Firefighter Recruit Responses To Firefighter Specific Training And Correlates Of Physiological Strain

Firefighters (FF) perform strenuous and physically demanding duties in stressful, hazardous, and often unpredictable conditions. Recruits must undergo rigorous training that mimics FF-specific tasks, including prolonged periods of physical exertion and extreme environmental conditions. PURPOSE: To quantify recruits’ physiological responses to FF-specific training in normal vs. hot conditions and to identify correlates of physiological strain. METHODS: Recruits wore monitoring devices on 2 days to measure indices of physiological strain-cardiovascular (CV; average heart rate [HR] expressed as percentage of HRmax), thermal (average core temperature), and musculoskeletal (mechanical intensity [MI]; expressed on 1 to 10 scale) strain-during FF-specific training in normal vs. hot (~77 °C) conditions. Baseline measures included weight, percent body fat (%BF), and mean anaerobic power. Paired samples t-tests investigated differences between training days. Correlations explored associations between recruit characteristics and physiological strain. RESULTS: 17 male recruits ([M ± SD] 21 ± 4y, weight = 87 ± 13 kg; %BF = 17.3% ± 4.9%) achieved below average anaerobic power (6.5 ± 0.7 W/kg). CV strain ([MD ± SD]3.4 ± 5.1% HRmax, p = 0.01) and MI (-0.2 ± 0.1, p < 0.001) differed for normal vs. hot training days; thermal strain did not (0.2 ± 0.3 °C, p = 0.18). %BF was negatively correlated with mean anaerobic power (r = -0.69, p = 0.002); recruit characteristics were not correlated with physiological strain indices. For both conditions, higher CV and thermal strain correlated with lower HR variability (i.e., higher stress and fatigue); correlations were strongest during hot training conditions (r = -0.86 and r = -0.78, both p < 0.001). Higher MI correlated with higher CV and thermal strain (r = 0.51 and r = 0.52, both p < 0.04) during normal training conditions. CONCLUSIONS: Levels of CV strain and MI during FF-specific training differed for normal vs. hot conditions and recruit characteristics were not correlated with physiological strain indices. Further investigation with a larger sample and expanded baseline measures (e.g., aerobic capacity, muscular strength) is warranted, as it may offer additional insight into these relationships and potentially inform decisions regarding FF preparation and training.