Body temperature in sedentary adults during moderate exercise: no effect from exercise the day before.
BACKGROUND
Epidemiological findings show a continued presence of exertional heat injury during military basic recruit training. Current guidelines do not consider the carry-over effects of prior exercise or exposure to high ambient temperatures on the risk of succumbing to heat illness.


OBJECTIVE
From the epidemiological evidence we hypothesized that both prior exercise and exposure to hot environments on the day before would increase the core temperature response during exercise the next day.


METHODS
Seven sedentary and non heat-acclimated men and women each performed eight randomized exposures involving treadmill walking for a maximum of 2 h every 2 wk. Two separate control trials at a wet bulb globe temperature (WBGT) of 22.5 degrees C and 26.5 degrees C consisted of exercise during the morning only. Six experimental trials involved successive days of exercise with trials on the second day at either a WBGT of 22.5 degrees C or 26.5 degrees C. All of the experimental trials involved walking during the first morning at a WBGT of 22.5 degrees C. Further, four of these trials included additional exercise in the afternoon at either a WBGT of 22.5 degrees C (two trials) or 29.5 degrees C (two trials).


RESULTS
There was no impact of prior exercise on the day preceding the tests at either WBGT for any of the dependent measures. Rectal temperatures increased to 38.0 degrees C at the WBGT of 22.5 degrees C and to 38.5 degrees C for trials at 26.5 degrees C. There were also no carry-over effects from exercise conducted during the preceding afternoon.


CONCLUSIONS
Under situations where individuals are well hydrated, rested, and free of injury, illness, and drug use, repeated exercise bouts on successive days do not alter the thermoregulatory response to exercise.
McLellan
T M
TM
Operational Medicine Section, Defence Research and Development Canada, Toronto, ON. tom.mclellan@drdc-rddc.gc.ca
Rhind
S G
SG
Bell
D G
DG
D000328:Adult; D001831:Body Temperature; D001833:Body Temperature Regulation; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D010101:Oxygen Consumption; D012007:Rectum / Q000502:physiology