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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

v

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 – scnozicka@eiu.edu

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: ________

105

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

scnozicka@eiu.edu.

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

scnozicka@eiu.edu

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

Blpritschet@eiu.edu

Mrs. Maranda Schaljo

mdschaljo@eiu.edu

Mr. Joshua Stice

jstice@eiu.edu