Most animals can adapt physiologically and biochemically when exposed to altered temperatures for prolonged periods. In humans, marked physiological adjustments are apparent following repeated bouts of core temperature elevation, either from exercise, or high ambient environmental temperatures, or both. In this review, the mechanisms for such adjustments, called "heat acclimation", are discussed. First, the authors focus on thermoregulatory responses in the process of heat acclimation, i.e. how thermoregulation adapts to changes in temperature following repeated exposure to heat and exercise. Once heat acclimation is achieved, skin vasodilation and sweating are initiated at a lower core temperature threshold, and higher sweat rates can be sustained. Second, knowledge regarding the central and peripheral mechanisms for heat acclimation and tolerance is discussed. Recently, two advances - the implication that long-term accommodation to a changing environment involves functional neuronal remodeling associated with transcriptional reprogramming, and the understanding that there is neurogenesis in the hypothalamus - have introduced new concepts to the study of heat acclimation. Although it is still a developing issue, future study will bridge the gap between the classical physiological heat acclimation profile and molecular and cellular mechanisms.
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