Aging and heat tolerance at rest or during work.

Collectively, the literature on heat tolerance suggests that middle-aged (45-64 year old) men and women are more work-heat intolerant, and suffer more physiological strain during heat acclimation, than do younger individuals. However, it is unclear whether the age differences in work-heat intolerance and physiological strain during heat acclimation are related to age per se or associated with other factors such as certain disease states, decreased physical activity, and/or lowered aerobic fitness. In contrast, the work-heat tolerance and physiological responses during heat acclimation of habitually active or aerobically trained middle-aged men are the same or better than younger individuals. The reviewed studies emphasize the importance of aerobic fitness and pertinent morphological factors, such as body fat, body weight, and surface area in maintaining work-heat tolerance with aging. Recent studies suggest that middle-aged and older men and women may be more susceptible to greater heat strain at physiologically significant levels of dehydration than those younger. However, additional research appears necessary to support this hypothesis. When the effects of chronic debilitating diseases in the elderly (greater than 64 years old) are minimized, their heat tolerance and thermoregulatory responses are comparable to those younger. In fact, healthy and well-acclimated elderly men and women appear to perform as well as those younger during desert walks in dry heat. This review shall discuss experimental observations from previously published studies concerning aging and heat tolerance or the physiological heat strain during heat acclimation at rest or during work; and, will suggest future research efforts needed to advance the area.