An Ultrarunners Guide To Heat Acclimation

Written By Sam Heward

Sam is one of the Ultra X Co-Founders. If he's not actually out running, chances are he's busy writing about it (or plotting Ultra X strategy!)

7 March 2019


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Competing in an extremely hot environment is not only physically grueling but overheating is a serious health risk which needs to be planned for. The effects of hot climates can range from mild performance-inhibiting problems such as heat cramp or exhaustion to more severe conditions such as heat stroke, in which the body’s mechanism to control its own temperature shuts down. By being adapted to the heat, your body can cope better with the stress and you can guarantee a more enjoyable race experience.

Heat acclimation should be a key consideration for athletes looking to succeed in any event in a hot climate, such as Ultra X Jordan or Ultra X Sri Lanka.

How can we adapt?

The good news is that we can adapt to managing at higher temperatures pretty quickly, so runners don’t have to think about it until they start tapering for an event.

Here are a few options:

Heat chamber

If you don’t mind splashing a little cash, heat chambers are the gold standard for heat training as you can control all variables (temperature, kit, pace etc) and therefore simulate the race environment. To optimise the adaptation, it is recommended to do heat acclimation every day for a minimum of five days, but up to 10-14 days before you line up on the start line. These sessions should last between 60 and 90 minutes.


To simulate heat, you could run with a few extra layers of clothing. Aim for about five to ten sessions over a period of two weeks preceeding a race. This is a very basic DIY approach that may work if outdoor temperatures are high enough. When starting out, you should reduce your intensity slightly for the first few sessions to avoid any negative heat-related effects.

Saunas and baths

Using an artificial source of heat such as a sauna or bath can also aid adaptation. It is recommended to train for up to an hour prior doing so. This is so that your core body temperature is already increased, which will allow for greater heat adaptation.

You should start this approach three weeks out from your event for 15 minutes a session, three times a week. Closer to the event, you can increase the duration to 30 minutes, four times a week. Whilst there may also be benefits from solely using the sauna or bath without exercise, exercising at 60% of your VO2 max in the heat produces the quickest results.

Hot Yoga and other methods

Any exercise in a hot environment that raises your core temperature to sufficient levels for a long enough time induces adaptations. To maximise the benefits try to do sessions of 60 mins and raise your heart rate whilst doing so. At the end of the day you want to ensure that you are doing something which fits in with your life and if hot yoga is something that appeals more than sitting in a sauna every day then go for it!

Why it’s worth it

Sweat rate

By spending a little time adapting pre-race, your sweat rate increases and you begin to sweat faster. This means that more sweat can evaporate and you can cool down more efficiently. In addition, the body adapts to lose less sodium which helps to maintain the correct salt balances (meaning you are less prone to heat stress during the race).

Physical adaptation

Your perceived rate of exertion at high temperature decreases as your body gets used to working in the heat. If done correctly, there will be a reduction in the core temperature compared to the same effort before acclimation. Since the body is now losing more fluid through sweat (see above), the blood volume increases so that blood pressure can be more easily maintained and the heart rate will be lower.

Perceived exertion

Aside from becoming better equipped to function when the sun comes out, there are noted performance benefits of heat acclimation that go beyond being ready to survive in the extremes. Not only does heat acclimation benefit you when it comes to hot runs and races, but research shows that it aids performance in cooler temperatures as well. Essentially, heat acclimation should make the hard efforts several percentage points easier and can boost VO2 max.

Runner Filling Water Bottle at Ultra X Jordan


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