Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports

Abstract

Exercise heat acclimation induces physiological adaptations that improve thermoregulation, attenuate physiological strain, reduce the risk of serious heat illness, and improve aerobic performance in warm-hot environments and potentially in temperate environments. The adaptations include improved sweating, improved skin blood flow, lowered body temperatures, reduced cardiovascular strain, improved fluid balance, altered metabolism, and enhanced cellular protection. The magnitudes of adaptations are determined by the intensity, duration, frequency, and number of heat exposures, as well as the environmental conditions (i.e., dry or humid heat).Evidence is emerging that controlled hyperthermia regimens where a target core temperature is maintained, enable more rapid and complete adaptations relative to the traditional constant work rate exercise heat acclimation regimens. Furthermore, inducing heat acclimation outdoors in a natural field setting may provide more specific adaptations based on direct exposure to the exact environmental and exercise conditions to be encountered during competition. This review initially examines the physiological adaptations associated with heat acclimation induction regimens, and subsequently emphasizes their application to competitive athletes and sports.

Fire service instructor's undergarment choice to reduce Interleukin-6 and minimise physiological and perceptual strain

“…All individuals were required to be physically active, >3 times a week, to replicate the average physical activity frequency of firefighters (Elliot et al 2007;Baur et al 2012). Participants also had not suffered from heat illness in the last six months, and had not been involved in heat acclimation training or had >3 consecutive days of heat exposure >25ºC in the previous month (Périard et al 2015). Participants gave informed written consent and completed medical questionnaires before taking part.…”

Short-term, low-volume training improves heat acclimatization in an operational context

“…During these stays, they must often be rapidly operational, despite substantial heat stress that can be induced by clothing that impedes heat loss (battledress), the physical work rate (endogenous heat production), and most of all, the environmental conditions (temperature, humidity, or solar radiation) in these areas. These conditions increase physiological strain, reducing physical (Périard et al, 2015;Székely et al, 2015), cognitive, and psychomotor performance (Cian et al, 2000;Hancock et al, 2007), and increasing the occurrence of exertional heat illnesses, such as exertional heat stroke (Pryor et al, 2015), diseases that are common in worker populations (Marchetti et al, 2016) and especially soldiers (Armed Forces Health Surveillance Bureau, 2017). This problem was recognized more than 200 years ago when Europeans arriving in tropical climates did not adapt their working behaviors and eventually faced heat illnesses (Lind, 1771;Jackson, 1795;Taylor, 2014).…”

“…This problem was recognized more than 200 years ago when Europeans arriving in tropical climates did not adapt their working behaviors and eventually faced heat illnesses (Lind, 1771;Jackson, 1795;Taylor, 2014). Heat acclimation (or more accurately heat acclimatization as heat stress is produced by the environment and not simulated in thermal rooms) alleviates these losses in performance by producing physiological changes that reduce the deleterious effects of heat stress (Périard et al, 2015;Tyler et al, 2016). For more details, Taylor (2014) accurately reports the functional modifications that occur during heat acclimation.…”

“…Indeed, passive heat acclimatization is less efficient than active heat acclimatization by work-induced physical activity (Horvath and Shelley, 1946;Hellon et al, 1956;Joy et al, 1964;Pandolf et al, 1977) or training sessions (Périard et al, 2015(Périard et al, , 2016Racinais et al, 2015;Tyler et al, 2016). To be effective, in terms of heat acclimation-induced physiological modifications, an exercise session performed in the heat should trigger high sweat rates and largely increase core body temperature (Henane et al, 1977;Racinais et al, 2015).…”

“…We chose a short period (5 days) because soldiers or personnel in this context were not available for a longer time and were engaged in their tasks by the end of the first week. This period is also sufficient to induce partial or complete modification of several physiological factors (decreased HR and core temperature at rest and during exercise, increased plasma volume) and improve thermal discomfort (Périard et al, 2015;Racinais et al, 2015).…”