Exercise temperature regulation in man in the upright and supine positions

Abstract

Rectal (Tre), auditory canal (Tac) and mean skin (T̄sk) 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 Tre 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 Tre during intermittent work was 0.13°C higher than in continuous work; in the supine position the comparable intermittent Tre was elevated 0.28°C. The greatest increase in Tre (+ 1.56°C) occurred during the intermittent-supine experiment where the decrease in Tsk (— 0.67°C) was least. Equilibrium Tsk was elevated 0.75°C in the supine position. With similar sweat rates, intermittent exercise results in increased Tre while the supine position includes higher Tsk. The elimination of orthostatic reactions with supine exercise does not attenuate the higher intermittent work Tre. 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.