Heat stress and age: Skin blood flow and body temperature

1. 1. The ability to increase skin blood flow is an important mechanism for transferring heat from the body core to the skin for dissipation. 2. 2. During exercise, skin blood flow is typically 20-40% lower in men and women aged 55 and over (compared with 20-30 years old) at a given body core temperature. Yet criterion measures of heat tolerance (changes in core temperature, heat storage) often show minimal or no age-related alterations. From a series of studies conducted in our laboratory over the past 5 years, the following conclusions can be drawn. 3. 3. When fit healthy older subjects are matched with younger subjects of the same gender, size and body composition, V_O2max, acclimation state, and hydration level, age-related differences in skin blood flow are evident. However, these differences often do not translate into "poorer" heat tolerance or higher core temperatures. 4. 4. The larger core-to-skin thermal gradient maintained by the older individuals allows for effective heat transfer at lower skin blood flows. 5. 5. Furthermore, there is an increased coefficient of variation for thermoregulatory response variables with increasing age. 6. 6. Despite differences in the mechanisms underlying thermoregulation, true thermal tolerance is less a function of chronological age than of functional capacity and physiological health status. 7. 7. While this conclusion is based primarily on cross-sectional studies, it is supported by the results of more recent studies using multiple regression analyses. 8. 8. Implicit in this conclusion is the notion that thermal tolerance, at any age, is a modifiable individual characteristic.