Heat Training: Two Weeks to a Real Performance Edge

Fitness is actually a mixed bag. Fitter athletes produce more body heat because they can work harder. Short of changing your body composition – which takes months – the best fix is simple: spend more time exercising in the heat.

Heat training increases your blood volume. More blood means your body can send some to the skin for cooling while still supplying muscles. The effect has been compared to a mild, legal version of blood doping. The science is still debated on exactly how it works, the evidence is strong enough that safely attempting heat adaptation is worth it.

One study in the European Journal of Applied Physiology found that people who made no special effort to exercise in the heat showed no improvement in heat tolerance from spring to fall. Adaptation requires deliberate work.

OSHA recommends that workers on their first day in the heat do only 20% of their usual workload, ramping up to 100% within a week. The U.S. Army's training protocol aims for at least two hours in the heat each day, including cardiovascular exercise. If two hours feels too much, start with what you can handle and work toward that benchmark. After about two weeks you should be significantly better adapted.

If the weather doesn't cooperate, use a sauna after your workout. Fifteen to thirty minutes in the sauna after your core temperature is already elevated from exercise promotes heat adaptation. Skip the workout and you'll need to add about 20 minutes to the sauna time for the same effect.

You can take a few days off from the heat and keep the adaptation. After a week of avoiding heat you start losing it. The Army estimates you lose about 75% after three weeks. To maintain during cool weather, wear extra layers during workouts, or return to the sauna protocol.

The confirming factors that your adaptation is working: your heart rate during a hot run drops, you sweat earlier and more evenly, and you don't feel like stopping after 20 minutes. What would invalidate the adaptation: nausea, dizziness, or a core temperature spike. If symptoms hit, stop and cool down. The two-week investment in heat exposure gives you a real edge. You'll still feel hot, you'll still run slower than in cool conditions. You'll be able to push harder before your body temperature hits dangerous levels. That alone is worth the effort.