Responses of young and older men during prolonged exercise in dry and humid heat

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Abstract
Summary Eight young, sedentary men (aged 34 years, SD 3) and six older moderately active, unacclimated men (aged 57 years, SD 2) walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [dry bulb temperature (T db) 21°C, relative humidity (r.h.) 43%)], a warm humid (T db 30°C, r.h. 80%) and a hot dry (T db 40°C, r.h. 20%) environment while wearing ordinary working clothes (0.7 c/o). Their oxgen consumption, heart rate (f c), rectal (T re) and mean skin temperature (Tsk), sweat rate (SR), and evaporative rate (ER) were measured during the tests. The ratings of thermal sensation (TS) and perceived exertion (RPE) were assessed using standard scales. In the heat stress tests, the number of experiments discontinued did not significantly differ between the two groups. The mean levels and end-exercise values of T re, Tsk, f c, TS and RPE were not significantly different between the young and older subjects in any of the environments. In the warm humid environment, however, the T re and RPE of the older subjects increased continuously (PT re, RPE, and ER, the older subjects did not exhibit higher f c during exercise in the heat, they were not more hyperthermic and their performance times were similar to the young subjects. Therefore, it was concluded that older calendar age is not necessarily associated with a reduced ability to exercise in a hot environment and other factors, such as physical activity habits and aerobic capacity, may be equally important in determining heat tolerance in the elderly.