BLOOD PLASMA HYDRATION BIOMARKERS OF FIREFIGHTERS FOLLOWING LIVE-FIRE TRAINING

PURPOSE: Firefighters often perform physically demanding tasks while wearing turnout gear that is insulated to protect them from the external environment. Though protective, such clothing can impair sweat evaporation from the skin, preventing heat dissipation. Additionally, elevated sweat rates can alter plasma electrolyte concentrations, leading to further impairments in fluid homeostasis and thermoregulation during occupational tasks. Therefore, we investigated the effects of live-fire training (LFT) on plasma osmolality and electrolyte concentrations in firefighters. METHODS: 14 firefighters (25.4 ± 8.7 yrs; 177.1 ± 8.6 cm; 82.9 ± 15.1 kg) completed LFT involving 1 hour of fire suppression and search-and-rescue rotations with a 15-minute break halfway through. Firefighters rotated through these tasks multiple times. Urine specific gravity (USG) was used to assess hydration levels. Pre- and post-LFT blood osmolality and electrolyte concentrations (sodium [Na+], potassium [K+], chloride [Cl-]) were collected and tested. T-tests were used to compare changes in plasma osmolality and electrolyte concentrations. RESULTS: Participants arrived euhydrated (1.020 ± 0.006 USG). Plasma osmolality (Pre: 284.4 ± 8.8 vs Post: 276.9 ± 5.4 mmol/L; p = 0.03) and plasma K+ (Pre: 4.3 ± 0.2 vs Post: 4.7 ± 0.2 mmol/L; p < 0.01) were significantly different after LFT. Plasma Na+ (Pre: 134.5 ± 1.21 vs Post: 133.3 ± 1.3 mmol/L; p = 0.06) and Plasma Cl-were not significantly different after LFT (Pre: 100.8 ± 1.8 vs Post: 100.9 ± 1.5 mmol/L; p = 0.95). CONCLUSIONS: Live-fire training led to a significant decrease in plasma osmolality, a significant increase in plasma potassium concentrations, and no significant changes in plasma sodium or chloride. Future research should include further investigations of occupationally relevant protocols by comparing urine and blood osmolality, electrolyte concentrations, and other solutes for more precise understandings of fluid regulation during live-fire training.