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, short-term aerobic training could replicate the improved physiological responses to exercise-heat stress observed in individuals with a high level of aerobic fitness. Males of moderate (MF; <50 ml x kg(-1) min(-1) VO2peak, n = 8) and high (HF; >55 ml x kg(-1) x min(-1) VO2peak, n = 8) aerobic fitness walked at 3.5 km x h(-1) in the heat (40 degrees C, 30% relative humidity) wearing nuclear, biological, and chemical protective clothing. Tests were conducted once on HF subjects and on MF subjects before (MF-Pre) and after (MF-Post) a 2-week program 6 d x week(-1) of daily aerobic training (1 h treadmill exercise at 65% VO2peak for 12 d, 22 degrees C, 40% relative humidity). The training significantly increased VO2peak by 6.5%, while heart rate (fc) and rectal temperature (Tre) rise decreased during exercise in a thermoneutral environment. HF had lower body mass and body fat content than MF, and VO2peak remained lower in MF 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 fc, Tre, or tolerance time (TT). No significant differences during the first 60 min in Tre and fc were observed between the MF-Post and the HF subjects, though the HF subjects exhibited a lower Tsk. The endpoint Tre, deltaTre, and TT remained significantly higher in HF than in either the MF-Pre or MF-Post subjects. It was concluded that, in preparation for exercise in an uncompensable heat stress environment, short-term aerobic training offers little, if any, benefit and is not an adequate substitute for a high level of aerobic fitness resulting from habitual exercise and training.
Cheung
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Defence and Civil Institute of Environmental Medicine, Human Protection and Performance Section, Toronto, Ont., Canada.
McLellan
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TM
D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D001831:Body Temperature; D005080:Exercise Test; D005081:Exercise Therapy / Q000379:methods*; D017079:Exercise Tolerance; D006339:Heart Rate; D018882:Heat Stress Disorders / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology* / Q000517:prevention & control*; D006801:Humans; D006813:Humidity; D008297:Male; D010101:Oxygen Consumption; D010809:Physical Fitness; D011481:Protective Clothing / Q000009:adverse effects; D011659:Pulmonary Gas Exchange; D013546:Sweating; D013997:Time Factors