Chris Carmichael: Train Right Now

By Jim Rutberg

The techniques for staying cool on a hot day are pretty straight-forward: stay hydrated, douse yourself with water, put ice sock/packs in your jersey, etc. But we’ve been getting a lot of questions about how athletes adapt to heat and why some athletes struggle to cope with high temperatures. So, here’s a primer on how athletes adapt to heat:

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What happens as an athlete acclimates to heat?

The human body has an amazing ability to maintain core temperature within a very tight range (97-100 degrees Fahrenheit) despite wild fluctuations in environmental temperatures. When exposed to a hot environment for a prolonged period of time, and especially when exercising in hot and humid environments, your body needs to become more efficient at dissipating heat. As a result, you:
•Start sweating sooner: To stay ahead of rising core temperature, your body kicks your primary cooling system (sweat) into action earlier than when not heat acclimated.
•Sweat more profusely: Your body learns to open the floodgates to get more fluid onto the skin surface for evaporative cooling.
•Sweat more evenly: You have sweat glands all over, and your body needs to increase evaporative cooling you’ll start sweating from everywhere.
•Change the composition of your sweat: The electrolyte content of your sweat decreases as your body tries to pump out more fluid but retain minerals needed for the nervous system and other critical body functions.
•Increase plasma volume: Your blood is what’s transporting heat from your core to your skin for radiant cooling as well as evaporative cooling. Increased plasma volume increases your capacity for heat transfer, and provides fluid for sweat.

Your heart rate response to exercise also changes in hot environments. Athletes experience higher exercise heart rates at a given workload, compared to cooler environments. This increase is much higher for athletes who are not acclimated to the heat, and as you acclimate your exercise heart rates will return to normal. Both acclimated and non-acclimated athletes also experience ‘cardiac drift’ as an acute response to increased core temperature, in order to facilitate heat transfer from your core to your skin/extremities where it can be dissipated through radiation, convection, conduction, or evaporation.

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How long does it take an athlete to acclimate to heat?

The process starts in the first few days you’re exposed to increased temperatures, as long as you’re exposed to the heat for at least an hour each day over the course of consecutive days. It takes between 10-14 days to be completely acclimated to the increased temperatures. NOTE: This is why some athletes who travel to warm climates suffer initially. Acclimation takes time, it’s difficult to accelerate the process, and the process is hindered by dehydration and/or exercise at high intensity levels – which are pretty much impossible to avoid while racing a major stage race through the desert.

What’s the difference between acclimation and acclimatization?

Heat acclimation is a passive process that results from exposure to hot environmental conditions. In other words, acclimation occurs as you’re going about your normal daily activities. Acclimatization is an active process of ‘heat training’, where your activities are designed to improve your performance in hot environments.

How does heat acclimatization work?

The training athletes do when they first arrive in hot environments is an example of acclimatization. Exercising in the heat 60-90 minutes a day for 5-10 days will initiate the physiological changes necessary to perform optimally in the heat. A reduction in intensity and volume is necessary during this time. Reduce your intensity by 60-70% during the first 3-4 days (ride easy for 60-90min), and then gradually increase the intensity and duration of your workouts over the next 3-5 days. Not only does this give your body time to modify your sweat response, but it also gives you time to adapt to consuming and processing an increased amount of fluid. Be sure to drink plenty of fluids and allow your body time to adapt, and you’ll soon be able to increase your exercise intensity in the heat.

Athletes can also perform heat acclimatization training prior to traveling to a hot environment. An example of this occurred before the 1994 Track Cycling World Championships, which were held in Palermo, Italy. The US National Team trained on indoor trainers in a hyperbaric chamber at the Olympic Training Center in Colorado Springs, CO, which was set to replicate the high heat, high humidity, and low altitude (sea level) of Palermo. The strategy worked, and the team earned two golds, two silvers, and a bronze on the way to finishing third in the medal count. At the time it was one of the US team’s best overall performances at the Track World Championships. Simpler methods of acclimatization training include wearing additional layers of clothing, sitting passively in hot sauna (heat exposure) or training in a hot room.

Is it better to perform acclimatization activities before traveling to a hot environment, or once you get there?

Before. Sitting in saunas and training in warm rooms prior to traveling to hot environments is less disruptive to your overall training progress, because the exposure to heat is temporary. When you travel to a hot environment you have to reduce training volume and intensity until your body can handle the heat stress. You can minimize this loss of effective training time by doing everything you can to prepare for the heat prior to arrival. However, keep in mind that no matter much preparation you do before arriving, full acclimation will still take some time.

Should athletes restrict fluid intake in training to adapt to a lower fluid requirement for races in hot conditions?

NO. This idea circulates every few years, but it’s just plain bad. Neither ‘dehydration training’ nor ‘starvation training’ are a good idea. Not only can they be dangerous to your health, they don’t really work either. The physical work you’re doing generates a ton of internal heat – it’s not just the hot air around you that’s the problem – and both sweat and increased blood flow to the skin are your primary means of dissipating that heat and allowing you to continue working. When you restrict fluid intake and hamper your body’s ability to dissipate heat, core temperature rises out of control and your body finds other – less pleasant – ways to slow you down, like diminished focus and motivation, nausea, and dizziness. In part, these are protective measures to get you to stop generating so much heat.

Jim Rutberg is a Pro Coach with Carmichael Training Systems and co-author, with Chris Carmichael, of seven books on training and sports nutrition. For information on CTS coaching, training camps, and Bucket List Events, visit



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