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 °C while pre-heating increased T m 3.4 °C, relative to control. Despite this offset, T m climbed towards a common asymptote, with pre-cooling offering no thermal protection beyond ∼40 min. Following pre-cooling, exercising oesophageal temperature ( T es) initially increased at 0.09 °C min −1, being significantly faster than control (0.05 °C min −1) and pre-heated conditions (0.03 °C 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.