Why Endurance Exercise Is Impaired In Hot Environments & How Your Body Adapts

In general exercise performance is impaired in a hot environment due to a greater increase in core body temperature (compared to a cooler environment).

This rise in body temperature can further be exacerbated as exercise intensity increases. With this higher core temperature, an individual has the inability to lose heat, risks hyperthermia, and may experience severe dehydration. Further impairments can be explained by 5 variables.

• First heat related muscle fatigue can occur during prolonged and intermittent exercise in a hot environment.
• There is also an accelerated rate of glycogen metabolism which can lead to increased lactate accumulation and a decrease in muscle pH; both of which lead to muscle fatigue.
• Exercise performance in a hot environment might also be impaired due to an increase in free radical production. These free radicals damage key contractile proteins and inhibit the muscle’s ability to generate force.
• Additionally, there is reduced muscle blood flow when high-intensity exercise is performed in a hot environment. This reduction is due to the competition for blood between the working muscles and the skin; where the skin needs the blood to assist in cooling the body.
• Lastly, high brain temperature can occur when exercising in a hot environment and can impair performance via a reduced neuro muscular drive which would lead to a reduction in motor unit recruitment.

How the Body Adapts To Training In The Heat

There are several adaptations that occur during heat acclimation the results in a lower heart rate and core temperature during exercise:

• First, there is an increase in plasma volume which helps maintain blood and stroke volume, sweating capacity, and allows the body to store more heat with smaller temperature gain.
• There is also an earlier onset of sweating and an increase in sweat rate which equals less heat storage at the beginning of exercise, a lower core temperature, and more evaporative cooling.
• Sodium chloride loss in sweat is also reduced which reduces the risk of electrolyte disturbances.
• Lastly, as the body adapts to the heat there is an increase in heat shock proteins that help prevent cellular damage and a reduction in skin blood flow.

In sum, these adaptations result in a reduced heart rate during exercise, a decreased core temperature and rating of perceived exertion, and ultimately improved performance in a hot environment. Additionally, all these adaptations occur in a period of 3-15 days with heart rate decreases occurring between day 3-7, plasma volume increases occurring between day 3-6, perceived exertion decreases occurring between day 5-9, and an increase in sweat rate that occurs between day 8-14.