Disturbance of thermal homeostasis during post-exercise hyperthermia

Abstract

The response of core temperature to exercise was investigated during recovery in order to avoid the antagonistic competition between exercise and thermal reflexes for the same effector systems which control skin blood flow. Five healthy, non-training males [mean (SD) age, 23.8 (2.04) years] were habituated to 29° C at relative 50% humidity for more than 2 h and then exercised by treadmill running at about 75% maximum oxygen uptake for 18 min. They then remained at 29° C for up to 65 min of recovery. Oesophageal (T _es), rectal (T _re) and skin temperatures (T _sk) were recorded at 5-s intervals throughout. The abrupt fall of temperature gradient from the forearm to finger was used to identify the T _es for skin vessel dilatation (T _dil) during exercise. Mean (SE) Ts rose from a resting value of 36.67 (0.15)° C to 38.22 (0.24)° C, mean T _re rose from 37.09 (0.25)° C to 38.23 (0.15)° C, and T _dil occurred at 37.39 (0.32)° C. Within 10 min of recovery mean T _es fell to 37.31 (0.24)° C, where it remained a significant 0.64° C above its pre-exercise (PrEx) level (P≤0.018) but insignificantly different from T _dil for the remaining 55 min of recovery. Meanwhile, T _re fell gradually throughout recovery to 37.64 (0.18)° C. The T _sk at all non-acral sites except the thigh had recovered to PrEx levels by 20–30 min post-exercise (PoEx). The rapid PoEx fall of T _es to the level of T _dil and the subsequent plateau above PrEx values suggests that heat dissipation during recovery was primarily passive once T _es had fallen to T _dil, even though T _es and T _re were significantly elevated. The relationship of these results to the set-point and load error concepts of thermal control is discussed.