Sweating and skin blood flow during exercise: Effects of age and maximal oxygen uptake

Individuals ≥60 yr of age are more susceptible to hyperthermia than younger people. However, the mechanisms involved remain unclear. To gain further insight, we examined the heat loss responses of 7 young (24-30 yr) and 13 older (58-74 yr) men during 20 min of cycle exercise [67.5% maximal O₂ uptake (V̇O(2 max))] in a warm environment (30°C, 55% relative humidity). Forearm blood flow (FBF) and chest sweat rate (SR) were plotted as a function of the weighted average of mean skin and esophageal temperatures [T(es(w))] during exercise. The sensitivity and threshold for each response were defined as the slope and T(es(w)) at the onset of the response, respectively. When the young sedentary men were compared with a subgroup (n = 7) of the older physically active men with similar V̇O(2 max), the SR and FBF responses of the two groups did not differ significantly. However, when the young men were compared with a subgroup of older sedentary men with a similar maximal O₂ pulse, the SR and FBF sensitivities were significantly reduced by 62 and 40%, respectively. These findings suggest that during a short exercise bout either 1) there is no primary effect of aging on heat loss responses but, rather, changes are associated with the age-related decrease in V̇O(2 max) or 2) the decline in heat loss responses due to aging may be masked by repeated exercise training.