(2) COMPARISON OF HEART RATE AND ESTIMATED AIR CONSUMPTION DURING LIVE-FIRE TRAINING BETWEEN INCUMBENT AND RECRUIT FIREFIGHTERS

Purpose: Firefighters encounter unpredictable and hazardous conditions during live fires that impose substantial cognitive and physical demands. Anecdotally, experienced incumbent firefighters conserve more air in their self-contained breathing apparatus (SCBA) and learn to complete tasks more efficiently to minimize physical strain and maintain output during live burns. However, physiological data comparing incumbents to recruits is limited. This study aimed to compare the heart rate responses and air consumption between firefighter incumbents and recruits during live-fire training. Methods: Thirty incumbents (age=31.2±8.6y, experience=9.7±7.9y) and twenty-seven firefighter recruits (age =24.9±8.8y) participated in controlled live-fire training. Incumbents and recruits were organized into companies of 3-5 members and assigned a specific firefighting task. Heart rate (HR) was continuously recorded (Polar H10, Polar Electro Inc., Lake Success, NY). HR zones were calculated using age-predicted HR max (220-age) and reported as a percentage of total task time to reflect average intensity. Task completion time and SCBA cylinder pressure (pounds per square inch [PSI]) before (PRE) and after (POST) each task were manually recorded. Estimated air consumption (eAC) was calculated as PSI-Pre – PSI-Post and reported as a total air consumed (ΔPSI) and as the eAC rate (ΔPSI/task time (min)) of air consumption. Mean differences (Δ) were calculated by subtracting recruit estimates from incumbents. Mixed-effects models were used to handle the repeated measures from firefighters involved in multiple burns (α=0.05). Effect sizes were calculated using Cohen’s D (d). Results: During live-fire training, incumbents completed tasks in less time (Δ=-8.88min; p< 0.01; d=-1.42) and had lower eAC (Δ=-585psi; p< 0.01; d=-0.80) than recruits though eAC rate was not different (Δ=1.98psi/min; p=0.76; d=0.05). Incumbents spent less time in HR Zone 1 (Δ=-8.21%; p< 0.01; d=-0.68) and more time in HR Zone 5 (Δ=11.29%; p< 0.01; d=0.69) than recruits. No differences were found for HR Zones 2 (Δ=-4.33%; p = 0.21; d=-0.27), 3 (Δ=-1.28%; p=0.68; d=-0.16), and 4 (Δ=3.46%; p=0.27; d=0.21), maximum HR (Δ=-3.58bpm; p=0.31; d=-0.20), or average HR (Δ=2.55bpm; p=0.53; d=0.15). Conclusions: Incumbents executed live-fire training tasks approximately nine minutes faster and with lower total air consumption than the recruits. The higher HR zones seen in incumbents indicates a higher relative intensity consistent with greater work rate while completing tasks. These data suggest that experienced firefighters would be able to perform more total work than recruits per cylinder of air tank. These findings indicate that less experienced firefighters consume air less efficiently than trained firefighters during live-fire training exercises which may have ramifications on initial job performance. Practical Applications: Firefighting demands high-intensity effort and involves operating under extended stressful conditions. Based on our findings, incumbents and recruits both need robust cardiovascular fitness to facilitate sustained performance during firefighting. Experience does not appear to lessen the physical strain but does reduce the respiratory responses to stressful physiological environments. Training programs should thus be progressive and account for this shift in effort. Acknowledgements: This project was made possible in part by Grant Number T32-GM081740 from NIH-NIGMS award to GFM. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIGMS or NIH.