The effect of structural firefighter protective clothing systems on single-legged functional hop test scores

Abstract

BACKGROUND:

Firefighters must complete a physical ability test to assess work readiness. There is a lack of understanding of how personal protective clothing (PPC) affects functional performance tests for work readiness, e.g. Triple Hop for Distance (THD) and Triple Hop for Work (THW).

OBJECTIVE:

To examine firefighter PPC’s effect on the THD and THW measures.

METHODS:

Thirty-one healthy, untrained participants (male = 20, female = 11; age = 23±3 years; height = 175.30± 11.12 cm; mass = 77.94±14.24 kg; mass in PPC = 89.14±14.68 kg) completed three successful trials of the THD on their dominant and non-dominant leg, with and without PPC. The main outcome measures included maximum and mean distances on the THD with and without PPC and THW.

RESULTS:

We identified a significant decrease in THD measures (mean difference = 97.83 cm; p < 0.001) and THW measures (mean difference = –326.61J; p < 0.001) when donning PPC in the dominant leg. We identified a significant decrease in THD (mean difference = 121.48 cm; p < 0.001) and THW (mean difference = 493.15J; p < 0.001) for females, and a significant difference for THD (mean difference = 84.83 cm; p < 0.001) for males when donning PPC.

CONCLUSIONS:

The addition of PPC decreased the THD and THW measures. The additional mass of the PPC required the more energy to move the same distance without the PPC.

Keywords

Tactical athlete work readiness occupational health

1. Introduction

In 2015, the National Fire Protection Association reported that the United Stated Fire Service employed over 1.1 million firefighters [1]. Of these individuals 30% were considered career firefighters while over 800,000 firefighters were considered volunteer [1]. Despite the disparity in number of career and volunteer firefighters, each individual must begin the process of becoming a firefighter in a similar manner. Individuals interested in becoming a volunteer or career firefighter must possess mental and physical strength sufficient to complete the critical tasks of the job [2, 3]. The need for health and wellness ignited a discussion in 1996 regarding firefighter’s not being physically capable of performing tasks related to the fire service [4]. As a result, the Candidate Physical Ability Test (CPAT) program was developed as an assessment for qualification as a firefighter through job readiness [5]. The CPAT seeks to simulate eight job-specific tasks that incorporate the major areas of physical fitness including muscular strength, muscular endurance, flexibility, and cardiopulmonary endurance [5]. The critical tasks that are incorporated into the CPAT include a stair climb, hose drag, equipment carry, ladder raise & extension, forcible entry, victim search & rescue, and ceiling breach & pull [5]. The CPAT is performed as a sequence of events and assessed in a pass/fail manner based on finishing the program under 10 minutes and 20 seconds [5]. The candidate must wear long pants, a hard hat with chin strap, work gloves and footwear to loosely simulate the additional mass and burden of firefighter personal protective clothing (PPC) worn on the job [5]. Additionally, the candidate must don a 50-pound (22.7 kg) weighted vest to replicate the weight of a self-contained breathing apparatus and PPC during the eight tasks, with two additional 12.5-pound weights on each shoulder for the stair climb event [5]. The addition of the vest and weights are to replicate the effects that the additional load carriage that is created from the self-contained breathing apparatus and ensemble may have on the physical performance of the candidate.

The typical PPC for the fire service includes a helmet, coat, trousers, boots, protective gloves and flash hood as set forth by the National Fire Protection Association 1500: Standard on Fire Department Occupational Safety and Health Program mandate [6]. Interestingly, a firefighter will never complete any of the CPAT tasks, such as ladder carry or stair climb, while wearing only long pants and a vest, because of the protective clothing standard. This means that individuals are deemed physically ready to perform the job-specific tasks of firefighting without ever donning firefighter PPC. Previous research identified that the weighted vest did not replicate the cardiovascular endurance necessary to perform the events as compared to wearing the PPC [7]. As a result, the candidate or rookie firefighter may be entering the fire service at an increased risk for injury due to the lack of familiarity with the functional movement restrictions and additional weight limitations that the PPC may add while completing tasks of the job [8].

While the CPAT has sought to improve the work readiness of an individual through a timed series of tasks, fire departments, specifically volunteer stations, have the freedom to use the CPAT as part of the entrance requirements, or to select other measures for their evaluation, or to not incorporate any assessments prior to someone joining the fire service. Additionally, there are limitations of the program that have identified a critical need to improve or reimagine the assessment process for a candidate entering the fire service. The CPAT seeks to assess and measure the cardiovascular fitness of an individual through a time series of skills on a pass or fail basis [9, 10]. Of the eight events in the CPAT, seven tasks are designed to evaluate the lower extremity muscular strength, in combination with anaerobic and aerobic capacity systems [5]. Although lower extremity strength is necessary to complete the tasks of the CPAT, the specific measures of muscular strength, endurance, and power are not collected as a means of baselines data to identify individuals at risk of injury or to assist with maintenance of physical fitness throughout the career of the firefighter [5].

Several methods are available to clinicians and occupational health practitioners to assess muscular strength such as isokinetic dynamometry, hand-held dynamometry, graded isolated isometric strength tests, and one-repetition maximum testing [11 –13]. One other valid predictor of lower extremity strength and power in healthy individuals is functional performance testing [14]. Functional performance testing seeks to replicate static or unidimensional strength assessments through movements such as hopping and jumping. This population is of interest, as all individuals entering the recruit academy to become a firefighter must self-identify as “healthy”, meaning no current injuries or illnesses. As a result, one such functional performance test to assess baseline muscular strength and power is the use of single-legged hop test like the Triple Hop for Distance (THD). The THD is a specific single-legged hop test that measures the strength and power of the lower extremity to either healthy individuals or those recovering from knee injuries [14, 15]. This single-legged functional hop test seeks to measure lower extremity strength and power, similarly to that of the CPAT tasks, but has the advantage of using less equipment and space, and is easily administered. In addition, the Triple Hop for Work (THW) allows the short test of the THD be calculated for longer duration activities regarding expected energy expenditure.

While the literature supports the notion that the addition of PPC for firefighters affects their static and dynamic balance, there is a need to understand how the PPC may affect the functional performance tests, such as THD measures, in active individuals without formal training as a firefighter prior to adopting or suggesting the use of these tests in the fire service [16 –18]. As a result, the purpose of this study was to investigate the THD and THW while donning and doffing PPC and comparisons of the measures based on the sex of the individual.

2. Materials and methods

Thirty-one healthy participants (male = 20, female = 11) were recruited through flyers and word of mouth to participate in this study. We included participants with no reported chronic health conditions or lower extremity injuries within the last six months. All participants had to self-report as physically active, which equated to engaging in more than 200 minutes per week of physical activity and/or exercise-related activities [19]. In addition, the participants could not currently be or have formal training as a firefighter in any capacity. This population was selected as our target demographics to replicate the novice firefighter, either recruit or volunteer, which do not have the experience wearing and moving within the PPC much unlike trained, career firefighters. Additionally, previous research relative to firefighter strength testing have used a similar population of civilians [12, 13]. All participants signed an informed consent prior to inclusion. This study was approved by the Indiana State University Institutional Review Board.

2.1. Procedures

Data was collected in one session per subject, by one investigator, in a research laboratory. Following the signed consent of the participant, anthropometric and demographic information were collected. Next, the participant’s leg dominance was evaluated using the Functional Leg Dominance (FLD) assessment [20]. Each participant had data recorded for the single-legged functional performance test on their dominant and non-dominant leg. In addition, randomization of clothing system worn (+PPC = donning the personal protective clothing; -PPC = in athletic wear) and the leg tested were completed to assess the effect that PPC had on a single-legged functional performance test.

2.2. Triple hop for distance

For the single-legged functional performance test, we utilized the THD test. The THD is a reliable measure of lower extremity strength and power as compared to isokinetic dynamometry and vertical jump measures in a healthy population [14]. The testing procedures for the THD test were adopted from previous research in a healthy population [14]. We allowed participants a five-minute self-directed bike warm-up prior to data collection. We required participants one to three practice trials, based on previous methodology, prior to the recorded sessions for each dependent variable [14]. Self-rest was allowed in-between each session to allow participants to rest preventing fatigue. The self-rest time was not monitored as we allowed the period to be used for donning and doffing of the PPC, but all participants received a verbal reminder to take a period of self-rest between testing scenarios. We measured the distance from the start marker to the heel of the foot if the participant maintained balance at the conclusion of the final hop. Unsuccessful attempts were recorded if the participant did not complete the trial as instructed, lost balance during any portion of the test, and/or could not hold the final stance on the single leg for at least two seconds. We placed no cap on the number of unsuccessful attempts, and provided a brief statement as to why the trial was considered an unsuccessful attempt for educational purposes. The first three acceptable trials were recorded, and the maximum and mean distance were used for data analysis. An example of the THD is available in Fig. 1. Additionally, we calculated THW as a follow-up calculation. THW, measured in joules, was calculated by multiplying the THD (in meters) by the mass of the participant with and without PPC (in kilograms) and gravity (9.8 meters/second²) [21].

Fig.1

Triple Hop for Distance in Personal Protective Clothing. The starting position is noted on the top and the first hop is noted on the bottom.

2.3. Statistical analysis

Data was transferred into a custom spreadsheet (Microsoft Excel 2010, Microsoft Corp., Redmond, WA) and analyzed using the Statistical Package for Social Sciences version 23 (IBM Corp. IBM SPSS Statistics for Windows, Version 23.0. Armonk, NY: IBM Corp.) Descriptive data (means and standard deviations) were analyzed for all demographic and variable measures. Independent samples t-tests were used to compare the means of the THD and THW with and without the PPC. Additionally, we separated the data by sex for follow-up paired samples t-tests analysis for comparisons of THD and THW measures with and without the PPC. To examine the effect of firefighter PPC with THD measures, paired-sample t-tests with Holms’ sequential Boneferroni adjustments were used. The significance level was set α priori at p≤0.05.

3. Results

Thirty-one individual participated in this study. Table 1 provides demographic measures of interest for the participants separated by sex. Overall, the calculated mass of PPC itself was 11.20±0.97 kg.

Table 1
Participant demographics

Measure Females (n = 11, 35.5%) Males(n = 20, 64.5%) Total (n = 31, 100%)

Age 23±1 years 23±3 years 23±3 years

Height 167.7±4.67 cm 179.48±11.49 cm 175.30±11.12 cm

Mass 67.08±9.78 kg 83.91±12.80 kg 77.94±14.24 kg

Mass in PPC 77.85±9.66 kg 95.34±13.30 kg 89.14±14.68 kg

Leg Dominance Left –0, 0.0% Left –2, 10.0% Left –2, 6.5%

Right –11, 100% Right –18, 90.0% Right –29, 93.6%

Measure	Females (n = 11, 35.5%)	Males(n = 20, 64.5%)	Total (n = 31, 100%)
Age	23±1 years	23±3 years	23±3 years
Height	167.7±4.67 cm	179.48±11.49 cm	175.30±11.12 cm
Mass	67.08±9.78 kg	83.91±12.80 kg	77.94±14.24 kg
Mass in PPC	77.85±9.66 kg	95.34±13.30 kg	89.14±14.68 kg
Leg Dominance	Left –0, 0.0%	Left –2, 10.0%	Left –2, 6.5%
	Right –11, 100%	Right –18, 90.0%	Right –29, 93.6%

Demographic Measures. cm: centimeters; SD: standard deviation.

We did not identify any significant differences when comparing the dominant to the non-dominant leg while donning PPC (p = 0.594) or doffing PPC (p = 0.678) for the THD measures, thus allowing for symmetrical single-legged hop distances within each participant. As a result, we will only report dominant leg data for the remaining analyses. Table 2 provides mean and standard deviations for all variables of interest.

Table 2

Triple hop for distance and triple hop for work measures

	n	Mean±SD
Triple Hop for Distance (cm)	31
Dominant – PPC		456.66±77.96cm
Dominant +PPC		358.83±90.54cm
Non-Dominant – PPC		459.37±89.67cm
Non-Dominant +PPC		355.83±89.65cm
Triple Hop for Work (J)	31
Dominant – PPC		3495.94±881.07J
Dominant +PPC		3169.33±1025.20J
Non-Dominant – PPC		3506.87±909.42J
Non-Dominant +PPC		3142.53±1017.26J

cm: centimeters; J: joules; SD: standard deviation.

To examine the effect of firefighter PPC on THD measures in the dominant leg of the participants, we completed two paired-sample t-tests with Holms’ sequential Boneferroni adjustments. We identified a significant decrease in THD measures for the dominant leg when donning PPC (T₍₃₀₎ = 10.45; mean difference = 97.83 cm; 95% CI = 78.71, 116.9; p < 0.001). Figure 2 provides a scatter plot of the measures of the dominant leg for all participants.

Fig.2

Scatter plot of the dominant limb Triple Hop for Distance measures for all participants.

To examine the force and distance moved in relation to the participant’s mass with and without PPC, we calculated the Triple Hop for Work (THW). The THW data was analyzed using the THD measure, gravity, and mass of the individual with and without PPC. We identified a significant decrease in work when donning PPC for the dominant leg (T₍₃₀₎ = –3.963; mean difference = –326.61J; 95% CI = –494.93, –158.29; p < 0.001).

We also analyzed the THD and THW measures as compared to the sex of the participants. We identified a significant effect of sex on the dominant leg with and without PPC (p < 0.001) for THD and THW measures with a significant decrease in THD (T₍₁₀₎ = 9.971; mean difference = 121.48 cm; 95% CI = 94.33, 148.62; p < 0.001) and THW (T₍₁₀₎ = –3.963; mean difference = –493.15J; 95% CI = –649.71, –366.60; p < 0.001) for females when wearing PPC, and a significant difference for THD (T₍₁₉₎ = 7.005; mean difference = 84.83 cm; 95% CI = 59.48, 110.18; p < 0.001) for males. We did not identify a significant decrease in THW for males with and without PPC (T₍₁₉₎ = –1.99; mean difference = –326.61J; 95% CI = –482.23, 12.20; p = 0.061). Figure 3 provides a representation of the comparisons between – PPC and +PPC as compared to sex for THD and THW.

Fig.3

Dependent t-test mean data for the measures of Triple Hop for Distance and Triple Hop for Work +PPC and – PPC. Significance is denoted by a * at the p < 0.01 level.

4. Discussion

The primary findings of this study were that the addition of PPC reduced the single-legged functional performance test measures and required more energy to complete the tests. The results suggest that functional testing used to assess lower extremity strength and power should consider the addition of PPC for measurements as this is more applicable to the occupational setting that firefighters will experience. The results identify that any profession that dons additional gear and is required to complete physical tasks, such as police officers, military personnel, and a variety of professions that use hazardous material suits, should consider functional testing of their employees while they wear their uniforms and gear to ensure their work readiness as measures of THD and THW differed between donning and doffing PPC.

This study explored the addition of PPC in non-firefighter trained individuals. Despite the public perception regarding the fitness level of firefighters, most United States’ fire departments do not have a physical activity or physical fitness requirement after the onset of onboarding placing the firefighter and public at risk. [22, 23]. This means that firefighters may work a career as a firefighter without ever having their ability and capacity to complete functional and fitness activities. Additionally, the methodology was chosen to replicate the effect of a new load carriage on basic fire recruits entering the workforce. Previous research in tactical athletes, specifically Army ROTC Cadets, identified postural control changes due to the additional load carriage between 16–20.5 kg [24]. Currently, the CPAT requires the use of a weighted vest and arm weights to replicate the additional load during eight job specific events in a timed manner [5]. While the CPAT is job specific and time sensitive, which is necessary for firefighters, the additional weight and movement restrictions of the PPC may not be representative of a weighted vest. The weighted vest worn over the torso may not add the strain from the load to the lower extremity. In this study, we did not have the participants wear a self-contained breathing apparatus unit. Previous research on the effect of the self-contained breathing apparatus on job performance found that the additional weight was less of a factor as compared to the distribution of the weight across the back, thus the additional weight of the self-contained breathing apparatus will continually negate performance measures due the changes in center of gravity [25]. As a result, we examined the effect of the PPC including the trousers, coat, gloves, flash hood, helmet and protective boots. The weight of this gear alone weighed approximately 11.2 kg (24.7 lbs.), which is half of the mass of the weighted vest.

While the focus of this study used individuals with no formal fire training experience, we believe these finding may have implications in the health and wellness considerations for career and volunteer firefighters. Previous research highlighted that most (41.2%) of the individuals who took the CPAT during the timeline of data collection were between 25 to 29 years old [26]. This data is representative of the participants in our study, as the mean age of the participants was 23±3 years. However, most of the research within the fire service depicts the typical firefighter as overweight or obese [27]. While the sample from this study would not be defined as either of these categories, it is important to note that previous research identified that the body mass of a firefighter did not influence functional movement to a significant level when measured outside of the PPC and additional equipment [28]. This finding is important as the data from our study represents that an additional mass of 11 kg (25 lb.) from the PPC and current design of the gear may negatively affect how an individual moves during functional tests. The impact of physiological strain and functional performance deficits caused by the PPC may be influencing the high rates of cardiovascular cases and sudden cardiac death in the fire service, as more energy is necessary to complete these functional performance tasks while donning PPC [29 –31]. In order to better prevent and prepare individuals for the fire service, testing and pre-work readiness assessments should be completed in the turnout gear that will be worn during job-specific tasks as necessary factor in measuring strength, endurance and aerobic capacity [23].

4.1. Triple hop for distance

Previous research identified that the THD was a reliable measure of lower extremity strength and power [14]. In our study, we hypothesized that the addition of the PPC would negatively influence the measure of single-legged functional hop test. The results of the study identified a statistically significantly difference for all participant’s THD measures on the dominant leg. Previous research on functional performance testing for hip and thigh strength measures suggested that neuromuscular firing patterns for the THD is more similar to those of isokinetic and eccentric-strength testing [21]. As the THD is a dynamic task, there is a need for neuromuscular control that incorporates strength, endurance and balance of the lower extremity to propel the body, land and hold the stance, and complete the task a series of times. As of 2015, 22.7% of job-related injuries on the fire ground were due to slips, jumps and falls suggesting that balance, strength and neuromuscular deficits in an unideal environment are occurring [32]. The THD could be used as a measure to determine baseline functional strength to assist occupational health and fitness professionals to improve injury prevention and wellness promotion. Additionally, future research should examine the effect of previous neuromuscular control stress as a means for recruitment and job readiness. While not asked in this study, a participant who has previously donned additional gear (football, lacrosse and ice hockey athletes) during functional movements may explain a crossover effect from sport training in equipment-laden sports for the future duties required of tactical athletes donning PPC and equipment.

4.2. Triple hop for work

The calculation of THW has been suggested to be a better indicator of maximum strength and rate of force development [21]. The THW involves the mass of the individual, which is important for this study as the purpose was to assess the impact after donning PPC on a single-legged functional hop test. The results from this study identified a significant decrease in work when donning PPC for the dominant leg when comparing all participants. The data for THW demonstrates a need for assessment and training as the individual would perform job specific tasks. The THW calculation is a direct measure of the amount of energy, or work, necessary to move an object. The addition of PPC significantly impacted the work calculation during the THD test meaning that, as a whole, participants required more energy to move the same distance without PPC (mass of the participant) compared to wearing PPC (mass of participant plus mass of PPC). This finding is similar to previous research that identified that load carriage and personal protective equipment for firefighters reduced the work capacity and decreased performance [29]. As such, there is a need to consider the additional mass of the PPC in determining work readiness. Future research should examine the additional load carriage and mass per item of PPC such as the boots and trousers. The protective boots that firefighters wear differ in weight between styles whereas rubber boots, which were worn in this study, weigh approximately three pounds more than leather boots do. The rubber boots have an impact of gait including a wider stride, slower pace, and longer stance phase of both feet suggesting a longer duration for neuromuscular and postural control to balance the individual [33]. Finally, the rubber boots also affected the hip and knee joints, which have important roles in the kinetic chain of lower extremity strength. The additional mass of the rubber boots, paired with the dynamic functional alterations, may predispose firefighters to lower extremity injury as they begin in the fire service [17]. We believe this to be true as rubber boots are more affordable and may be suggested by fire department for new recruits and candidates.

4.3. Comparison of sex

According the 2015 National Fire Protection Association report, 96.5% of career firefighters were identified as male (334,050) as compared to the 3.5% (12,100) who identified as female [1]. While a sex gap exists in the fire service, the current standards in the fire service are not specific to sex as all firefighters are expected to perform the essential tasks of the job. The CPAT and other physical assessments have come under scrutiny as a fair measure of job readiness for female candidates [34, 35]. In 2000, an Austin, Texas female candidate filed a formal complaint with the United States Equal Employment Opportunity commission regarding the CPAT as a legal test in selecting firefighters, which led to the addition of two practice trials prior to the formal test in a private consultation and settlement (EEOC Charge No. 31CA00865). A National Fire Protection Association study revealed that 90% of males pass the CPAT while only 50% of females pass the CPAT [26].

In our study, we had 20 males and 11 females allowing for separation of the data into the variable of sex for comparisons of THD and THW measures while donning PPC and without PPC. Previous research has also suggested the need to separate the data for functional performance measures including that of the THD as a whole as comparisons of an entire population may overestimate the variances [21]. We identified a significant decrease in THD and THW for females while donning PPC, whereas we only identified a significant decrease in THD for male participants. Although a difference exists in THW measures for males with and without PPC, it is not significant. This means that male participants did not experience the need for additional energy to achieve the same distance with the additional mass. Although the PPC prevents fire exposure and chemical burns, the gear may be creating limitations in the ergonomics of firefighting. As males and females THD and THW measures differ with PPC, practitioners should partake in gear assessments, much like the ones that occur in equipment-laden sports such as football, to ensure gear selection and fit for the individual. Additionally, the sex differences of THW measures identify that females must work harder to compete the same tasks as men in this study, specifically even with more energy while wearing PPC. While not examined in this study, this may predispose female firefighter candidates to more cardiovascular strain and less efficiency in completing job-specific tasks.

4.4. Limitations

The study suffered from threats to external validity. The population selected for the sample were active civilians with no previous fire service or physical performance testing experience. As a result, the results from this study may not be applicable to other groups. We suggest that future research consider the effects of physical performance testing, such as the THD, in rookie firefighters to understand how this population may differ from that of the general population and career firefighters.

Additionally, the methods of the study eliminated the addition of the self-contained breathing apparatus, breathing mask, and firefighter-specific tools during the testing procedures. We suggest that future research explore movement screening respective to job-related tasks and functional movement patterns while donning all required gear of fire runs.

5. Conclusions

The addition of PPC decreased the single-legged functional hop test scores of the untrained participants. These data suggest that the THD as a functional performance measure of lower extremity strength and power while donning PPC hinders their measures, thus implying a relationship exists in which the PPC decreases the ability. Additionally, THW measures were significantly different while donning PPC as a whole, and within females and males. This suggest that the additional mass of the PPC requires the firefighter to exert more energy to move the same distance, as they would be able to do out of the PPC.

Conflict of interest

None to report.

Footnotes

Acknowledgments

The Tactical Athlete Research and Education Center and the Neuromechanics, Interventions, and Continuing Education Research (NICER) Laboratory at Indiana State University provided technical assistance for this project. This study received financial assistance from the College of Graduate and Professional Studies at Indiana State University.

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