Temperature regulation during severe exercise with some observations on effects of skin wetting.

The thermoregulatory responses to severe exercise of 1-h duration have been studied in 11 healthy subjects, and the effects of skin wetting have been examined in 6 of them. Measurements in the laboratory included metabolic (M) and total (H) heat production, rectal (Tre) and mean skin (Tsk) temperatures, evaporative sweat loss (E), and peripheral tissue conductance (K). In addition Tre and changes in body weight were measured in 18 conpetitors following a 20-km road race run at approximately 90% of their maximal oxygen intake (Vo2 max). The results showed that Tre was curvilinearly related to %Vo2 max. In contrast Tsk was independent of M, H, E, and %Vo2 max, and reached similar and constant values at the end of exercise in all subjects. E was appropriate for a given H, but K was lower in the sedentary subjects than in the athletes. Skin wetting had no effect on Tre but reduced E by 10%. It is suggested that the pattern of Tre rise in excercise reflected the nature of the controlling system and was not due to a failure of the heat-dissipating mechanisms.