Sex-Differences In Physiology During Simulated Firefighting Tasks Following Acute Exercise

PURPOSE: Previous research has shown acute on-shift exercise impacts firefighter job performance, yet it is unclear if varying methods of exercise impact performance differently or if males and females respond differently. We aimed to understand sex-differences in performance and physiological responses during simulated firefighting tasks (SFT) following resistance and aerobic exercise. METHODS: 32 participants (M/F: 17/15; 25.2 ± 4.1 yrs; 173.8 ± 9.8 cm; 75.6 ± 13.2 kg) completed three acute exercise trials in quasi-randomized order: resistance exercise (R), aerobic exercise (A), and rested control (C). Each trial was followed by a SFT (4 rounds: 10 deadlifts (85 or 135lbs) and a 0.15-mile 40 lb-sandbag carry) in an environmental chamber (35 °C; 50% humidity). Pre-trial urine specific gravity (USG) was assessed using a portable refractometer. Body surface area (BSA) was calculated using height and weight. Heart rate (HR), skin temperature (ST), and estimated core temperature (CT) were recorded via an Equivital LifeMonitor. Post-SFT blood lactate (BL) was measured via Lactate Plus Meter. Time to complete (TTC) the SFT was also assessed. Repeated measures ANOVAs were used to compare differences by condition. T-tests were used to compare BSA and USG by sex. RESULTS: Average HR (C: 149 ± 16; A: 166 ± 12; R: 160 ± 13 bpm) and CT (CON: 37.6 ± 0.4; AE: 38.7 ± 0.3; RE: 38.4 ± 0.5 °C) were different between conditions (ps < 0.01) regardless of sex. Average ST during the SFT (M: 37.0 ± 0.8; F: 36.8 ± 0.8 °C) was higher in males compared to females (p < 0.01) regardless of condition. Independent of condition, TTC (M: 1038.8 ± 191.6, F: 1349.8 ± 232.1 sec) and BL (M: 9.2 ± 3.5; F: 6.4 ± 2.9 m/Mol) were higher in males compared to females (p < 0.01). BSA (M: 2.06 ± 0.11; F: 1.71 ± 0.10 m2) was higher in females compared to males (p < 0.01) and USG (M: 1.014 ± 0.004; F: 1.016 ± 0.008) was not significantly different between males and females (p = 0.37). CONCLUSIONS: Acute exercise prior to SFT does not differentially impact physiology or performance based on sex. However, physiological responses during SFT do differ by sex. BSA and SFT intensity (higher BL and faster TTC) may explain higher skin temperatures in males. BSA is more likely responsible than SFT intensity as there were no differences in core temperature between males and females.