Recurrent Heat Exposure: Effects on Hormonal Responses in Resting and Exercising Men,
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MASS
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Heat acclimatization was induced in a group of healthy young men by walking on a treadmill 5.6 kmhr, 49 C27 C drywet bulb, 90 min day, 7 days, and confirmed by recording significantly reduced final rectal temperatures and heart rates on the 7th day of exercise in the heat. A 2nd group, paired for maximal O2 consumption and body weight, remained sedentary under identical conditions. After correcting for minor changes in hematocrit, both groups demonstrated significant reductions in plasma cortisol on the control day, indicating a strong anticipatory response. Heat exposure reduced plasma cortisol levels in the sedentary men, but the mild exercise program neutralized these effects in the exercising group. Patterns of alteration of growth hormone indicated a significant response even to the mild exercise program described here, while heat stress, pre- and post-acclimatization, seemed to have no effect upon plasma levels. Plasma total T4 levels demonstrated several randomized changes which, however, did not reflect decreased output under the environmental conditions described here for either the walking or sedentary group. The mild exercise program elicited significantly reduced levels of plasma insulin which were not affected by the recurrent heat exposure. While recurrent heat exposure effected hormonal responses among both exercising and sedentary groups, these alterations were not correlated with the process of heat acclimatization.
- Stress Physiology