Can You Train for Hot Environments?

Step into what appears to be an ordinary walk-in freezer, and you’ll find yourself in a chamber of extremes. Imagine a space where you can shiver in 0°F temperatures, bask in the scorching heat of a desert day, or experience the thin air of a mountain peak at 22,000 feet. This unassuming room has the power to recreate challenging environmental conditions for athletes.

The chamber is a playground of temperature, humidity, and atmospheric manipulation for Dr. Chris Minson, who works with endurance athletes like cyclists and runners to prepare them for races in hot environments. Heat acclimation training could provide these high-level athletes with small-to-moderate performance gains (e.g., in race time) when competing in high temperatures.

What is Heat Acclimation?

Heat acclimation is when the body gradually becomes more resilient to hot environments using artificial means (e.g., a heat chamber). Acclimation differs from acclimatization, which is when physiological adaptations occur due to repeated exposure in a natural hot environment. Without heat acclimation or acclimatization, exercise in hot environments can lead to added thermal and cardiovascular strain due to rising core body and skin temperatures. This, in turn, can result in decreased performance and, in severe cases, dangerous health consequences.

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Who Benefits from Heat Training? 

Dr. Minson cautions that heat training is not for everyone. “Make sure you’ve got your fundamentals down like diet, sleep, recovery, and a training program,” said Dr. Minson. 

High-level athletes are likely to reap the benefits of heat training sooner than untrained athletes. This is because untrained individuals might find it challenging to maintain elevated exercise intensities.¹

Athletes in Dr. Minson’s heat chamber undergoing performance testing. Image credit: Dusty Whitaker

What Improvements Can Athletes Potentially See?

Beyond changes in heat regulation, such as earlier sweat onset, athletes who incorporate heat training experience other physiological adaptations such as greater blood volume, reduced heart rate, improved maximal oxygen uptake, and increased anaerobic threshold.^1,2,3,4

A meta-analysis of 96 studies of heat training demonstrated that the total amount of exercise that can be done in a hot environment can increase by about 23%, while “performance” metrics based on 52 datasets (which combines a variety of outcomes such as the time to complete a 10K run or a 40km cycling time trial) improves about 7%.⁵ The exact process by which all this happens has not been fully mapped out yet, but researchers have found that after heat acclimation, the activation of physiologic processes like sweating and blood vessel widening now happens at a lower core temperature, meaning that the body starts cooling itself earlier and more effectively in response to increased heat. This results in an overall lower body temperature and heart rate while exercising in the same environment after heat acclimation. 

Additionally, heat shock proteins play a role. When exposed to repetitive heat, as in heat acclimation, all cells in the body experience a degree of stress due to increased core body temperature. This stress triggers the production of heat shock proteins, which act as a form of cellular protection against immediate damage caused by heat stress. They also help cells develop tolerance against potential heat stress in the future. For example, cells that were previously “exposed to non-lethal heat shock can survive a subsequent otherwise lethal heat shock.”¹ This all demonstrates that our body is better protected from potentially damaging heat stress after becoming heat acclimated. 

Dr. Minson’s Advice on How to Incorporate Heat Training

There are many different approaches to heat acclimation. Dr. Minson recommends starting under supervision with 20- to 30-minute sessions at around 95°F and gradually building up to 60-minute sessions at 104°F.⁶ He also recommends repetitive sessions – at least 10-14 days cumulatively in the heat – to achieve full performance benefits in the same environmental conditions.^6,7 As heat loss mechanisms like sweating and skin temperature become more efficient, increase exercise intensity to continue to stress the system. Ideally, these heat-training sessions are done in a controlled environment where the athlete can be safely monitored. 

Timing matters too. “It’s important to separate your heat acclimation strategies from your key training days,” said Dr. Minson. For example, if you perform your hard training days on Tuesdays and Fridays, don’t do your heat training on those days. Why?

“If you’re doing those hard intense days in the heat, you’re doing them slower. You’re more fatigued. It’s another stress,” said Dr. Minson. “Do your key workouts in ideal conditions to maximize your performance on that day. After a good rest and sleep, you can add heat as long as it doesn’t disrupt your recovery. Try to get the benefits from both heat acclimation and intense training but not have them interfere with each other.”

How Quickly Does the Body Adapt During Heat Training?

Different physiological adaptations occur at varying rates. Cardiovascular improvements can be seen in just 4-5 days for well-trained athletes, while changes like increased sweat rate may require up to 14 days. Dr. Minson estimates that 75-80% of the acclimation process happens within the first 4-7 days.^1,8,9

The benefits of heat acclimation are not permanent. Any gains you have made will gradually decline if not maintained. This rate of decline follows a similar trend as the gains, meaning the responses that were first to adapt, like improved heart rate, will also be the first to decay. Rate of decay is difficult to study and more research is needed to determine how quickly the decay occurs.

Image provided by Malia Pivec

If athletes cannot undergo heat acclimation in the two weeks leading up to a competition, they can also plan their heat training one month earlier, according to a 2023 International Olympic Committee consensus statement. They can then reintroduce heat acclimation a few days before the event to minimize the decay of adaptation, incorporating biweekly heat exposures in the interim.

Curious to learn more? Stay tuned for future stories on heat training.