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

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University of Ottawa, School of Human Kinetics, Ontario, Canada.


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 post-exercise fell to stable values of 37.13, 37.19, 37.29, and 37.55 degrees 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 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.

[Indexed for MEDLINE]

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