INTRODUCTION: Our lab has recently documented the total energy expenditure during arduous wildfire suppression using the doubly labeled water methodology. The elevated rates of isotopic elimination indicate an arduous working environment that may often compromise energy balance and overall hydration. PURPOSE: The purpose of this investigation was to determine the effects of arduous wildfire suppression on water turnover and changes in body composition in wildland firefighters (WLFF).

METHODS: WLFF (N = 14) were studied during a 5-d period of arduous fire suppression work. A comparison group (N = 13) of recreationally active college students (RACS) was also studied. Water turnover was measured from rates of 2H elimination (rH2O). Urine osmolality, specific gravity, and skinfold measures were also collected.

RESULTS: WLFF demonstrated a decrease in nude body weight (pre = 71.9 +/- 10.4 kg, post = 70.9 +/- 10.2 kg, P = 0.0001) and total body water (pre = 42.9 +/- 7.2 kg, post = 42.0 +/- 6.7 kg, P = 0.0046). RACS maintained total body water and body weight during the experimental period. Isotope (2H2O) dilution demonstrated that rH2O was significantly higher for the WLFF (rH2O = 6.7 +/- 1.4 and 3.8 +/- 1.0 L.24 h-1 for the WLFF and RACS, respectively).

CONCLUSION: These results demonstrate an arduous work environment that threatens hydration, energy balance, and perhaps normal glycogen status.