Exercise temperature regulation in man in the upright and supine positions

Abstract

Rectal (T_re), auditory canal (T_ac) and mean skin (T̄_sk) temperatures and various metabolic measurements were taken on five men during 70-min exercise periods, in the upright and supine positions, on a bicycle ergometer at an average relative Vo₂ of 43%. The men were tested under the four combinations of continuous and intermittent (30 sec work-rest cycles) exercise in the upright and supine positions. The purpose was (a) to confirm the elevated T_re with intermittent work; (b) to determine if these higher core temperatures were due to orthostatic reactions; and (c) to determine if the intermittent mode and/or the supine position would modify exercise temperature regulation. In all four experiments sweat rate and energy production were the same. In the upright position equilibrium T_re during intermittent work was 0.13°C higher than in continuous work; in the supine position the comparable intermittent T_re was elevated 0.28°C. The greatest increase in T_re (+ 1.56°C) occurred during the intermittent-supine experiment where the decrease in T_sk (— 0.67°C) was least. Equilibrium T_sk was elevated 0.75°C in the supine position. With similar sweat rates, intermittent exercise results in increased T_re while the supine position includes higher T_sk. The elimination of orthostatic reactions with supine exercise does not attenuate the higher intermittent work T_re. The results indicate nonlinear relationships between sweating and core and skin temperatures and suggest the action of undefined thermal and/or nonthermal inputs in the control of exercise temperature regulation.