead to an increase in 1RM
back squat strength. The converse relationship exists increased 1RM back squat strength will
lead to an increase in 1RM conventional deadlift strength. These findings may suggest why
77
both the conventional deadlift and the back squat had similar correlations with mobility in
some of the joints due to the linear relationship that exists between the conventional deadlift
and the back squat (Ferland et.al., 2020).
Ebben et.al., (2008) examined this linear relationship between the back squat and
conventional deadlift. The purpose of the study was to determine whether there is a linear
relationship between the squat and a variety of quadriceps resistance training exercises for
the purpose of creating prediction equations for the determination of quadriceps exercise
loads based on the squat load. The researchers of this study investigated six-repetition
maximums (6RMs) of the squat, as well as four common resistance training exercises that
activate the quadriceps including the deadlift, lunge, step-up, and leg extension, were
determined for each subject. The subjects that they used were 21 male college students.
After data collection they analyzed the data from the 6RMs of all the subjects were
correlated with the deadlift and squat. Results indicated a linear relationship (Ebben et.al.,
2008). The linear relationship between the two exercise as the 6RM shows that multi-
repetition maximums are similar to 1RM with these two exercises (Andersen et.al., 2014;
Calatayud et.al., 2015; Ebben et.al., 2008; Saeterbakken et.al., 2017; Saeterbakken &
Fimland, 2013).
The last significant correlation observed was between shoulder flexion ROM and
absolute back squat 1RM. Shoulder external rotation ROM was not assessed during this
study but increases in shoulder flexion ROM may be predictive of increased ROM of
shoulder external rotation. External rotation mobility of the shoulder is important during a
squat to protect the spine. Because the lumbar spine is better able to handle compressive
force than shear, a normal lordotic curve should be maintained in this region, with the spinal
78
column held rigid throughout the movement (Schoenfeld, 2010; Toutoungi et.al., 2000).
Increased shoulder external rotation will allow the squatters shoulders to be immediately
inferior under the barbell rather than anterior to the barbell. The elbows being directly below
the bar will cause proper spinal alignment is facilitated by maintaining a straight ahead or
upward gaze, which reduces the tendency for unwanted flexion (Dionisio et.al., 2008;
Schoenfeld, 2010). When performing a squat, the trunk maintained as upright as possible to
minimize shear. No lateral movement should take place at any time (Schoenfeld, 2010). This
account for the correlation between increased shoulder flexion ROM and absolute back
squat strength.
The present study did identify a result that is supported by other studies from the
research literature. That improved Dorsi Flexion ROM can improve squat kinematics
leading to improve squat 1RM when proper loading progressions are used (Case et.al., 2020;
Dionisio et.al., 2013; Ferland et.al., 2020; Schoenfield, 2010; Wisløff et.al., 2004). This
study also found previously discovered conclusion on shoulder mobility and its impacts on
squatting. Similar to the findings of studies that investigated the Functional Movement
Screening showed increased shoulder mobility will impact the scoring of the deep squat just
as in this study increased shoulder mobility predicted both relative and absolute strength
increases in eleven out of twelve Charleston Illinois Fire Department Firefighters who
volunteered and participated in the study.
79
CHAPTER VI
SUMMARY AND CONCLUSION
The purpose of this investigation was to identify the relationship between relative
muscular strength and joint mobility in firefighters. It was hypothesized that those
firefighters with increased mobility would have a greater relative strength; conversely, the
firefighters who had decreased mobility will also have lower relative strength. Twelve
Charleston Illinois Fire Department Firefighters volunteered and participated in the study.
This study examined strength by testing firefighters with the back squat as a lower body
push, a conventional deadlift as a lower body pull, and bench press as an upper body press.
Mobility was assessed using a Leighton Flexometer to measure joint range of motion
(ROM) in different active movement patterns. Few studies have examined the relationship
between relative strength and mobility in firefighters. Most research is focused on absolute
strength in this population but did not examine relative strength or mobility. Relative
strength is an essential element to a firefighter’s daily work because of the weight of the
restrictive gear they carry and wear when fighting fires.
Summary of Findings
1. Significant correlations were observed between increased absolute strength in the
back squat and increased ROM in dorsi flexion.
2. Significant correlations were observed between increased absolute strength in the
conventional dead lift and increased ROM in Dorsi flexion.
80
3. Significant correlations were observed between increased absolute strength in the
back squat and increased ROM in shoulder flexion.
4. Significant correlations were observed in decreased relative strength ratio in the back
squat and increased plantar flexion ROM.
5. Significant correlations were observed in decreased relative strength ratio in the
conventional dead lift and increased plantar flexion ROM.
6. Significant correlations were observed in increased relative strength ratio in the back
squat and increased shoulder flexion ROM.
Conclusion
It was concluded that increased joint mobility does not illicit increased relative
strength in firefighters except in specific joints and exercises. Shoulder flexion ROM
correlated with increased relative strength of the back squat in firefighters was the one
exception to the findings of this study.
Recommendations for Future Studies
Future study in this area should attempt to include a larger subject pool with more
diversity than in the present study. The demographic of these firefighters was not extremely
diverse with all of the participants being Caucasian males. Also having a subject pool of
trained and untrained subjects and comparing the results would be important for future
investigators. In addition to increasing the number of subjects included in the study,
increasing the absolute range of strength and mobility among subjects would improve the
ability to identify any relationships that might exist.
81
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APPENDICES
APPENDIX A-Informed Consent Form
Research Informed Consent
TITLE OF STUDY
Relative Strength and its Relationship with Mobility in Firefighters
PRIMARY RESEARCHER
Name – Samuel C Nozicka
Department – Eastern Illinois University Kinesiology, Sport, and Recreation
Address – 1023 Lantz Arena, Charleston, IL 61920
Phone – 847-594-2755
Email – [email protected]
PURPOSE OF STUDY
To identify the relationship between relative muscular strength and joint mobility in
firefighters.
PROCEDURES
Participants Body Weight: weight will be taken on a scale in pounds.
Strength Testing: 5 repetition maximum estimate of maximal strength: Bench press, Pull up,
Back Squat, and Deadlift.
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Range of Motion Testing: While wearing a small device that records range of motion
(Leighton Flexometer) the following joint movements will be performed: active plantar
flexion and active dorsi flexion, (movements of the ankle) active straight leg flexion and
extension (movements of the hip), active standing shoulder flexion and extension without
shoulder girdle engagement, active flexion and extension of the Humeroulnar joint
(movements of the elbow). You will be asked to move these joints as far as you are able
without pain.
RISKS
The risks involved with participation in this study are minimal. The activities you will
asked to complete for this study are similar in intensity to the physical activity you
encounter on a daily basis in your profession as a firefighter and leisure activities or less.
The type of injury most often seen with resistance and mobility activities such as those used
with this research project include musculoskeletal injury such as strains and sprains. These
risks will be further minimized by thorough instruction in performing the movements and
exercises, close supervision for proper technique, utilization of safety equipment (e.g. squat
rack) where appropriate and close communication with subjects
BENEFITS
Determining the relationship between relative strength and mobility in this population may
provide the insight to improve performance, prevent injuries and fatalities. Helping
firefighters to be more physically fit for duty creates safer communities for everyone. With
this information training programs for firefighters can be refined even more to meet their
specific needs.
Participant’s Initials: ________
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CONFIDENTIALITY
Please do not write any identifying information.
Every effort will be made by the researcher to preserve your confidentiality including the
following:
Assigning subject numbers for participants that will be used on all research notes and
documents instead of their names. Names and subject numbers will only be paired on a
master list of subjects that will be kept separate from any subject data.
All participant information will be stored in a locked file in the possession of the researcher.
CONTACT INFORMATION
If you have questions at any time about this study, or you experience adverse effects as the
result of participating in this study, you may contact the researcher whose contact
information is provided on the first page. If you have questions regarding your rights as a
research participant, or if problems arise which you do not feel you can discuss with the
Primary Researcher directly by telephone at 8475942755 or at the following email address
Given the procedures that will be utilized in this study and the safety precautions provided,
subjects are considered to be exposed to only minimal risk for injury. However, any injury
would likely be musculoskeletal in nature such as strains or sprains. If these occur, subjects
will be instructed to seek the advice of their personal health care provider if they have
concerns or if the injury appears to constitute a medical emergency, Emergency Medical
Services will be contacted immediately by calling 911.
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VOLUNTARY PARTICIPATION
Your participation in this study is voluntary. It is up to you to decide whether or not to take
part in this study. If you decide to take part in this study, you will be asked to sign a consent
form. After you sign the consent form, you are still free to withdraw at any time and without
giving a reason. Withdrawing from this study will not affect the relationship you have, if
any, with the researcher, your employer or EIU. If you withdraw from the study before data
collection is completed, your data will be returned to you or destroyed.
Participant’s Initials: ________
CONSENT
I have read and I understand the provided information and have had the opportunity to ask
questions. I understand that my participation is voluntary and that I am free to withdraw at
any time, without giving a reason and without penalty. I understand that I will be given a
copy of this consent form. I hereby give my voluntary, informed consent to participate in
this research project.
Participant's Signature _____________________________ Date __________
Researcher/Witness Signature _____________________________ Date __________
Participant’s Initials: ________
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APPENDIX B- Health History Questionnaire
HEALTH HISTORY QUESTIONNAIRE
All questions contained in this questionnaire are strictly confidential
Subject Number
M
F
DOB:
PERSONAL HEALTH HISTORY
Diagnosed diseases
or disorders
Cardiovascular disease, Pulmonary disease, Diabetes, Hypertension, Kidney disease,
Neurological, Cancer, Muscular disorders, Arthritis, Covid-19(????), etc….
List any medical problems that are not listed above.
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List your prescribed medications and over-the-counter drugs or supplements
109
Name the Drug
Allergies to medications
Name the Drug
HEALTH HABITS AND PERSONAL SAFETY
All questions contained in this questionnaire are optional and will be kept strictly confidential.
Exercise Sedentary (No exercise)
Mild exercise (i.e., climb stairs, walk 3 blocks, golf)
Occasional vigorous exercise (i.e., work or recreation, less than 4x/week for 30 min.)
Regular vigorous exercise (i.e., work or recreation 4x/week for 30 minutes)
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Diet Are you dieting? Yes No
If yes, are you on a physician prescribed medical diet? Yes No
Caffeine None Coffee Tea Cola
# of cups/cans per day?
Participant's Signature _____________________________ Date __________
Researcher/Witness Signature _____________________________ Date __________
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APPENDIX C-Recruitment Flyer
Be a Participant!
Help to identify the relationship between relative strength
and joint mobility in firefighters.
Student Researcher
Sam Nozicka
PARTICIPANT PROCESS INCLUDES:
-Pre-screening information
-One session (approximately 1-hour)
• Range of motion examination
• Strength testing (5-repetition
maximum) Research Committee
Dr. Brian Pritschet
Mrs. Maranda Schaljo
Mr. Joshua Stice