Thermal effects of prolonged treadmill exercise in the heat.

Six trained men 21-38 yrs old ran 19-29 km (1.5 to 2.5 hrs) approximately 75% of their VO2 max on a level treadmill in the heat (33.5/21.5 degrees C db/wb, wind velocity 36 m/min). Every 20 min while running they (a) drank 200 ml of 10 degrees C water, (b) drank 200 ml of water at core body temperature, or (c) sponged their faces, arms, and trunks for 2 min with a towel soaked in 10 degrees C water. In another series of experiments each subject (d) hydrated 30 min before the run by drinking 1 liter of water, (e) hydrated and performed (a) above, and (f) hydrated and performed (b) above. Rectal temperature (Tre) and body weight loss (WL) were determined every 30 min and metabolism at 45 min of running. Terminal Tre after (a) through (f) averaged 39.1, 39.3, 39.9, 39.7, 39.1, and 39.3 degrees C respectively. During a control run the corresponding mean Tre was 39.9 degrees C. In a 66.7 kg man with a body weight/surface area (BW/SA) ratio of 37.5 and running at 74% of his VO2 max, Tre rose 0.4 degrees C/1% WL with increasing WL's greater than 2.0% of his initial body weight regardless of the intervention imposed. In another subject weighing 70 kg with a BW/SA ratio of 38.8 and running at 83% of his VO2 max, Tre rose 0.49 degrees C/1% WL over the entire range of WL's.(ABSTRACT TRUNCATED AT 250 WORDS)