Disturbance of thermal homeostasis during post-exercise hyperthermia

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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.

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