The effect of ambient temperature and exercise intensity on post-exercise thermal homeostasis

Abstract

We have previously demonstrated a prolonged (65 min or longer) elevated plateau of esophageal temperature (T _es ) (0.5–0.6°C above pre-exercise values) in humans following heavy dynamic exercise (70% maximal oxygen consumption, V˙O_2max) at a thermoneutral temperature (T _a) of 29°C. The elevated T _es value was equal to the threshold T _es at which active skin vasodilation was initiated during exercise (Th_dil). A subsequent observation, i.e., that successive exercise/recovery cycles (performed at progressively increasing pre-exercise T _es levels) produced parallel increases of Th_dil and the post-exercise T _es, further supports a physiological relationship between these two variables. However, since all of these tests have been conducted at the same T _a (29°C) and exercise intensity (70% V˙O_2max) it is possible that the relationship is limited to a narrow range of T _a/exercise intensity conditions. Therefore, five male subjects completed 18 min of treadmill exercise followed by 20 min of recovery in the following T _a/exercise intensity conditions: (1) cool with light exercise, T _a = 20°C, 45% V˙O_2max (CL); (2) temperature with heavy exercise, T _a = 24°C, 75% O_{2 max} (TH); (3) warm with heavy exercise, T _a = 29°C, 75% V˙O_2max (WH); and (4) hot with light exercise, T _a = 40°C, 45% V˙O_2max (HL). An abrupt decrease in the forearm-to-finger temperature gradient (T _fa −T _fi) was used to identify the Th_dil during exercise. Mean pre-exercise T _es values were 36.80, 36.60, 36.72, and 37.20°C for CL, TH, WH, and HL conditions respectively. T _es increased during exercise, and end post-exercise fell to stable values of 37.13, 37.19, 37.29, and 37.55°C for CL, TH, WH, and HL trials respectively. Each plateau value was significantly higher than pre-exercise values (P < 0.05). Correspondingly, Th_dil values (i.e., 37.20, 37.23, 37.37, and 37.48°C for CL, TH, WH, and HL) were comparable to the post-exercise T _es values for each condition. The relationship between Th_dil and post-exercise T _es remained intact in all T _a/exercise intensity conditions, providing further evidence that the relationship between these two variables is physiological and not coincidental.