Intramuscular temperatures during exercise in the heat following pre-cooling and pre-heating

Pre-cooling improves heat tolerance and time to exhaustion in the heat. We tested the possibility that reduced tissue temperatures may explain this phenomenon, using three whole-body treatments: pre-cooling, thermoneutral (control) and pre-heating. Pre-cooling reduced muscle temperature (T-m) by 6.3 degreesC while pre-heating increased T-m 3.4 degreesC, relative to control. Despite this offset, T-m climbed towards a common asymptote, with pre-cooling offering no thermal protection beyond similar to40 min. Following pre-cooling, exercising oesophageal temperature (T-es) initially increased at 0.09 degreesC min(-1), being significantly faster than control (0.05 degreesC min(-1)) and pre-heated conditions (0.03 degreesC min(-1)). Pre-cooling lowered the sweat threshold and also resulted in a reduced cardiac frequency across the exercise-heat exposure. Our observations do not support the hypothesis that pre-cooling reduces T-m at the end of an exercise-heat exposure, thereby delaying the development of fatigue. (C) 2004 Elsevier Ltd. All rights reserved.