The current thesis examined local and whole-body heat loss responses during heat stress at rest, exercise and/or pharmacological stimuli as a function of increasing age. The first study examined the effects of age on whole-body heat loss and heat storage during passive exposure to conditions representative of the upper temperature extremes in Canada. The results demonstrate that the cumulative change in body heat content after 2 h of rest was significantly greater in older adults in a hot-dry

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... lder: 212±25; young: 131±27 kJ, P=0.018) and hot-humid (older: 426±37; young: 317±45 kJ, P=0.037) condition. The second study evaluated the maximal capacity of whole-body evaporative heat loss as a function of age and aerobic fitness. The findings demonstrate that whole-body evaporative heat loss was significantly lower in middle-aged untrained (Ex2: 426±34; Ex3:497±17 W) and older (Ex2: 424±38; Ex3: 485±44 W) compared to young (Ex2: 472±42; Ex3: 558±51 W) and middle-aged trained (Ex2: 474±21; Ex3: 552±23 W) males at the end of the last two exercise bouts (P<0.05). The third study assessed the maximal capacity of whole-body evaporative heat loss in females and found that whole-body evaporative heat loss was significantly lower (P=0.002) in the older (Ex2: 343±39 W; Ex3: 389±29 W) compared to the young (Ex2: 383±34 W; Ex3: 437±36 W) females at the end of the second and third exercise-induced heat loads of 325 and 400 W, while no differences were observed during recovery (P=0.693). The fourth study examined nitric oxide-dependent sweating during exercise/rest cycles in young and older adults. We showed that nitric oxide-dependent sweating during short bouts of exercise in the heat is observed in young males, but not in older adults. The fifth study examined: 1) the extent to which peripheral factors (i.e., sweat gland and skin vasodilatory function) contribute to the postexercise suppression of heat loss; and 2) whether age-related differences exist in the mechanisms modulating postexercise heat loss. The findings demonst [...]