Abstract des Autors

This study examined the effectiveness of endurance training and heat acclimation in reducing the physiological strain imposed by exercising in the heat while wearing protective clothing. 7 young men underwent 8 wk of physical training (60-80% VO2max for 30-45 min/d, 3-4 d/wk at <25 deg C) followed by 6 d of heat acclimation (45-55% VO2max for 60 min/d at 40 deg C, 30% rh). 9 other young men underwent corresponding periods of control observation and heat acclimation. Before and after each treatment, subjects completed a treadmill walk (4.8 km/h, 2% grade) in a climatic chamber (40 deg C, 30% rh), wearing in turn normal combat clothing or clothing protecting against nuclear, biological, and chemical (NBC) agents. Criteria for halting this test were: (1) a rectal temperature (Tre) of 39.3 deg C; (2) a heart rate (fc) =>95% of the subject's observed maximum, maintained for 3 min; (3) unwillingness of the subject to continue; (4) the elapse of 120 min. The training regimen increased mean VO2max by 16% and mean plasma volume by 8%. Heat acclimation increased the mean plasma volume of untrained subjects by 8%, but their VO2max remained unchanged. We conclude that neither endurance training nor heat acclimation do much to improve exercise tolerance when wearing NBC protective clothing in hot environments, because any added sweat secretion decreases blood volume and increases discomfort without augmenting body cooling.