INFLUENCE OF HYDRATION STATUS AND FLUID REPLACEMENT ON HEAT TOLERANCEWHILE WEARING NBC PROTECTIVE CLOTHING

The purpose of the present study was to investigate the influence of h ypohydration and fluid replacement on tolerance to an uncompensable he at stress. Eight healthy young males completed a matrix of six trials in all environmental chamber, set at 40 degrees C and 30% relative hum idity, while wearing nuclear, biological, and chemical protective clot hing. Subjects performed either light (3.5 km . h(-1), 0% grade, no wi nd) or heavy (4.8 km . h(-1), 4% grade, no wind) treadmill exercise co mbined with three hydration states [euhydration with fluid replacement (EU/F), euhydration without fluid replacement (EU/NF), and hypohydrat ion with fluid replacement (H/F)]. Hypohydration of 2.2% body mass was achieved by exercise and fluid restriction on the day preceding the t rials. No differences in the endpoint mean skin temperature ((T) over bar(sk)), sweat rate, or rectal temperature (T-re) were observed among the hydration conditions for either work rate. During light exercise, the change in T-re (Delta T-re) was significantly higher with H/F tha n EU/F after 40 min, and heart rate was greater after 25 min. The hear t rate was greater during EU/NF than during EU/F after 60 min. Toleran ce times were significantly greater for EU/F than for either EU/NF or H/F. With heavy exercise, no differences in Delta T-re were observed a cross hydration conditions. Compared to EU/F, heart rates were higher after 10 and 30 min for H/F and EU/NF, respectively. Tolerance times w ere significantly less during H/F than with either of the EU condition s. Stroke volume was significantly decreased in H/F trials compared to EU/F trials for both light and heavy work rates, but no differences i n cardiac output were observed. It was concluded that even minor level s of hypohydration significantly impaired exercise tolerance in a seve rely uncompensable heat stress environment at both light and heavy exe rcise intensities.