Introduction
The physical demands of firefighting, as an occupation, are characterized by significant activation of the cardiovascular, metabolic, and hormonal systems. Heart rates in excess of 95% of maximum (14,15,22,24,29,30), rates of oxygen consumption approaching o2max (4,11,29,30), and significant activation of the sympathoadrenal axis (18,26) have been recorded during firefighting, demonstrating the significant physiological stresses that occur during these tasks. Previous studies on firefighters have assessed factors most closely aligned with steady state activity, that is, aerobic metabolism (4,8,9,20,24,29), whereas little is known about the role of anaerobic energy sources during firefighting tasks (30). Furthermore, the physical attributes and fitness components required for optimal firefighting performance have not been fully identified. Based on these limitations, it has been difficult to design appropriate remedial intervention programs that make optimal improvements in the qualities most important for firefighting performance.
Several studies have correlated physical attributes with performance in individual firefighting-related tasks (6,19,29,31). In these studies, muscle strength (19,29,31), body composition (31), absolute o2max (29), and muscle endurance (19,31) are significantly related to task performance. Despite several studies that have demonstrated high rates of oxygen consumption (3,4,11,13,16,30), results examining the relationship between firefighting performance field tests and cardiovascular fitness are equivocal (19,31).
Because the oxygen demands of firefighting can exceed 40 ml·kg−1·min−1 (3,4,11,13,16,30), intense muscular exertions in firefighters with compromised cardiovascular systems can precipitate cardiac events when the heart's demand for oxygen (myocardial oxygen demand) exceeds its oxygen supply capabilities. The product of heart rate (HR) and systolic blood pressure (rate pressure product [RPP]) offers a reliable index of myocardial oxygen demand and serves as an indicator of the cardiovascular and metabolic stress placed on the heart during strenuous activity. Reducing the RPP response may reduce the risk of a cardiac event in predisposed firefighters by lowering the cardiovascular and metabolic stress on the heart during the task. However, no information is available on the fitness and body composition components that are most closely associated with a low RPP response to firefighting tasks.
Although most studies have examined the dynamics of HR and oxygen uptake during firefighting performance, some have observed substantial elevations in peak lactate values (11,29), and varying oxygen demands (11), elevated respiratory-exchange ratios (RER) (30), and HRs (8,21) among different tasks. Coupled with the inherently unpredictable nature of emergency situations, the data suggest that firefighting is an intermittent, nonsteady state activity. Despite the apparent importance of anaerobic fitness, limited research has been done to clarify the relationship between muscular power and firefighting performance. One study examined the importance of muscular power, as measured by the standing long jump, to firefighting tasks (6). More recently, another study found a moderate relationship between peak power during the Wingate anaerobic cycling test (WAnT) and firefighting performance (30). Anaerobic endurance, as measured by the 400-m run, was also reported to be positively related to firefighting task performance (19). Thus, there is a need to clarify the relative influence of aerobic vs. anaerobic fitness to firefighting performance.
In this context, few studies have examined the relationship between different fitness types and integrated firefighting tasks. The Candidate Physical Ability Test (CPAT), a nationally established firefighting simulation test often used to screen applicants, is one such integrated task. The physiological demands of CPAT have only recently begun to be assessed, during which RERs <1.0 were observed (30), suggesting significant activation of anaerobic metabolism. Moreover, absolute o2max during treadmill running was able to explain 57% of the variation in CPAT performance. However, firefighters were not studied, order and fatigue effects were not controlled, body composition was not measured, and only indirect assessments of muscular strength were performed. Information is also lacking on the relative contribution of the various physical or functional attributes that determine optimal performance on the CPAT, because this information could improve the application screening process by establishing minimal physical capacities necessary to complete CPAT successfully.
Therefore, the purpose of this study is to examine the relative importance of several physiological variables during CPAT performance in active firefighters, using a standardized, multiday testing protocol. Because of the intermittent nature of fighting fires, it was hypothesized that physical attributes, such as muscular strength, power, and anaerobic power are better predictors of CPAT performance than aerobic capacity.
Methods
Experimental Approach to the Problem
Firefighting is characterized by significant activation of aerobic and anaerobic metabolism. Several physical attributes have been associated with firefighting performance, but the results are inconsistent and limitations exist within the literature. To address these issues, we assessed physical attributes previously found to be associated with firefighting performance using active firefighters. Candidate Physical Ability Test was used as a simulation of firefighting performance. By assessing a wide array of physical attributes in subjects who are familiar with these tasks, we sought to determine which physical attributes best account for variance in CPAT performance, and the minimal fitness requirements necessary to pass CPAT. Values for each physiological variable were calculated and compared between those who passed and those who failed CPAT. Correlations were calculated for the relationship of the independent variables (physiological attributes) and CPAT performance (dependent variable). Information from these relationships was then used to estimate their relative contributions to successful firefighting performance.
Subjects
Thirty-three volunteer and career firefighters, aged 18-45, from the Baltimore-Washington metropolitan area fire departments volunteered to participate in a 5-day testing battery. Subjects were actively recruited by the Maryland Fire and Rescue Institute (MFRI) through the use of flyers, Internet advertising on the MFRI website, and in-person recruitment visits to local fire departments. After the methods and procedures of the study were explained, all subjects signed a written consent form approved by the Institutional Review Board (IRB) of the University of Maryland, College Park. The IRB approval for all procedures used during the study was granted before any testing. The exercise training status of the subjects was representative of the fire departments from which they were recruited. Most were not undergoing a formal training program, but some were. Many of those who were not highly trained were physically active, whereas others were relatively inactive. No subjects had more than 2 risk factors for cardiovascular disease as determined by guidelines set forth by the American College of Sports Medicine (1).
Subject characteristics for men and women, both combined and separated, are presented in Table 1. Men were significantly taller (p = 0.001) and heavier (p = 0.003) than women, but there were no significant differences in percent body fat (p = 0.506).
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Table 1: Physical characteristics of male and female firefighters.*â€
Procedures
To determine the physical characteristics of the subjects, the following physical assessments were performed. A minimum of 1 day of rest separated each day of testing to minimize fatigue. No more than 2 weeks passed between successive tests to minimize any changes in fitness between testing dates. The order of testing is presented in Figure 1.
Figure 1: Multiday standardized testing order for all subjects.
One Repetition Maximum
Air-powered resistance training machines (leg extension machine, chest press machine, leg press machine, Keiser Sports/Health Equip. Co., Inc., Fresno, CA, USA) were used to perform all 1RM tests. Strength testing was performed bilaterally on the chest and leg press and unilaterally on the knee extension exercise as described in detail by Delmonico et al. (7). For all strength tests, subjects were familiarized to the testing equipment between 2 and 5 days before testing to help control for the effects of motor learning on 1RM performance. The familiarization consisted of 4 sets at varying percentages of the estimated 1RM based on body weight. The first set was performed for 10 repetitions with no resistance and subsequent sets of 8 repetitions at 10% of estimated 1RM, 5 repetitions at 30% of estimated 1RM, and 3 repetitions at 50% of the estimated 1RM were performed. Estimated chest press 1RM was 75% of body weight, knee extension was equal to bodyweight, and leg press was equal to 3 times the bodyweight.
For all strength tests, subjects completed 2 minutes of seated cycling as a warm-up. Testing proceeded with single repetition sets and 1-minute rest between each set. The resistance increased in a manner that allowed for the determination of 1RM within 8-10 trials. For the leg press, the subjects were seated on the machine with the seat positioned so that the knee joint forms a 90° angle. They were instructed to place their arms across their chest and breathe normally. A successful repetition was counted when the knee was fully extended. For the chest press, subjects were seated in a position that aligned the handlebars with the xyphoid process. Subjects were instructed to keep the head and back against the back pad and their feet flat on the floor. A successful repetition was achieved when the elbows were fully extended. For the knee extension exercise, each leg was tested separately, with the right leg tested first. The seat was positioned so that the axis of rotation of the knee joint lined up with the axis of rotation of the knee extension machine. Subjects were instructed to cross their hands across their chest and breathe normally. A restraint was placed across the subject's lap to restrict movement of the hips. A successful repetition was achieved when the knee joint angle exceeded 165°, as assessed by an indicator light when this angle was reached.
Subjects also performed maximum isometric fingertip force production tasks. They were asked to produce maximum isometric force with all 4 fingers in flexion over a 3-second interval while watching the force feedback of the task finger(s) on the computer screen (23). Signals from the force sensors were conditioned, amplified, and digitized at 1,000 Hz with a 16-bit A/D board (PCI 6034E, National Instruments Corp., Rockville, MD, USA) and a custom software program made in LabVIEW (LabVIEW 7.1, National Instruments Corp.). The peak magnitudes of the individual finger forces and the 4-finger force were used to determine finger strength.
Muscle Endurance
The Keiser A-300 Chest Press machine and Leg Press machine were used to test muscle endurance. A maximal repetition test against a predetermined percentage of strength was used to determine muscular endurance, as endorsed by American College of Sports Medicine as a valid measure of muscular endurance (2).
Muscle endurance in the chest press and leg press exercises was assessed directly after the achievement of a 1RM in the respective movement. A 5-minute rest period was taken after the final trial of the 1RM testing process. The same seat position was used for both 1RM and muscle endurance testing. Subjects completed as many repetitions as possible with 80 and 70% of the 1RM in the leg press and chest press, respectively. They were instructed to breathe normally, ensure a full range of motion, and to move continuously. Pausing between repetitions resulted in the termination of the test. The total number of repetitions was recorded.
Muscle Power
An air-powered resistance training machine (Keiser A-300 Leg Extension machine, Keiser Sports/Health Equip. Co., Inc., Fresno, CA, USA) was used to test for muscle power, as described previously (7). Briefly, after completing a 5-minute cycling warm-up, subjects performed 3 power tests on each leg alternating between right and left at 50, 60, and 70% of their knee extension 1RM, with 30 seconds of rest between each of the 3 trials and 2 minutes of rest between each increase in resistance. The peak value was obtained within each individual trial. To determine the overall peak power for each load, the highest value among the 3 trials was selected. Test results were recorded using a software program from Keiser Sports/Health Equipment Co. Muscle power was tested on 2 separate occasions, with approximately 3-5 days in between. The higher of the 2 values was used, because this value would represent peak power. Muscle power testing was shown to be both reliable and valid in a previous study using similar equipment, with an intraclass correlation coefficient of 0.91 (5).
Peak Anaerobic Power, Mean Anaerobic Power, and Fatigue Index
The WAnT was administered using a cycle ergometer (Monark 824E, Varberg, Sweden) to determine a fatigue index, maximal anaerobic power, and mean anaerobic power. Subjects initially pedaled with no resistance for 3 minutes, followed by 2 5-second practice sprints separated by approximately 30 seconds of active recovery with no resistance. The subjects rested passively for 2 minutes before completing a 30-second, maximal WAnT test against a resistance equivalent to 7.5% of bodyweight. The number of revolutions completed in each 5-second period was recorded over the course of the 30-second test.
Aerobic Capacity
A graded treadmill exercise protocol was used to determine o2max. The treadmill speed was initially set to a speed that elicited an HR equivalent to 85% of age-predicted maximal HR and remained constant throughout the test. After appropriate warm-up, the treadmill speed was increased to the predetermined testing speed. The grade of the treadmill started at 0% incline and was increased by 2% every 2 minutes thereafter until volitional fatigue was achieved. The HR was recorded every 2 minutes. The highest oxygen uptake recorded was considered to be o2max. A test was considered valid if an RER in excess of 1.10 or an HR in excess of age-predicted maximum was recorded.
Body Composition
Body composition was assessed through the use of dual-energy x-ray absorptiometry (DEXA) scanning using fan beam technology (model QDR 4500A, Hologic, Waltham, MA, USA), as previously described (7). The coefficients of variation were 0.6% for fat-free mass (FFM) and 1.0% for percent fat. As a measure of criterion-referenced validity, FFM as measured by DEXA was significantly correlated to FFM measured with computer topography (R2 = 0.98) (28). The DEXA scanner was calibrated daily before use. The subjects were measured for height and weight to the nearest 0.1 cm and 0.1 kg before scanning.
Cardiovascular Responses to Stair Climbing
The cardiovascular responses to stair climbing were determined through the use of a Stairmaster® step mill (7000PT Step mill Stepper, Stairmaster, Vancouver, WA, USA) and an automated blood pressure monitor (Tango+, SunTech Medical, Inc., Morrisville, NC, USA). Before testing, 3 electrodes were placed on the subject's chest at V2, V6, and the right limb ground position. Subjects wore a 22.7-kg weight vest and completed a 2-minute warm-up on the step mill at a rate of 45 steps per minute. They then rested passively for 3 minutes before blood pressure assessment. An additional 11.3-kg weight vest was placed on the subject's shoulders, for a combined weight of 34.0 kg, and the test began with an additional 30-second warm-up at 45 steps per minute. After 30 seconds, the step rate was increased to 60 steps per minute, where it remained for 3 minutes. The HR was recorded as the step mill increased to 60 steps per minute and was recorded every 30 seconds thereafter. Automatic blood pressures were taken at 1, 2, and 3 minutes into the testing protocol. The stair climbing was performed with the same parameters as the stair-climb portion of the CPAT.
Candidate Physical Ability Test
The CPAT consists of 8 firefighting specific tasks separated by a 25.9-m walk and performed while wearing a 22.7-kg load simulating the Self-Contained Breathing Apparatus used by firefighters during live fire events. Subjects were required to walk during this interval. Subjects were timed for the duration of each task and during each transition using standardized procedures for all 8 tasks as described by the Fire Service Joint Labor Management Wellness/Fitness Initiative of the International Association of Firefighters and International Association of Fire Chiefs. The sum of each task and transition constituted the cumulative time, measured in seconds. A passing score is a cumulative performance time ≤10 minutes and 20 seconds. No testing was performed before CPAT or on the day before performing CPAT.
The first task was the stair climb. The subject wore an additional 11.3-kg weight vest. The subject warmed up at a rate of 50 steps per minute for 20 seconds. At the end of the 20-second period, the test commenced and the subject climbed at a rate of 60 steps per minute for 3 minutes. The task was concluded upon dismounting the step mill and the removal of the additional weight.
The second task (hose drag) consisted of dragging a 61.0-m fire hose 22.9 m, executing a 90° turn, then dragging the hose a further 7.6 m. The subject then dropped to 1 knee and pulled in 15.2 m of hose.
The third task (equipment carry) consisted of removing 2 saws from a shelf, 1 at a time, and placing them on the ground. The subject then picked up and carried the 2 saws for 75 ft, circled a drum, and returned to the starting point. The saws were placed on the ground, picked up one at a time, and placed back on the shelf.
For the fourth task (ladder raise and extension), the subject lifted the unhinged end of a 7.3-m ladder and raised it in a hand-over-hand motion until it rested vertically on the wall. The subject then raised and lowered the fly section of a 7.3-m ladder by pulling on a rope in a hand-over-hand motion. The task started when the subject made contact with the first ladder and ended with the release of the rope of the second ladder.
The fifth task (forcible entry) began when the subject picks up a sledgehammer. The subject swung the sledgehammer at a wall, depressing a metal box until the buzzer was activated. The task concluded when the subject released the sledgehammer after activating the buzzer.
The sixth task (search) consisted of crawling through a 0.9 m high, 1.2 m wide, and 19.5-m-long tunnel maze with 2 separate 90° turns. Within the maze are obstacles. The task began when the subject placed a hand or knee on the ground while preparing to enter the maze. The task is completed upon returning to 2 ft after exiting the maze.
During the seventh task (rescue), the subject dragged a 61.2-kg mannequin by attached handles for 10.7 m, executed a 180° turn around a drum, and returned 10.7 m to the starting position. The task began when the subject first made contact with the mannequin and ended with the release of the mannequin after dragging the mannequin across the starting line.
The eighth task (ceiling breach and pull) began when the subject stepped inside the metallic structure. The subject used a pike pole to raise a weighted, hinged door 3 times. The subject then used the pike pole to pull down on a second hinged door for 5 repetitions. This process is repeated 3 more times for a total of 4 rounds. The task concluded when the subject stepped outside of the structure.
Statistical Analyses
Means and SEs were calculated for all variables. To determine which variables were related to passing and failing the CPAT, subjects were placed into 2 groups, those with passing CPAT times (N = 18; ≤10 minutes and 20 seconds) and those with nonpassing times (N = 15; >10 minutes and 20 seconds). Mean values for each physiological variable were calculated by group. These means were compared using T-tests for independent means to determine which variables distinguished successful CPAT performers from nonsuccessful performers. Individuals who failed to complete CPAT were considered nonsuccessful performers. T-tests for 2 independent means were performed to determine significant differences between groups. Pearson product-moment correlation coefficients were also calculated to determine correlations between the physiological attributes described above (independent variables) and CPAT performance (dependent variable). Correlations between these independent variables and RPP were also calculated in the same manner. To minimize the chances of a type 1 error because of multiple correlations, p values were set at 0.01 for all correlations. Individuals unable to complete CPAT were not included in correlation analyses.
The combination of physiological characteristics that best predict CPAT performance was determined by stepwise linear regression analysis. Likewise, this analysis was also used to determine the physiological attributes that best predict performance in the individual CPAT tasks. The resulting equation that predicted the largest portion of the variance was then selected. When significant correlations were present for RPP relationships, stepwise linear regression was again used to determine the most significant predictors. Individuals unable to complete CPAT were not included in the regression analyses. P values were set at 0.05 for the overall regression models.
Results
Muscle Strength, Muscle Power, o2max, and Wingate Anaerobic Cycling Test
Table 2 shows muscle strength, muscle power, o2max, and WAnT for men and women. As expected, men demonstrated significantly higher muscular strength in chest press (p < 0.001), leg press (p < 0.001), and knee extension (p < 0.001) exercises than did women. Men also exhibited significantly higher peak power (p < 0.001) and mean power (p < 0.001) during WAnT and absolute o2max (p = 0.003). However, when standardized to body weight, there were no significant differences in o2max (p = 0.454) and peak power during WAnT (p = 0.101), whereas differences in mean power approached significance in favor of the men (p = 0.020).
Table 2: Strength and power characteristics and CPAT performance of male and female firefighters.*â€
Determinants of Successful Candidate Physical Ability Test Performance
When subjects were grouped based on successful vs. unsuccessful CPAT performance, between group differences in WAnT and o2max were observed, in both absolute terms and relative to bodyweight. Differences in peak power expressed in absolute terms during WAnT were right on the borderline for being significant (p = 0.011, Figure 2A). However, relative peak power was 22% higher in those who successfully completed CPAT (p < 0.001, Figure 2B). Mean power during WAnT was 45% higher in those who completed CPAT with a passing score, as compared to those who did not (p < 0.001, Figure 2C). Mean power expressed relative to bodyweight was 25% higher in successful CPAT performers (p < 0.001, Figure 2D). Additionally, absolute o2max was 23% higher in firefighters who successfully completed CPAT (p < 0.001, Figure 3A). When o2max was expressed relative to body weight, differences between groups were slightly attenuated (17%), but still significant (p < 0.01, Figure 3B). There was a trend toward differences in the response to stair climbing between the successful and unsuccessful CPAT performances for peak HR in response to stair climbing (p = 0.015, Figure 3C) and the percentage of maximal HR achieved during stair climbing (p = 0.013, Figure 3D). Finally, upper and lower body strength and percent body fat were not significantly different between successful and nonsuccessful CPAT performers; however, greater upper body strength (p = 0.038) and lower percent body fat (p = 0.029) trends favored those with faster CPAT times.
Figure 2: A) Peak power, B) relative peak power, C) mean power, D) relative mean power during the Wingate anaerobic cycling test (WAnT) in those who pass (≤10 minutes and 20 seconds) vs. those who fail (>10 minutes and 20 seconds) the candidate physical ability test (CPAT). *Values are significantly different from those who fail the CPAT (p < 0.01).
Figure 3: A) Absolute
O
2max (L·min
−1), B) relative
O
2max (ml·kg
−1·min
−1), C) heart rate (b·min
−1) at the conclusion of stair mill task, and D) percentage of maximal heart rate achieved during stair mill task in those who pass (≤10 minutes and 20 seconds) vs. those who fail (>10 minutes and 20 seconds) the CPAT. *Values are significantly different than in those who fail the CPAT (
p < 0.01).
Relationship between Physical Attributes and Candidate Physical Ability Test Performance Time
The relationships between each physical attribute (i.e., o2max, WAnT performance, muscle strength, muscle power, body composition, and cardiovascular response to stair climbing) and CPAT performance time were assessed using Pearson correlation coefficients. The results are presented in Table 3. The variable with the strongest correlation with CPAT performance was mean power during WAnT (r = −0.66; p < 0.001). This relationship remained significant when mean power was normalized for body mass (r = −0.598; p < 0.001). In addition, fatigue index during WAnT (r = 0.559; p < 0.001) was significantly related to CPAT performance. Absolute o2max (r = −0.602; p < 0.001), 4-finger isometric grip strength (r = −0.504; p = 0.009), and upper body strength (r = −0.485; p < 0.001) were also significantly related to CPAT performance. Furthermore, maximal HR response to stair climbing was significantly related to performance time (r = 0.523; p < 0.01), and percent of maximal HR achieved during the stair climb approached significance (r = 0.488; p = 0.012). In contrast, lower body strength (p = 0.044) and percent body fat (p = 0.104) were not significantly related to CPAT performance.
Table 3: Correlations between physical attributes and CPAT time.*
The results of the linear regression analysis determined that absolute o2max and fatigue index during WAnT combined best predicted CPAT performance time (Adj. R2 = 0.817; p < 0.001). Their combined predictive power was significantly higher than their individual contributions.
Determinants of Rate Pressure Product
Contrary to our hypothesis, neither o2max (p = 0.378), body composition (p = 0.340), nor lower body strength (p = 0.940) were significantly related to RPP.
Individual Task Determinants
Separate models were constructed for each of the individual CPAT tasks, and results are presented in Table 4. Because not all subjects completed all aspects of testing, some regression equations contain <33 subjects. All models were significant (p < 0.05) with the exception of the model for ceiling breach and pull. The R2 values ranged from 0.25 to 0.73. Similar to the findings with regression models for total CPAT time, measures of cardiovascular and anaerobic fitness were the best predictors of individual task performance. The combination of mean power during the WAnT and HR at the conclusion of the stair climbing task best predicted performance time during the hose drag (R2 = 0.61; p = 0.0001). Performance during the ladder raise and extension was related primarily to mean power during WAnT and the percentage of maximum HR achieved during stair climbing (R2 = 0.68; p < 0.0001). Forcible entry performance was best associated with the combination of sex and mean power during WAnT (R2 = 0.73; p < 0.0001). The combination of mean power during WAnT, height, and diastolic blood pressure at the conclusion of stair climbing best predicted performance during the search tasks (R2 = 0.65; p = 0.0002).
Table 4: Regression coefficients for individual CPAT tasks.*
Discussion
The results of this study describe, for the first time, the relative contributions of anaerobic fitness, maximal oxygen uptake, muscular strength, percent body fat, and the cardiovascular responses during stair climbing to CPAT performance. It is also the first report to assess the physiological determinants of individual tasks during the CPAT. The data indicate that absolute o2max and anaerobic fatigue resistance combined significantly predict a substantial portion of the variance (82%) in CPAT performance. This finding complements and extends the recent work by Williams-Bell et al. (30) who observed o2 values in excess of 38 ml·kg−1·min−1, HR > 165 b·min−1, and RER > 1.0 for individual firefighting tasks, indicating high levels of both aerobic and anaerobic metabolism. Nevertheless, our hypothesis that anaerobic fitness and muscular strength would serve as a strong predictor of firefighting performance was only partially supported by our results. Although upper body strength was a significant predictor of CPAT performance, neither upper nor lower body strength met our criterion (p < 0.01) for being a significant predictor of CPAT success (i.e., pass vs. fail). Moreover, our specific hypothesis that anaerobic fitness would serve as a better predictor of performance than aerobic capacity was not supported by our data. Regression equations describing the physiological attributes as determinants of individual CPAT tasks were significant for all tasks, except the ceiling breach and pull. However, no relationship was observed between RPP during stair climbing and any of the assessed physical attributes.
Our finding that absolute o2max is significantly related to firefighting performance was supported by von Heimburg et al. (29), who found that absolute, and not relative o2max, was the best predictor of firefighting tasks. Additionally, absolute o2max was recently shown to be the best predictor of CPAT performance (30). These findings argue for the importance of possessing a large metabolic capacity. Prior research has demonstrated oxygen uptakes approaching or in excess of 40 ml·kg−1·min−1 during simulated firefighting tasks, indicating a high oxygen requirement during firefighting (3,4,11,13,16,30). A large absolute o2max may allow the firefighter to meet these energy demands without significant activation of anaerobic metabolic pathways, delaying the accumulation of high muscle and blood lactate, thereby delaying fatigue. The relationship between absolute o2max and CPAT performance could indicate the importance of body size to performance, given that successful completion of CPAT may require high absolute levels of aerobic fitness and strength. Interestingly, body mass was not found to be related to performance in this study.
Although aerobic fitness appears to play a role in CPAT and firefighting performance, little information exists regarding the anaerobic contributions. It has been shown that anaerobic metabolism contributes ∼30 to 40% of energy demands during simulated firefighting tasks (4) and these tasks are also associated with elevated lactate levels (11,17,25,29). As hypothesized, our results demonstrated that measures of peak and mean anaerobic power were highly related to CPAT performance. We are aware of only 2 other reports that have addressed this relationship (19,30), with only 1 using the CPAT as a surrogate to firefighting performance (30). Rhea et al. (19) determined that 400-m run time was significantly related to the cumulative time taken to complete 5 separately firefighting tasks (r = 0.79) and Williams-Bell et al. (30) found no difference in fatigue resistance during WAnT. Despite the equivocal nature of prior research, our data support the importance of anaerobic metabolic contributions during firefighting tasks.
Our finding that anaerobic fatigue resistance and absolute o2max combined best predicted CPAT and contributes to such a large portion of the total variance in CPAT performance (82%) is novel. Although absolute o2max has previously been shown to be independently related to CPAT performance, the relationship of CPAT to anaerobic fatigue resistance has been less clear (19,30). However, both oxygen-dependent (3,4,11,13,16) and oxygen-independent systems (4,11,17,25,29) appear to be activated during firefighting tasks and these metabolic systems are thought to be the best independent predictors of firefighting performance (19,29,31). Hence, when we combined the 2 variables, their predictive power is greatly increased and explains over 80% of the variance in CPAT performance time.
Although research does support a role for anaerobic fitness during firefighting, prior research failed to find any relationships between anaerobic fitness and CPAT (30). This could be the result of differences in methodology and purpose. The present study used active professional and volunteer firefighters to determine which physiological attributes best predict CPAT performance, whereas Williams-Bell et al. (30) used volunteers with no prior firefighting experience to determine the physiological demands of CPAT. Our intent was to minimize the influence of skill acquisition as a potential confounding variable by using firefighters familiar with all the tasks comprised in the CPAT. We also attempted to control for fatigue effects by separating tests that could impair performance on subsequent tests. Considering that o2max, muscular strength, and endurance testing all preceded the WAnT during the single day testing (30), this may account for the lack of an association with anaerobic fitness and CPAT in previous studies.
Predicted leg press strength has recently been shown to be related to CPAT performance (30). However, lower body strength was not significantly different between successful and nonsuccessful CPAT performers in the present study. Similarly, Rhea et al. (19) and von Heimburg et al. (29) found no relationship between quadriceps strength and firefighting performance. In contrast, upper body strength and firefighting performance appear to have a more consistent relationship, as the trend we observed for upper body strength differences between successful and unsuccessful completion of CPAT is supported by previous research showing that bench press (19,29) and pull-up (31) performance were also significantly related to firefighting performance. More recently, bench press performance was also found to be positively correlated with CPAT performance (30). Thus, it appears that although upper body strength is critical to firefighting performance, lower body strength does not appear to be as important.
In another measure of basic strength, a significant positive relationship between grip strength and firefighting performance has previously been established (6,19,30,31). Our results confirm the importance of isometric grip strength to firefighting performance. Hand strength may influence firefighting performance because of the repeated gripping which is required to successfully complete individual tasks. Additionally, a strength index composed of leg, neck, and chest press was found to be higher in faster performers during a simulated firefighting rescue (29).
Percent body fat was not significantly related to CPAT performance, although trends toward significance were evident in this study. These findings were supported by some investigators (19) but not by others (6,31). The studies that established a relationship between percent body fat and performance employed skinfold measurements, whereas those that do not support this used more direct assessments of body composition, that is, DEXA and air plethysmography, respectively. These differences may account for the conflicting findings and calls into question the importance of body composition during CPAT.
The maximal HR response to a stair climbing task was significantly and negatively related to CPAT performance in this study. This may represent the advantage of starting the remainder of the CPAT at a lower percent of maximal HR. A greater HR response to stair climbing may also indicate greater levels of cardiovascular activation during a standardized task and thus a lower fitness level. However, RPP response to stair climbing was not significantly related to CPAT performance, suggesting that myocardial oxygen consumption during this task is not related to overall CPAT performance. Contrary to our hypothesis, the RPP response to a stair climbing task was not significantly related to any measured physiological attributes.
Although the cardiovascular and metabolic response to individual tasks during CPAT has been investigated (30), to our knowledge, this study is the first report on the physiological determinants of individual tasks during CPAT performance. The results of regression analyses determined significant prediction equations for all individual tasks except the ceiling breach and pull. Similar to our finding that anaerobic resistance to fatigue and absolute o2max best predict CPAT performance, measures of aerobic and anaerobic fitness best predicted individual task performance, including the hose drag, ladder raise and extension, forcible entry, and search tasks. Explanations for these relationships are beyond the scope of this study, but as all tasks are performed under the influence of cumulative fatigue, it appears the ability to sustain a high metabolic output with enough reserve for short bursts of exertion is critical for individual task performance.
The HR response to exercise can be influenced by many different factors in addition to the training status of the participant. These include, but are not limited to, caffeine usage (12), medications (10), and shift work. Because many of the subjects in the present study were shift workers, the latter may be especially important, as shift work has been shown to affect both blood pressure and HR dynamics (27).
There were several limitations in this study. The relatively small sample size of nonrandomly selected subjects may have limited the scope of the population for which the results can be generalized. Additionally, the low number of female subjects limited our ability to make accurate and reliable determinations of sex differences in our results. Future investigations should study larger groups of women to confirm whether the physiological attributes in this study tend to influence CPAT performance differently in women. We would also recommend that future investigations address the relationship of shift work, HR variability, and the extent to which shift work influences occupational stress. Lastly, because of the cross-sectional design of the present study, we are unable to determine causal or independent relationships between specific physical attributes and CPAT performance. Future research should seek to establish independent effects by using interventions, such as exercise training programs and control groups to isolate changes in independent physiological attributes and to control for other intervening factors that could influence CPAT performance.
In conclusion, this study demonstrated that anaerobic resistance to fatigue and aerobic capacity combined are important physiological attributes for successful firefighting performance, accounting for over 80% of the variance in CPAT performance. Similarly, performance in the majority of individual tasks appears to be best predicted by surrogates of aerobic and anaerobic metabolism. Based upon the results of the present study, improving aerobic capacity and anaerobic fatigue resistance should be a major focus of remedial programs designed to improve firefighting performance.
Practical Applications
The results of this study indicate the important contributions of both aerobic and anaerobic fitness to successful CPAT performance. As aerobic capacity and anaerobic resistance to fatigue account for over 80% of the variability observed in CPAT performance, the fitness professional working with firefighters should target these 2 specific attributes when creating training programs aimed at improving CPAT performance in particular, and firefighting performance in general. This study also provides basic information to be used by fire departments to effectively screen potential candidates with simple fitness field tests to identify potential recruits who may lack the necessary fitness prerequisites to pass CPAT. Furthermore, the results of this study provide further support that active firefighters lacking minimal aerobic and anaerobic fitness levels may not be prepared for the required duties of the firefighting profession duty.
Acknowledgments
This study was supported by research grant # 009740-004 from the Department of Homeland Security to the Center for Firefighter Safety Research and Development and training grant # AG000268 from the National Institute of Health. The authors have no professional relationships with companies or manufacturers that might benefit from the results of this study. The results of this study do not constitute endorsement of any product by the authors or the National Strength and Conditioning Association.
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