Mechanisms of heat acclimation and tolerance induced by exercise training and heat exposure

Abstract

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.

Direct exposure to mild heat promotes proliferation and neuronal differentiation of neural stem/progenitor cells in vitro

“…Heat acclimation (HA) is an adaptive physiological process that increases heat tolerance [ 1 , 2 ]. Heat-acclimated animals exhibit various physiological changes, especially in the thermoregulatory and cardiovascular systems, such as enhanced sweating and cutaneous vasodilation, increased plasma volume, and reduced heart rate [ 1 , 2 ]. Depending on the duration of heat stimuli, the process of heat acclimation is classified into two types, i.e., (1) short-term HA (STHA), and (2) long-term HA (LTHA) [ 3 ].…”

Neural progenitor cell proliferation in the hypothalamus is involved in acquired heat tolerance in long-term heat-acclimated rats

“…In humans and rodents, passive exposure to moderate heat is known to induce heat acclimation, which increases endurance for acute heat stress [ 16 , 17 ]. A large number of studies reported that numerous physiological changes are confirmed in heat acclimated (HA) animals, e.g., enhanced sweating and cutaneous vasodilation, an increase in plasma volume, a decrease in core temperature at rest or during exercise, and reduced heart rate [ 16 , 17 ]. The process of heat acclimation is classified into two types, namely, short-term HA (STHA) and long-term HA (LTHA), depending on the length of the term of heat stimuli [ 18 ].…”