Abstract
We examined the effect of rehydration on whole body and local sweating sensitivities during prolonged heavy exercise in a hot environment. Seven healthy male subjects performed 105 min of exercise on a cycle ergometer at 70% of VO2max in a climatic chamber (Ta: 32°C, RH: 60%). The following three conditions were attempted: no rehydration (NR), rehydration in amounts equal to one-half of dehydration (R1), and rehydration in amounts equal to dehydration (R2). Tympanic membrane temperature (Tty), mean skin temperature (Tsk), total sweat loss (TSL) and local sweating rate (LSR) were measured. Whole body sweating sensitivity was calculated as a measure of TSL per degree rise in Tty. Local sweating sensitivity was defined as the slope of a regression line representing the individual LSR and Tty values obtained during the 0, 15 and 33 min exercise transient. Prolonged heavy exercise resulted in the degree of dehydration averaged 2.2, 1.1 and 0.1% BW during NF, R1 and R2, respectively, because of different rehydration levels. However, neither TSL nor LSR was different among all trials. The increased Tty was graded in proportion to the degree of dehydration whereas Tsk response was similar among all trials. Both whole body and local sweating sensitivities were decreased proportionally to the degree of dehydration, and were significantly higher in R2 than in NF. Thus the present study clearly demonstrates that rehydration attenuated the impairment of sweating sensitivity in a graded manner with increased rehydration levels during prolonged heavy exercise in a hot environment. [Jpn J Physiol 54 Suppl:S237 (2004)]
