Comparison of short-term aerobic training and high aerobic power on tolerance to uncompensable heat stress

This study investigated whether, in subjects of moderate aerobic fitness, s hort-term aerobic training could replicate the improved physiologjcal respo nses to exercise-heat stress observed in individuals with a high level of a erobic fitness. Males of moderate (MF; <50ml.kg(-1).min(-1) O-2 peak, n = 8 ) and high (HF; >55 ml.kg(-1).min(-1) Vo(2)peak, n = 8) aerobic fitness wal ked at 3.5 km.h(-1) in the heat (40 degrees C, 30% relative humidity) weari ng nuclear, biological, and chemical protective clothing. Tests were conduc ted once on HF subjects and on MF subjects before (MF-Pre) and after (MF-Po st) a 2-week program 6 d.week(-1) of daily aerobic training (1 h treadmill exercise at 65% Vo(2)peak for 12 d, 22 degrees C 40% relative humidity). Th e training significantly increased Vo(2)peak by 6.5%, while heart rate (ic) and rectal temperature (Tre) rise decreased during exercise in a thermoneu tral environment. HF had lower body mass and body fat content than MF, and Vo(2)peak remained lower in IMF pre-or post-training. In the heat, MF-Post had a decreased skin temperature (Tsk) and an increased sweat rate compared with MF-Pre, but no changes were observed in ic, Tie, or tolerance time (T T). No significant differences during the first 60 min in Tre and fe were o bserved between the MF-Post and the HF subjects, though the HF subjects exh ibited a lower fsk. The endpoint Tie, Delta Tre, and TT remained significan tly higher in HF than in either the MF-Pre or MF-Post subjects. It was conc luded that, in preparation for exercise in an uncompensable heat stress env ironment, short-term aerobic training offers little, ii any, benefit and is not an adequate substitute for a high level of aerobic fitness resulting f rom habitual exercise and training.