Exercise thermoregulation in men after 6 hours of immersion.

Rectal (Tre) and mean skin (Tsk) temperature, skin heat conductance (Ksk), heart rate, and total body sweat rate were measured in 6 men (20-35 years) during 70 min of supine leg exercise (Ta = 23.5 degrees C, rh = 40%) at 50% of their peak O2 uptake (VO2 peak); these data were taken after a 6-h control (C) period in air and after immersion to the neck (NI) in water (34.5 degrees C) for 6 h after overnight food and fluid restriction. After NI mean (+/- S.E.) water balance was -1,285 +/- 104 ml for the 6 h and plasma volume (delta Hb and Hct) decreased by 5.2%. End exercise heart rates after C (141 +/- 3 b X min-1) increased to 148 +/- 3 b X min-1 (p less than 0.05) after NI while Vo2 were both 2.2 L X min-1 Tre increased by 0.5 C degrees (p less than 0.05) between the end of NI and the start of exercise. During exercise following C and NI, delta Tre were +1.0 degrees C and +0.9 degrees C (NS), Ksk were 44 +/- 2 and 43 +/- 1 kcal X m-2 X hr-1 X degrees C-1 (NS), while sweat rates increased from 248 +/- 19 to 366 +/- 52 g X h-1 (p less than 0.05), respectively. Both the total integrated Tre and Tsk curves after NI were higher (p less than 0.05) than for C. These results suggest that, compared with control responses, the equilibrium level of core temperature during submaximal exercise is regulated at a higher level after immersion.