Heat Adaptation of Tropic-Dwelling People

Abstract

Adaptation to heat can be acquired through natural or artificial climatic stimuli. As compared to temperate natives, tropical natives have delayed onset of sweating. The sweat onset time tends to decrease with longer duration of stay in temperate zone and lower sodium concentration in sweat. The local amount of evaporation is significantly lower at the lower part of the sub scapular region associated with of higher mean skin temperature (Tsk) and rectal temperature (Tre) during rest, exercise and recovery period in the heat. The set-point of the core temperature is at a higher level in tropical natives. The heat-activated sweat gland density (HASG) is significantly lower at resting levels, and sweat gland density is lower associated with smaller output per single gland. The reduced amount of evaporation rate and delayed onset of sweating in the tropical natives is due to their higher Tsk, which accelerated dry heat loss with a reduction of the rate of sweating as a result significantly lower in dehydration. Tropic-dwelling subjects, although exposed to prolonged passive heat exposure, are not fully heat acclimatized. To achieve further heat acclimation, they need to gradually expose themselves to exercise-heat stress in a hot environment. This may be important for athletes either from tropical or temperate areas who will participate in events all over the world, in different climatic conditions. Environmental adaptation may be relevant in every event. Athletes should undergo re-acclimatization before competition to reduce the adverse effects of environmental temperature change.