Effect of acclimatization to heat on the regulation of sweating during moderate and severe exercise

Sweat regulation in two male subjects, one an athlete in training, was examined over a range of exercise intensities and environmental temperatures. The results after artificial heat acclimatization in the nonathlete showed that sweating rate over 1 h of maximal exercise increased to the same level as the athlete, but his evaporative sweat loss remained significantly (15%) lower. Rectal temperature (Tre) was reduced for a given oxygen intake (VO2) and relative work load (%VO2 max), but the difference in Tre/%VO2 max between the subjects was not significant. At different mean skin temperatures (Tsk), relative sweat rate (%msw, max), for a given Tre was unaffected and the relationship of %mSW, max with Tre was the same in both subjects. Lowering the relative work load (and thus Tre) displaced the Tre/%msw, max relationship to the right, and regression lines for different %VO2 max were parallel. The multiple regression equation %msw, max = -1,531 +/- 36.67 Tre (degrees C) + 6.08 Tsk (degrees C) (r = +0.92), related the parameters and was independent of the subject's fitness and state of acclimatization providing %msw, max was expressed in terms of the appropriate msw, max at the time of measurement.