Abstract

6 trained men (21-38 yrs) ran 19-29 km (1.5-2.5 hrs) at approximately 75 VO2max on a level treadmill in heat (33.5/21.5 deg C db/wb, wind velocity 36 m/min). Every 20 min while running they a) drank 200 ml of 10 deg 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 deg 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 deg C respectively. During a control run the corresponding mean Tre was 39.9 deg C. In a 66.7 kg man with a body weight/surface area (BW/SA) ratio of 37.5 and running at 74 VO2max, Tre rose 0.4 deg C/1 WL with increasing WLs 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 VO2 max, Tre rose 0.49 deg C/1 WL over the entire range of WLs. These data indicate: 1) rise in Tre during prolonged work in the heat is related to the WL incurred; 2) consuming 1 liter of warm or cold water on the run is more effective in preventing a marked rise in Tre than drinking an equal volume of water 30 min before the run; and 3) sponging is ineffective in preventing hyperthermia. Verf.-Ref.