Investigation of modulation of skin vasodilator function by exercise training in a hot environment

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Exercise training in a hot environment modulates the controlling system of skin blood flow and sweating, important thermoregulatory functions, in humans. Most of the findings regarding the modulation of skin vasomotor control by exercise training (or heat acclimation) are obtained from studies of nonglabrous (hairy) skin, usually forearm skin, but information about the influence of heat acclimation on glabrous (nonhairy) skin such as the palm is restricted. In this project, we examined the vasomotor responses in the glabrous and nonglabrous skin during whole body heating before and after a 6-day exercise-heat acclimation program. We also examined changes in the control of sweating by heat acclimation by using frequency of sweat expulsion, an index of central sudomotor activity. Eight healthy young volunteers underwent a six-day heat acclimation program [a total of 80-min exercise at 50% peak rate of oxygen consumption in the heat (36℃)]. In the days before and after the heat acclimation program, we examined the local sweating rate at the chest and forearm, frequency of sweat expulsion, and esophageal temperature during whole body heating using a water-perfused suit. As a result, short-term heat acclimation did not change the vascular response in glabrous skin to a raised core temperature but decreased the temperature threshold for vasodilation in nonglabrous skin. It was also suggested that short-term heat acclimation modulates central sudomotor mechanisms, decreasing the temperature threshold for sweating but does not change in the peripheral mechanism for sweating.