Exercise thermoregulation after 14 days of bed rest

Rectal (Tre) and mean skin (Tsk) temperatures and sweating responses were measured during 70-min submaximal supine exercise (relative VO2 43-48%) in seven men (19-22 yr) during an ambulatory-control (AC) period and after three 2-wk bed-rest (BR) periods separated by 3-wk ambulatory recovery periods. During each of the three BR periods they performed isometric exercises (IME) or isotonic exercises (ITE) for 1 h/day or no prescribed exercise (NOE). Mean basal oral temperature decreased from 36.0 to 35.7 degrees C in the last 10 days of the control-recovery periods, but it varied between 35.7 and 35.9 degrees C during BR. In the exercise-temperature test the equilibrium level of Tre for the IME (37.92 degrees C) and NOE (37.75 degrees C) regimens were higher (P less than 0.05) than the AC level of 37.51 degrees C. Mean skin temperatures with the IME and ITE regimens increased by only 0.4 degrees C during exercise, and both equilibrium Tsk values, 31.98 degrees C and 31.87 degrees C, respectively, were lower (P less than 0.05) than the AC values of 32.71 degrees C. There were no significant differences between any of the sweat rates (range, 438-565 g/h) in the four experiments, but calculated skin heat conductances (Hsk) correlated +0.86 with equilibrium levels of Tsk. It was concluded that the excessive increase in Tre during submaximal exercise following BR deconditioning could be influenced by changes in Hsk, but inhibition of sweating may also be a factor.