Combined Effect of Internal and External Cooling between Exercise Bouts on High-Intensity Endurance Exercise Performance in the Heat

Abstract

The purpose of this study was to investigate the combined effect of internal and external cooling between exercise bouts on high-intensity endurance exercise performance in the heat. Six active males completed two trials in a random order: 1） passive rest （control trial） and 2） wearing a cooling vest and ingesting ice slurry （cool trial）．The two experiential trials consisted of two （first and second half）， 30-min cycling exercises （i.e., 25 min of cycling at 55% of maximal oxygen uptake followed by 5 min of time trial） separated by a 15-min half-time break in the heat （i.e., 35.0?C, 50% relative humidity）．In the cool trial, participants worea cooling vest, which can cool the neck, upper body, back, and side, and ingested 5.0 g/kg of ice slurry during half-time break. Time trial performance in the second half was substantially higher in the cool trial compared with the control trial. Rectal temperature at 45, 50, and 55 min and deep forehead temperature at 45 min were substantially lower in the cool trial compared with the control trial. Forehead and mean skin temperatures at 35, 40, and 45 min and neck skin temperature from 35 to 55 min were substantially lower in the cool trial compared with the control trial. Rating of perceived exertion at 50 min and thermal sensation from 35 to 50 min and at 60 and 65 min were substantially lower in the cool trial compared with the control trial. Thermal comfort and recovery rating scale from 35 to 45 min were substantially higher in the cool trial compared with the control trial. In conclusion, combined methods of internal and external cooling between exercise bouts maintained high-intensity endurance exercise performance and decreased core temperature in the initial part of the second half.