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The Effect of Fatigue and Training Status on Firefighter Performance

Dennison, Katie J.; Mullineaux, David R.; Yates, James W.; Abel, Mark G.

Journal of Strength and Conditioning Research: April 2012 - Volume 26 - Issue 4 - p 1101–1109
doi: 10.1519/JSC.0b013e31822dd027
Original Research
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Dennison, KJ, Mullineaux, DR, Yates, JW, and Abel, MG. The effect of fatigue and training status on firefighter performance. J Strength Cond Res 26(4): 1101–1109, 2012—Firefighting is a strenuous occupation that requires optimal levels of physical fitness. The National Fire Protection Association suggests that firefighters should be allowed to exercise on duty to maintain adequate fitness levels. However, no research has addressed the effect of exercise-induced fatigue on subsequent fire ground performance. Therefore, the primary purpose of this study was to determine the effect that a single exercise session had on the performance of a simulated fire ground test (SFGT). Secondarily, this study sought to compare the effect of physical training status (i.e., trained vs. untrained firefighters) on the performance of an SFGT. Twelve trained (age: 31.8 ± 6.9 years; body mass index [BMI]: 27.7 ± 3.3 kg·m−2; V[Combining Dot Above]O2peak: 45.6 ± 3.3 ml·kg−1·min−1) and 37 untrained (age: 31.0 ± 9.0 years; BMI: 31.3 ± 5.2 kg·m−2; V[Combining Dot Above]O2peak: 40.2 ± 5.2 ml·kg−1·min−1) male career firefighters performed a baseline SFGT. The trained firefighters performed a second SFGT after an exercise session. Time to complete the SFGT, heart rate, and blood lactate were compared between baseline and exercise SFGT (EX-SFGT) conditions. In the trained firefighters, time to complete the SFGT (9.6% increase; p = 0.002) and heart rate (4.1% increase; p = 0.032) were greater during the EX-SFGT compared with baseline, with no difference in post-SFGT blood lactate (p = 0.841). The EX-SFGT time of the trained firefighters was faster than approximately 70% of the untrained firefighters' baseline SFGT time. In addition, the baseline SFGT time of the trained firefighters was faster than 81% of the untrained firefighters. This study demonstrated that on-duty exercise training reduced the work efficiency in firefighters. However, adaptations obtained through regular on-duty exercise training may limit decrements in work efficiency because of acute exercise fatigue and allow for superior work efficiency compared with not participating in a training program.

1Department of Kinesiology and Health Promotion, University of Kentucky, Lexington, Kentucky

2School of Sport, Coaching and Exercise Science, University of Lincoln, Lincoln, United Kingdom

Address correspondence to Dr. Mark G. Abel, mark.abel@uky.edu.

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Introduction

Firefighting is a strenuous and dangerous occupation that places substantial stress on the anaerobic and aerobic energy systems (8,10,18,19). Specifically, performing fire ground tasks produces peak blood lactate levels between 6 and 13 mmol·L−1, relative heart rate values of 79–88% of maximal heart rate, and requires an aerobic capacity of at least 40–43 ml·kg−1·min−1 (i.e., ≈12 METs [2,8,10,19]). Furthermore, the primary causes of injury to firefighters are overexertion and strain (9). Thus, inadequate fitness levels may reduce the occupational performance and increase the risk of overexertion injuries to the firefighter.

One strategy to improve the fitness levels of fire service personnel is through participation in a regular exercise program. The National Fire Protection Association (NFPA) has recognized the importance of implementing fitness programs within the fire service and has released a document stating that “implementing a fitness program will promote the members' ability to perform occupational activities with vigor and to demonstrate the traits and capacities normally associated with a low risk of development of injury, morbidity, and mortality” (14). The NFPA has suggested that fire administrators allocate time for firefighters to participate in fitness programs while on-duty (14). This strategy may increase the likelihood that firefighters will participate in a regular fitness program. However, it is reasonable to question whether the fatigue induced by an on-duty exercise session will negatively impact subsequent job performance. To this end, it is important that fire service personnel and tactical strength and conditioning professionals clearly understand the potential physical effects that on-duty training may have on subsequent occupational performance. More clearly understanding the potential effects of exercise-induced fatigue on firefighter performance may provide a valuable insight regarding (a) the decrement in occupational efficiency because of prior exercise, (b) whether it is prudent to allow firefighters to exercise while on duty, (c) the appropriate scheduling of on-duty exercise sessions (e.g., exercise just before leaving the shift), and (d) the most appropriate exercise mode and intensity for training while on duty.

Currently, there is limited literature evaluating on-duty exercise training for firefighters. However, many fire departments across the country do allow or require firefighters to exercise while on duty. Therefore, it is important that firefighter administrators and strength and conditioning professionals understand the effects of exercise-induced fatigue on firefighter performance. Thus, the primary purpose of this study was to determine the effect of exercise-induced fatigue on the simulated fire ground performance of trained male firefighters. We hypothesized that exercising while on duty would negatively affect the efficiency of fire ground performance compared with a no-exercise baseline condition.

Furthermore, given that the NFPA recommends that firefighters engage in a regular exercise program, we felt it was important to evaluate the effect of physical training status on fire ground performance. Therefore, the secondary purpose of this study was to compare the simulated fire ground performance of trained firefighters to a group of untrained firefighters. This information would provide perspective for fire service administrators in 2 important ways: (a) it would demonstrate the effect of training status (i.e., trained vs. untrained) on fire ground performance, and (b) it would provide a unique comparison of the fire ground performance of trained firefighters after exercising to untrained firefighters in a nonfatigued state. We hypothesized that the baseline fire ground performance of the trained firefighters would be superior to that of the untrained firefighters and that the trained firefighters' postexercise fire ground performance would be similar to the nonfatigued fire ground performance of the untrained firefighters.

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Methods

Experimental Approach to the Problem

The primary purpose of this study was to determine the effect of exercise-induced fatigue on the simulated fire ground performance of trained male firefighters. Therefore, this arm of the study used a repeated measures design where the firefighters served as their own control. The trained firefighters performed the simulated fire ground test (SFGT) twice, once without the exercise session (i.e., a nonfatigued baseline condition) and a second time 10 minutes after the completion of an exercise session (i.e., fatigued condition). The 10 minute duration between the exercise session and the SFGT was selected because a short recovery time would likely produce a maximal decrement in firefighter performance and approximated the response time to go from the fitness center to an actual emergency scene. Therefore, this protocol evaluated what may be considered a “worst case” scenario regarding the potential effect of exercise-induced fatigue. The order of these testing sessions was randomized, and they were performed on nonconsecutive days. The exercise session served as the independent variable. Heart rate, blood lactate, and rating of perceived exertion (RPE) were evaluated during the baseline SFGT and exercise SFGT and served as the dependent variables. Comparisons were made between the trained firefighters' baseline SFGT and the exercise SFGT for time to completion, heart rate, post-SFGT blood lactate, and RPE.

The secondary purpose of this study was to evaluate the effect of training status on work performance. Therefore, we compared the completion time of the SFGT of a group of trained firefighters with that of a group of untrained firefighters. If exercise-induced fatigue negatively affects fire ground performance, critics may suggest that it is ill advised for firefighters to train while on duty. To this end, we felt it would be informative to compare the trained firefighters' fatigued performance (i.e., exercise SFGT condition) with that of the nonfatigued performance of untrained firefighters. Therefore, a group of untrained firefighters performed an identical SFGT once in a nonfatigued state.

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Subjects

A convenience sample of 12 trained male career firefighters was recruited to participate in this study. These subjects had been participating in a supervised on-duty exercise program for approximately 1 year before this study. Specifically, these firefighters performed about 2 exercise sessions per week, 1 hour per session, performing primarily circuit training and aerobic exercises. Therefore, the term “trained” will be used throughout this manuscript to reflect their training history. In addition, a second group of 37 male career firefighters, from the same fire department, were recruited to participate in this study to serve as an untrained reference group. This group of firefighters had not participated in supervised physical training program for at least 2 months before performing the SFGT. Some of these 37 subjects did not regularly participate in the supervised training program. The characteristics of the trained and untrained firefighters are displayed in Table 1. Note that the trained firefighters had a lower body mass and body mass index (BMI) and a higher predicted V[Combining Dot Above]O2peak compared with that of the untrained firefighters (p ≤ 0.012).

Table 1

Table 1

All the subjects were required to complete a medical examination before the study and were cleared for duty by a physician. All the subjects provided written informed consent after a detailed explanation was provided about the aims, benefits, and risks associated with the investigation. The subjects were told that they were free to withdraw from the study at any time, without penalty. All the procedures used in this study were approved by the University's Institutional Review Board before initiation of the study.

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Testing Procedures

All the testing sessions took place at the Fire Department's Training Center. During testing session 1 and 2 anthropometric measures, strength tests, and a submaximal aerobic capacity test were completed. Specifically, the subjects' standing height was measured (to the nearest 0.1 cm) without shoes, by using a stadiometer (Road Rod 214, Seca, Hanover, MD, USA). Body mass was measured (to the nearest 0.5 kg) without shoes on an electronic scale (TBF-521, Tanita Corporation, Arlington, Heights, IL, USA). The subjects' percent fat was measured using a whole-body bioelectrical impedance analyzer (BIA; Model: 310, Biodynamics Corporation, Seattle, WA, USA). Electrodes were placed on the subjects' wrist and hand, and ankle and foot while lying in a supine position. Age, sex, height, and body mass were entered into the BIA device to predict percent fat using the manufacturer's prediction equation. Resting blood pressure was measured manually via auscultation with the subject in a seated position.

The trained firefighters completed 10 repetition maximum (10RM) strength tests for all of the externally weighted exercises used in the circuit training exercise session. Specifically, 10RM tests were completed for the seated row, bench press, and deadlift exercises during the first testing session. To avoid undue fatigue of common muscles (i.e., triceps and anterior deltoid), the 10RM test for the shoulder press was completed during the second testing session. The 10RM was determined using a recognized multiple RM protocol (4). The 10RM assessment began with a warm-up of 5–10 repetitions followed by a 1-minute recovery period. Then, the load was increased, and the subject performed 10 repetitions. Next, the subject rested for 2 minutes, and an additional weight was added. Finally, the subjects performed 10 repetitions of the exercise followed by a 2-minute rest period until they could no longer repeat 10 consecutive repetitions. Most of the subjects reached their 10RM within 3–5 sets.

During the second testing session, the trained and untrained firefighters performed the Gerkin submaximal treadmill protocol to estimate peak oxygen consumption (V[Combining Dot Above]O2peak). A population-specific prediction equation was used to estimate the firefighters' V[Combining Dot Above]O2peak (20). Specifically, the protocol used the time to reach 85% of maximum age-predicted heart rate (HRmax) and BMI to predict V[Combining Dot Above]o2peak. Heart rate was measured via telemetry (Polar A1, Electro, Oy, Finland). The test began with a 3-minute warm-up, followed by increases in treadmill speed or grade each minute until the firefighter's heart rate reached 85% of the HRmax. The time required to reach 85% of the HRmax was recorded and later entered into the following V[Combining Dot Above]o2peak prediction equation: V[Combining Dot Above]O2peak (ml·kg−1·min−1) = 56.981 + 1.242 (Time to 85% HRmax [min]) − (0.805 × BMI) (20).

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Simulated Fire Ground Test

The SFGT was used as an assessment of fire ground and rescue task efficiency. To ascertain the validity of this assessment, the trained firefighters completed a questionnaire to rate how similar they felt each task was compared with performing these tasks on the fire ground using a 5-point Likert-type scale (1 = “Not relevant,” 3 = “Relevant,” 5 = “Very relevant”). According to the median response, the firefighters indicated that 6 out of the 7 tasks used in the SFGT were “very relevant.” The firefighters indicated that the forcible entry task was between “relevant” and “very relevant” (median response = 4). Furthermore, to establish the reliability of the SFGT, the trained firefighters were timed while performing the SFGT 3 times before testing, on separate days. The SFGT provided an acceptable level of test-retest reliability (intraclass correlation coefficient (ICC) = 0.937). The sample's SFGT completion times (mean ± SD) during the familiarization sessions were as follows: Familiarization session #1: 372.2 ± 48.3 seconds; Familiarization session #2: 361.1 ± 37.6 seconds; Familiarization session #3: 345.9 ± 41.1 seconds. For comparison, the trained firefighters' baseline SFGT time was 365.0 ± 56.4 seconds. To ensure familiarization with the SFGT, the first 2 SFGT sessions were performed in turnout gear (i.e., NFPA 1971: standard helmet, coat, pants, gloves, and boots). The final familiarization session was performed in turnout gear and required the use a self-contained breathing apparatus (SCBA; Scott Inc., Monroe, NC, USA). The total mass of the NFPA turnout gear and SCBA was 22.4 kg. To account for familiarization, the untrained firefighters performed the SFGT twice, on separate days, before the actual SFGT. The SFGT was identical for both trained and untrained firefighters.

The SFGT consisted of 7 events that simulate common tasks performed on the fire ground. Specifically, these tasks were selected with the assistance of the Fire Department's Training Officer and were identified as typical tasks performed by this Department. The SFGT tasks were performed consecutively in the following order without rest: stair climb, fire hose drag, equipment carry, ladder raise, forcible entry, and search and rescue. The order of these tasks was established based on the sequential order that these tasks are typically performed on the fire ground. The time required to complete each task was recorded. The stair climbing task consisted of ascending and descending a stair case of 13 steps 5 times while carrying 15.2 m of 3″ hose (mass = 22.2 kg) packaged as a high rise pack. During this task, the firefighters were allowed to touch the hand rails momentarily for stability purposes only. The firefighter began this task by standing next to the high rise pack, which was positioned on the ground at the base of the staircase. The time for this event began when the firefighter picked-up the high rise pack. The event was concluded (i.e., split time taken) when the high rise pack was placed on the ground after the fifth descent of the staircase.

The firefighter walked 14.6 m to the hose drag task. The hose drag consisted of pulling 45.7 m of 1¾″ (mass = 33.2 kg) uncharged fire hose with a nozzle. The firefighter was permitted to place up to 2.4 m of the fire hose over his shoulder or across his chest. The firefighter then walked or ran while dragging the hose 45.7 m with 1 90° turn around a barrel. The split was taken as the firefighter crossed the completion line.

The firefighter walked 14.6 m to the equipment carry task. The equipment carry task consisted of carrying 1 fire department issued saw (7.9 kg) and a set of irons (1 flat head axe and a Halogen bar; 6.6 kg) 70.0 m. There was a 180° turn at the midway point, such that the firefighter returned the equipment to the starting position. The split was taken when the equipment was placed on the ground.

The firefighter walked 48.2 m to the ladder raise task. The ladder raise consisted of raising a 7.3-m extension ladder from the ground to a building. The firefighter raised the tip of the ladder using a hand-over-hand technique to grasp each rung of the ladder until it rested against the side of the building. The split was taken as the firefighter released the ladder.

The firefighter walked 42.7 m to the forcible entry task. The forcible entry task was performed using a Keiser Force Machine chopping simulator (Keiser Inc., Fresno, CA, USA) and 4.1-kg sledge hammer. The firefighter placed both feet on the diamond plated surface and drove the 72.7-kg steel beam 1.5 m backward by striking the end of the beam with the sledge hammer. The split was taken when the opposite end of the beam crossed the back of the sled. The firefighter then placed the sledge hammer on the ground.

The firefighter walked 6.1 m to the search task. The search task was performed using a wooden tunnel-style attic space simulator with multiple obstacles designed to simulate A-frame style roofing trusses. First, the firefighter crawled through a tunnel (Dimensions: height = 0.60 m, width = 0.71 m, length = 2.40 m) and then made a 90° left turn into a second crawl space (Dimensions: height = 1.27 m, width = 1.20 m, length = 3.70 m) containing obstacles made from 2″ × 4″ boards, placed at various angles. The split was taken as the firefighter stood erect after exiting the attic simulator.

The firefighter walked 27.4 m to the rescue task. The rescue task consisted of dragging a 75.0-kg mannequin 22.9 m. The mannequin was wearing firefighter turnout pants. The firefighter positioned himself behind the mannequin, placed his hands around the mannequin's torso, and carried the mannequin backward. Firefighters were allowed to set the mannequin down and adjust their grip as needed during the task. The split and total SFGT time was taken as the mannequin's feet crossed the finish line.

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Performance Measures

Performance on the SFGT was evaluated in the trained and untrained firefighters by assessing the time to complete the SFGT tasks and mean relative heart rate. Relative heart rate was calculated by dividing the average absolute heart rate during the SFGT by the age-predicted maximum heart rate (i.e., 220 − age [years]) and multiplying the quotient by 100. In addition, in the trained firefighters, pre-SFGT and post-SFGT blood lactate level, and a global post-SFGT RPE were assessed. During the exercise session, heart rate and RPE were recorded immediately after the completion of each exercise, and a global RPE was reported after the completion of the workout.

The heart rate was recorded during the exercise session and during both SFGT conditions using telemetry. Specifically, a heart rate receiver and recording device (ActiTrainer, Fort Walton Beach, FL, USA) was placed in a neoprene sleeve on the firefighters' upper arm. The recording device reported the number of heart beats per 15-second sampling period. These data were downloaded to a computer using the manufacturer's software (ActiLife, Fort Walton Beach, FL, USA) and imported into a spreadsheet. Each 15-second set of myocardial contractions was multiplied by 4 to express the heart rate per minute. An average of these heart rates was calculated for the exercise session and during both SFGT conditions.

Blood lactate levels were assessed via a finger stick using a blood lactate monitor (Lactate Plus, Lactate.com, Waltham, MA, USA) with the firefighter in a seated position. The first drop of blood was wiped away. The second drop of blood was applied to an assay strip and inserted into the blood lactate analyzer. The calibration of the blood lactate analyzer was checked before testing each day with low and high control solutions. The accuracy of the blood lactate analyzer was within acceptable limits (i.e., low control solution: 1.0–1.6 mmol·L−1; high control solution: 4.0–5.4 mmol·L−1). This portable blood lactate analyzer has demonstrated high levels of validity (R2 = .99) and test-retest reliability (ICC = 0.99) at low, moderate, and high blood lactate levels (1). During the baseline SFGT session, blood lactate was measured before and 5 minutes after the SFGT. During the EX-SFGT session, blood lactate was measured before the exercise session, 5 minutes after the exercise session (i.e., ≈5 minutes before starting the SFGT), and 5 minutes after the completion of the SFGT.

Rating of perceived exertion was evaluated using a validated 0–11 category-ratio scale (3,15). Rating of perceived exertion was reported after each exercise during the training session and reported globally for the entire exercise session. Furthermore, RPE was reported globally after the completion of the SFGT during baseline and exercise conditions in the trained firefighters. The RPE was not reported in the untrained firefighters.

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Exercise Session

A circuit training exercise session was used in this study because it followed the trained firefighters' current exercise program. The exercise session required each firefighter to perform 5 resistance training exercises in rotational order. Two rotations of the circuit were completed such that each exercise was performed twice. The exercises included the seated cable row, barbell bench press, deadlift, dumbbell shoulder press, and prone plank. In most cases, the firefighter performed 10 repetitions of the externally resisted exercises using 95% of the ascertained 10RM load within a 30-second work interval. There were a few instances when the firefighter could not complete 10 repetitions with the 10RM load on the second set or the load was decreased slightly to allow for the completion of 10 repetitions during the second set. For the prone plank exercise, the firefighter maintained the isometric contraction during the 30-second work interval. In addition, a 3-minute treadmill walking bout was performed at 80.4 m·min−1 and 15% grade between the first and second rotations of resistance exercises. A 30-second recovery period was provided between all the exercises. A 1:1 work:rest ratio was used because it matched the trained firefighters' current training protocol. Rating of perceived exertion and heart rate were recorded after the completion of each exercise.

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Statistical Analyses

Descriptive statistics (mean ± SD) were used to describe the study sample and all outcome variables. Independent sample t-tests were used to compare the physical characteristics and predicted V[Combining Dot Above]O2peak between trained and untrained firefighters. Paired sample t-tests were used to evaluate the differences between the trained firefighters' baseline SFGT and exercise-SFGT conditions for time to completion, heart rate, and post-SFGT blood lactate levels. To describe the relative change in baseline SFGT vs. exercise-SFGT outcomes for trained firefighters, relative difference scores were calculated as follows: % difference = ([CT outcome − baseline outcome]/baseline outcome) × 100. The differences in RPE during the workout and the SFGT were not compared statistically because it violates assumptions of parametric statistics when evaluating categorical level data. Independent sample t-tests were used to compare the relative heart rate response of the SFGT in the untrained firefighters to the trained firefighters' baseline and exercise-SFGT conditions. Parametric statistics were not used to compare the SFGT time between the untrained vs. the trained firefighters' baseline and exercise conditions because 6 untrained firefighters were not physically able to complete the SFGT. As a result, their times could not be included to describe and evaluate the untrained group's SFGT time. Instead, descriptive comparisons were made between the untrained vs. trained firefighters' SFGT times. Cronbach's alpha was used to assess the reliability of the practice trials of the SFGT in the trained and untrained firefighters.

Effect sizes for the change in SFGT time, heart rate, and blood lactate were calculated as the absolute value of: ([meanbaseline − meanCT]/pooled SD). The observed power for all appropriate statistical analyses is provided. All dependent variables had normal distributions (i.e., |Fisher's coefficient of skewness < 1.96|) according to Fisher's coefficient of skewness (skewness/standard error of skewness). The level of significance was set at p ≤ 0.05 for all statistical analyses.

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Results

Relative heart rate and RPE responses for each exercise during circuit 1 and circuit 2 are displayed in Table 2. The relative heart rate and RPE responses were greater for each resistance training exercise (p ≤ 0.025) during circuit 2 compared with that during circuit 1, despite there being no difference in the external load used (p ≥ 0.191). The average relative heart rate throughout the CT exercise session was 66.5 ± 6.7% HRmax. The postexercise session blood lactate value was 9.78 ± 2.48 mmol·L−1.

Table 2

Table 2

Comparisons between the trained firefighters' baseline and exercise conditions for time-based outcomes on the SFGT are displayed in Table 3. The time to complete the SFGT was greater during the exercise condition compared with the baseline value (p = 0.002). Specifically, the time to complete the search and rescue tasks was greater during the exercise condition compared with the baseline value (p ≤ 0.024). There were no significant differences in times among the remaining 5 SFGT tasks (p ≥ 0.054).

Table 3

Table 3

The mean SFGT time for the untrained firefighters (n = 31) who completed the test was 422.5 ± 58.7 seconds. However, 6 additional firefighters were not able to complete the SFGT and therefore did not receive a completion time. Thus, the SFGT time sample distribution for all of the untrained firefighters (n = 37) can be expressed in quartiles as follows: 25th%ile = 514.5 seconds, 50th%ile = 429.0 seconds, 75th%ile = 390.0 seconds. Therefore, the mean exercise SFGT time (i.e., fatigued time = 399.9 seconds) of the trained firefighters was faster than approximately 70% of the untrained firefighters' baseline SFGT times. In addition, the mean baseline SFGT time of the trained firefighters was faster than 81% of the untrained firefighters.

Comparisons between the trained firefighters' baseline and exercise-SFGT conditions for physiological and RPE-based outcome variables (during the SFGT) are displayed in Table 4. In the trained firefighters, absolute and relative heart rate values during the SFGT were greater during the exercise condition compared with baseline (p ≤ 0.032) despite a greater ambient temperature during the baseline SFGT (20.7°C; CT-SFGT = 20.4°C; p = 0.039). On average, there was an increase in the post-SFGT RPE during the exercise condition compared with the baseline in the trained firefighters. There were no differences between resting or post-SFGT blood lactate levels between baseline or exercise conditions in the trained firefighters (p ≥ 0.771).

Table 4

Table 4

There was no difference in the relative heart rate response during the SFGT between the untrained firefighters' (90.1 ± 5.1% HRmax) and trained firefighters' baseline condition (88.7 ± 5.9% HRmax; p = 0.457; power = 0.125). Likewise, there was no difference in the relative heart rate response during the SFGT between the untrained firefighters' (90.1 ± 5.1% HRmax) baseline condition vs. the trained firefighters' exercise condition (91.2 ± 8.7% HRmax; p = 0.712; power = 0.077).

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Discussion

The primary purpose of this study was to determine the effect of exercise-induced fatigue on the simulated fire ground performance of firefighters. As hypothesized, exercise-induced fatigue was found to negatively affect the efficiency of performing a standardized SFGT. The 9.6% increase in SFGT time was likely because of a variety of peripheral and central factors that induced muscular fatigue. Detailed reviews describing the mechanisms of muscular fatigue may be found elsewhere (7). The findings from this study further emphasize that fire ground tasks are strenuous in nature and place significant stress on the nonoxidative and oxidative energy systems as evidenced by the elevated blood lactate and heart rate responses, respectively.

Evaluating the effect of fatigue among firefighters performing functional tasks is not novel. Smith et al. (18) evaluated the combined effects of heat exposure and physical fatigue on firefighter recruit performance by performing 3 repeated trials of standardized firefighting tasks. Unlike the results of this study, Smith et al. (18) found no significant differences between trial times, which may be partly because of a small sample size (N = 7). However, the recruits in Smith et al. (18) demonstrated a 6.6% increase in trial time between trials 2 and 3. Similarly, this study demonstrated a 9.6% increase in time to complete an SFGT between the baseline and exercise SFGT conditions.

Similar to this study, Smith et al. (18) also evaluated heart rate responses after the completion of 3 sets of firefighting tasks. The heart rates ranged from 93 to 100% (175–189 b·min−1) of the HRmax and did not statistically differ between trials. In contrast, the heart rate responses during this study increased significantly from 88 to 91% of HRmax from baseline to the exercise SFGT, respectively. The slightly greater heart rate responses reported by Smith et al. (18) may be because of a variety of factors, including the timing of the heart rate measurement (Smith et al. [18]: measured after the trial; this study: measured throughout the trial), differences in the physical demands of the firefighting tasks, disparities in hydration and fitness levels among the firefighters in each study, and the warmer ambient temperature (Smith et al. [18]: 47–61°C; this study: 21°C).

Rating of perceived exertion has been used as a subjective measure of work intensity among firefighters (18). Smith et al. (18) evaluated the RPE of firefighter recruits after the completion of 3 standardized trials of firefighting rescue tasks. The investigators reported that the RPE increased significantly from the first to the third trials (≈13 vs. 18 using 6–20 scale) (18). In this study, on average, the RPE was greater during the exercise SFGT compared with the baseline SFGT (9.5 vs. 8.2 using 0–11 scale; Table 4). Thus, both studies have demonstrated that performing repeated work or exercise bouts increased the perceived exertion of a standardized set of firefighting tasks.

In contrast to the methodological design used by Smith et al. (18), who evaluated the combined effects of heat exposure and physical fatigue on firefighter performance, Eglin and Tipton (5) conducted a study that evaluated the independent effect of heat exposure on the rescue performance of firefighter instructors. During this study, the instructors passively monitored firefighter students in a structure with an ambient temperature of 37°C for approximately 40 minutes but did not perform firefighting tasks. The instructors performed a baseline rescue task about 5 hours before heat exposure and a second time about 10 minutes after heat exposure. The results indicated no difference in rescue time or postrescue blood lactate levels, despite increases in the heart rate and RPE. There are several noteworthy comparisons to be made between the findings of Elgin et al. (5) and this study. First, the lack of a change in the firefighter rescue ability in Elgin et al. (5) may be attributed to less residual fatigue from the baseline rescue task. This seems plausible given that the baseline rescue test was performed approximately 5 hours before the post–heat exposure rescue test. In addition, the rescue task used in Elgin et al. (5) appeared to be less physically demanding from an anaerobic standpoint, compared with the SFGT used in this study. The relatively low posttest blood lactate levels reported by Elgin et al. (5) support this assertion. Both Elgin et al. (5) and this study did report significant increases in the heart rate and RPE from baseline to posttests. However, these increased cardiovascular and psychological responses may have occurred for different reasons. The heart rate and RPE responses of this study were likely elevated during the posttest because of the physical exertion of the exercise session. However, in the Elgin et al. (5) study, the increased heart rate was likely because of dehydration from the prior exposure to heat. Likewise the exposure to heat likely increased the postrescue RPE responses reported by Elgin et al. (5), because research has demonstrated that performing standardized tasks in the heat (40°C) increases perceived exertion compared with a cool environment (8°C) (11).

The NFPA encourages fire departments administrators to allocate on-duty time for firefighters to perform physical training (13,14). However, it is critical that we understand the benefits and limitations of employing on-duty physical training programs for firefighters. The findings from this study indicate that moderate intensity circuit training does reduce firefighter physical ability immediately after training. Some may perceive these findings to suggest that it is ill advised for firefighters to perform physical training while on duty. However, we recommend that fire service personnel and tactical strength and conditioning specialists consider the following implications regarding the use of on-duty physical training programs.

First, it should be noted that firefighter physical ability was evaluated immediately after the completion of an exercise session. We purposefully evaluated this “worst case scenario” in an effort to determine the magnitude of the decrement in firefighter physical ability. Additional research is necessary to determine the time course of exercise-induced fatigue on firefighter physical ability. At this point, it seems plausible to speculate that exercise intensity and the firefighter's fitness level will dictate the duration required to return to baseline physical ability levels. For example, a higher intensity exercise session (or higher intensity workload at the fire ground) and a lower firefighter fitness level would likely lengthen the postexercise or task recovery time. Furthermore, future research is needed to determine the effect of other types of training on the magnitude and time course of firefighter fatigue.

Second, the primary purpose of implementing an on-duty physical training program is to improve the firefighters' physical fitness levels. However, critics of on-duty physical training may argue that it more beneficial to not train while on duty, possibly because of the acute effects of fatigue on firefighter physical ability. We contend that maintaining higher levels of physical fitness, in part, through on-duty physical training, appears to compensate for the effects of exercise-induced fatigue. Our data support this contention. That is, when comparing the exercise SFGT time (i.e., fatigued condition) of the trained firefighters to the baseline (nonfatigued condition) SFGT time of untrained firefighters, the trained firefighters performed more efficiently than approximately 70% of the untrained firefighters. From a physical ability perspective, this example indicates that the benefits of regular on-duty physical training may outweigh the decrease in firefighter physical ability.

Third, critics of on-duty physical training programs for firefighters may suggest that firefighters should exercise during their off-duty time. Although, this strategy may provide certain benefits, because it would likely avoid the acute effects of fatigue, it may introduce a new set of limitations to firefighter physical ability, such as delayed onset of muscle soreness (DOMS). The DOMS has also been shown to decrease muscular strength for a brief period of time after training (17). Furthermore, similar to the low prevalence of leisure time physical activity performed by the general public (16), it is likely that many firefighters would not participate in a voluntary off-duty physical training program.

Fourth, to further demonstrate the justification for the use of on-duty physical training programs for firefighters, one must consider the potential of these programs to address 2 major health concerns among firefighters, namely, cardiovascular disease and acute musculoskeletal injuries. There are strong data to support the association between physical fitness level and risk of cardiovascular disease (6); however, there are limited data in firefighters demonstrating that physical training reduces the prevalence of acute injuries. Nonetheless, one such study in firefighters reported a decrease in the number of back, knee, and ankle injuries because of a physical training program (12).

Fifth, the implications of this study further highlight the importance for fire department administrators and tactical strength and conditioning professionals to consider the most appropriate time to schedule on-duty physical training. That is, given these findings, it may be advisable to schedule on-duty physical training during low-volume emergency call times or just before the completion of the firefighters' shift.

It should be noted that there were several limitations of this study. For instance, caffeine and dietary intake, and hydration status were not controlled. These factors may have impacted performance on the SFGT and the accompanying heart rate response. In addition, it is unknown whether the validity of the V[Combining Dot Above]O2peak prediction equation (20) used on the Gerkin treadmill protocol differs between trained and untrained firefighters, because this prediction equation was applied to both groups in this study.

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Practical Applications

The results from this study indicate that the occupational efficiency of firefighters may decrease as a result of performing exercise while on duty. However, the long-term benefits of on-duty physical training (e.g., improved work tolerance, decreased risk of heart disease) may outweigh the acute decrements in firefighter performance. Fire department administrators may consider scheduling on-duty physical training during low volume emergency call times or just before the completion of a shift to minimize the likelihood of responding to an emergency during an exercise session. Furthermore, this study demonstrated that firefighters who train regularly and possess higher fitness levels tend to perform job-specific tasks more efficiently than do untrained and lesser fit firefighters. This study further emphasizes the importance of implementing an exercise program for firefighters.

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Acknowledgments

The authors would like to thank the Kentucky Fire Commission for their financial support of this project. In addition, they are grateful to Chief Gerald Tatum and the firefighters for participating in this study. Finally, they would like to thank the individuals who assisted in collecting data for this project, especially, Phillip Lloyd and Jordon Macht. The results of this study do not constitute endorsement of any product by the authors or by the National Strength and Conditioning Association.

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Keywords:

circuit training; exercise; occupation; resistance; tactical

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