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Coaches Blog

Heat Acclimation Continued

Training and racing in heat have always been a challenge. It can lead to bad outcomes at races and cause anything from frustration to adverse health effects.

The interaction of heat stress and exercise results in a physiological strain from high core, skin, and brain temperatures, increased cardiovascular strain, a greater reliance on carbohydrate metabolism, and leads to reduced aerobic performance.

Heat stress is caused by several factors:

  • Environmental conditions (temperature, humidity, solar radiation).

  • Physical workload (metabolic heat production).

  • Wearing heavy clothing that impedes heat loss.

The most crucial factor is the athlete's physiological capacity to lose or expel heat.

The main factors that have to be "trained" during the process of heat acclimatization are humidity and mental strategy. The athletes have to train and acclimate to the same climate conditions where they will race. It is not enough to train at similar temperatures where they will compete. It's also necessary to simulate the humidity. Athletes that fail to simulate the humidity of the race location won't adapt and develop the ability to produce enough sweat to cool their skin. Additionally, dealing with high humidity usually requires extra mental fortitude to overcome the extra fatigue.

It is important to remember that body temperature regulation is accomplished through two parallel processes: behavioral and physiological temperature regulation.

Behavioral temperature regulation operates primarily through conscious behavioral adjustments. The athlete can use any method that results in a better-perceived sensation about heat, such as mental mantras, showering, rest, etc.

So, the goal to acclimate to heat should include mental and physical training under the same conditions of the race.

Adapting to heat requires frequent exposure to hot environmental conditions to attenuate the adverse effects of heat stress and boost comfort and confidence levels in hotter, more humid temperatures.

As the body acclimates, athletes notice enhanced sweating and skin blood flow, plasma volume expansion, better fluid balance, cardiovascular stability, a lowered metabolic rate, acquired thermal tolerance, and increased maximal aerobic capacity.

Athletes who train in high temperatures and low humidity don't develop enough number and neural/humoral responses in their sweat glands because, in low humidity conditions, the body doesn't need much sweat to cool the skin.

In high temperature-high humidity climates, the sweat rate must be higher. This is produced by a higher number and a better neural/humoral response of the sweat glands.

Heat acclimation requires up to 8-12 days of workouts in a progressive way for most athletes, as recommended by institutions like the American College of Sports Medicine and the Korey Stringer Institute.

It is essential to simulate the race conditions as closely as possible. Many athletes prepare a temperature-controlled indoor treadmill and bike room. They use humidifiers and heaters to create humidity levels similar to the expected race-day conditions.

These controlled environments allow athletes to practice the hydration and mental strategies while also measuring the sweat rate and other factors every 4 days so athletes can replace fluids correctly and measure the progressive adaptation. Mental strategies can be measured using the perceived comfort (or discomfort) during training.

It is essential to mention that the volume of aerobic exercise must be controlled during the adaptation period: no more than 30 min the first day; increasing daily up to 60 min on day 5, and avoiding anaerobic exercise. It could be increased progressively after day 6, including small intervals of anaerobic exercise on alternating days. The perceived comfort to heat and sweat rate are good parameters to measure adaptation.

After this period, the key workouts may be performed outdoors. The long aerobic workouts could be performed indoors in a controlled climate room.

The first sign of acclimation will be how you feel during the exposure to heat. If you feel more comfortable, you are on the way to having a competitive advantage for your next race in a hot and humid climate.


Manuel Delgado Gaona is a USAT Level II and Youth & Junior Coach, FMTri Level II Certified Coach, an ACSM Exercise Physiologist, and a Physician specializing in Anatomic Pathology. His coaching philosophy is based on exercise efficiency. Coach Manuel can be reached at


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