Received May 9, 2004
Revised June 1, 2004
Accepted after revision August 12, 2004
Human/environmental and exercise physiology
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Comparison of thermoregulatory responses to exercise in
dry heat among pre-pubertal boys, young adults males, and
older males
Omri Inbar 1*,
Norman Morris 2,
Yoram Epstein 3,
Gregory Gass 2
1 Wingate Institute, Israel
2 Griffith University, Australia
3 Heller Institute, Israel
* To whom correspondence should be addressed. E-mail: inbar{at}wingate.ac.il.
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Abstract |
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Purpose: To compare the thermoregulatory responses during exercise in hot climate among three age categories. Methods: Eight prepubertal (PP), eight young adult (Y), and eight elderly (O) male subjects, cycled at an intensity of 50±1% VO2max for 85 min (three 20-min bouts with three 7 min rest periods) in hot and dry conditions (41±0.1oC, 21±1% RH).
During the exercise-in-heat protocol, rectal temperature (Tre), skin temperatures (Tsk), heart rate (HR), VO2, VCO2, VE, RER, sweat rate, and the number of heat activated sweat glands (HASG) were determined. Results: Despite highest and lowest end-exposure Tre in the Y and O groups, respectively, the rise in rectal temperature (accounting for differences in baseline Tre) was similar among all age groups. Changes in body heat storage (S), both absolute and relative to body mass, were highest in the Y and the O groups and lowest in the PP group. While end-session as well as changes in mean skin temperature were similar in all three age groups, HR (absolute and % of HRmax) was significantly lower for the O compared with the PP and the Y groups. Total body as well as per body surface sweating rate was significantly lower for the PP, while body mass-related net metabolic heat production [(M-W)/kg] and heat gained from the environment were highest in PP and lowest in O. Since mass-related evaporative cooling (Esk/kg) and sweating efficiency (Esk/Msw/kg) were highest in PP and lowest in O, the mass-dependent heat stored in the body (S/kg) was lowest in PP (1.87 ± 0.03 W/kg) and highest in Y and O (2.19±0.08, and 1.97±0.11, respectively). Furthermore, it was calculated that while the O group required only 4.1 ± 0.5 watts of heat energy to raise their body core temperature by 1oC, and the Y needed 6.9 ±0.9 W/1oC, the PP required as much as 12.3 0.7 ±W to heat-up their body core temperature by 1 oC. Conclusions: The results suggest that in conditions similar to those imposed during this study, age and age-related characteristics affect the overall rate of heat gain as well as the mechanisms through which this heat is being dissipated. While pre-pubertal boys seem to be the most efficient thermoregulators, the elderly subjects appear to be the least efficient thermoregulators.
Key Words:
Ageing, Exercise, Thermoregulation
