Physiological changes to heat acclimation

Heat acclimation is an additional strategy competitive athletes may use while preparing for an endurance event taking place in hot/humid conditions. The process of heat acclimation involves adapting to thermal stress via increase in core temperature and sweating through repeated exposure to an artificial environment (heat chamber, hot tub, sauna).

Some adaptations include: decreased core temp during exercise and at rest, decreased skin temperature, decreased heart rate, decreased perception of effort and thermal sensation, increased whole body sweat rate, decreased sodium loss in sweat and urine, increased plasma volume, and increased thirst sensation.

Adaptations take anywhere from 3 to 10 days depending on the physiological response. For example, decreased heart rate and perception of effort takes 3 to 5 days, whereas increased sweat rate and decreased sodium loss in sweat takes up to 10 days. Interestingly, a recent study suggested that some of these benefits were still present for a month after heat adaptation. However, which method (hot water immersion or exercise in the heat) reaps the most benefits is up for debate.

Heat acclimation during exercise can be difficult as it can force athletes to decrease training volume or intensity, compromising the training itself. Therefore, post-exercise hot water immersion (simply using a hot bath) may be preferred by some athletes and has shown to be effective as suggested by a 6-day protocol ( <40 min in 40 deg C/104 deg F post-exercise). Many of these adaptations appear to be retained for ~ 2 weeks or possibly longer, making this an appealing strategy that need not interfere with the pre-race taper. Interestingly, there may be differences in how males and females adapt to heat acclimation protocols…we’ll cover this in our next post!

PMID: 31555140, 34116919, 34127636, 31891914

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