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

We have previously demonstrated a prolonged (65 min or longer) elevated plateau of esophageal temperature (T-es) (0.5-0.6 degrees C above pre-exercise values) in humans following heavy dynamic exercise (70% maximal oxygen consumption, VO2max) at a thermoneutral temperature (T-a) of 29 degrees 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 degrees C) and exercise intensity (70% VO2max) 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 degrees C, 45% VO2max (CL); (2) temperature with heavy exercise, T-a = 24 degrees C, 75% VO2max (TH); (3) warm with heavy exercise, T-a = 29 degrees C, 75% VO2max (WH); and (4) hot with light exercise, T-a = 40 degrees C, 45% VO2max (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 degrees C for CL, TH, WH, and HL conditions respectively. T-es increased during exercise, and end postexercise fell to stable values of 37.13, 37.19, 37.29, and 37.55 degrees C for CL, TH, WK, and HL trials respectively. Each plateau value was significantly higher than preexercise values (P < 0.05). Correspondingly, Th-dil values (i.e., 37.20, 37.23, 37.37, and 37.48 degrees 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.