The influence of exercise intensity on heat acclimation in trained subjects


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Abstract

HOUMARD, J. A., D. L. COSTILL, J. A. DAVIS, J. B. MITCHELL, D. D. PASCOE, and R. A. ROBERGS. The influence of exercise intensity on heat acclimation in trained subjects. Med. Sci. Sports Exerc., Vol. 22, No. 5, pp. 615–620, 1990. Low-intensity exercise (≤50% V̇O2max) has been demonstrated to produce heat acclimation (HA) in trained subjects. The purpose of this study was to determine whether shorter-duration, moderate-intensity exercise would also result in HA. Nine trained runners performed two 9-d exercise heat-stress protocols. Each protocol consisted of a 90-min heat tolerance test on days 1 (HTT1) and 9 (HTT2). On days 2–8 the subjects exercised at 50% V̇O2max for 60 min·d−1 (T50) or at 75% V̇O2max for 30–35 min·d−1 (T75). Final HTT2 heart rate and rectal temperature (Tr) were significantly (P < 0.001) reduced, as compared to HTT1, with no differences between T50 and T75. Both protocols resulted in significant (P < 0.05) reductions in HTT2 pre-exercise Tr and total exercising caloric expenditure, both of which are known to contribute to HA. No changes in resting plasma volume, osmolality, protein, post-HTT aldosterone, and exercising sweat rate were observed. These results demonstrate that equal levels of HA were obtained with T50 and T75, which suggests that moderate-intensity, short-duration exercise in the heat can produce HA in trained subjects.

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