Want to Boost Your Performance? >> Learn All About Heat Acclimation

Looking forward to running in the sun? Don’t get hot under the collar with this super effective way of adapting to the heat.

Wonder Stuff — What Is Heat Acclimation?

Ok, we’re not a fan of “wonder” anything. Wonder foods. Wonder drugs. Whatever. But this technique for improving performance in the heat might just be the stuff of miracles. Cue the — quite frankly — revolutionary concept of hot water immersion. Are you sitting comfortably? Then let’s begin.

Heat acclimation…

…is the process of adaptation that occurs with repeated heat exposure. The theory is that once adapted, you can run faster in the heat — even in cooler temperatures.(1),(2) Various methods have been tried and tested with some success(3) but for those of us not in lab coats, the idea of running to exhaustion in tropical heat with a rectal thermometer inserted is neither attractive nor realistic.

That’s where the experts at Bangor University in Wales come in. These clever scientists have developed an ultra-simple, user-friendly way of adapting to the heat which you can do at home and can improve cardio performance such as running.(4) Sounds too good to be true? It gets better. This technique costs next to nothing and is explained right here. First though, let’s look at what happens when we exercise in the heat.

Follow These 4 Steps to Stay Safe in the Heat

  1. Listen to your body
    If you feel uncomfortably hot, stop and cool down. Look out for these signs of heat exhaustion: dizziness, headache, cramps, nausea, diarrhea, rapid pulse, excessive sweating and cool, clammy skin.
  2. Look after your skin:
    We all love sunny days, but remember to protect your skin with a medium to high spf sun cream. You might need to reapply after sweating!
  3. Wear the right clothing:
    Avoid cotton and opt for synthetic fabrics that allow easy evaporation. Lighter, morebreathable footwear will help you lose heat through your feet. Sunglasses and a hat will protect your head and eyes from the glare of the sun.
  4. Stay hydrated:
    We need water for sweating and for getting oxygenated blood to our muscles. Use the dehydration stat in the Runtastic app (available for Premium users only) to top up after your workout. (Find it in your workout summary along with speed and elevation)



Feeling the Heat

If you’ve ever felt the strain of intense heat or exercise, imagine what happens when the two are combined. Exercise in the heat is a double dose of stress. The muscles and skin compete for blood flow in an attempt to maintain oxygen supply and lose heat. It’s a classic catch-22 and it can leave you dehydrated and breathing hard well below your normal exercise intensity.

When our central nervous system…

…senses an increase in temperature, around 3 million sweat glands enable water to be released at the skin. This amazing heat loss mechanism keeps our bodies from overheating, but it also means we lose fluid. More than half of our blood is water, and this water is literally sweated out. In hot conditions, sweat rates of 1L per hour are common (3.7L per hour being the highest recorded(5), resulting in rapid fluid loss.

Ever felt that breathless, heart-thumping sensation when you run in the heat?

The net effect of this dehydration and increased skin blood flow means we have less blood volume available for the muscles and the heart struggles to make up the deficit.

 Not surprisingly, all of this extra strain impacts performance.


…have shown that time to exhaustion in hot (>30°C) conditions is reduced by a whopping ~45% compared to lower temperatures.(6)

If your performance has ever suffered in the heat, then it’s time to consider heat acclimation — and it’s easier than you think.

Soak up the Sun: Heat Acclimation by Hot Water Immersion

The hot water immersion (HWI) method of heat acclimation is quickly gaining popularity, challenging the traditional ice bath as the post-exercise treatment of choice.

 The real beauty of the HWI method is its simplicity. Go for a run, soak in a hot bath, repeat each day. In a recent study,(7) Mike Zurawlew and Neil Walsh demonstrated the effectiveness of post-run hot baths in promoting heat acclimation and enhancing performance. In this study, 5K run time in the heat (30°C) was improved by 4.9% after hot water immersion.

How To — The Hot Water Immersion Method

  1. Exercise at moderate intensity for ~40 min in temperate conditions — “you should feel warm, but comfortable.”
  2. Immediately take a bath at 40°C (104°F) for 40 min, immersed up to the neck.
  3. Increase bathing time by 5 min each day for a total of 6 days.

 CAUTION! If you feel too hot, get out and cool down. Sit for a few minutes to recover.

Zurawlew, Walsh, Fortes and Potter;
Scand J Med Sci Sports 2016

Zurawlew and Walsh went one step further last year, showing that HWI can induce heat acclimation and improve performance in both highly trained and recreational individuals.(8) This is huge. It means whether you are an experienced marathoner or approaching your first 5K, HWI can work for you.

 In both studies, 6 hot baths were enough to increase thermal comfort, lower core temperature, and quicken the onset of sweating. Other key hallmarks of heat acclimation include reductions in sweat electrolyte concentration and heart rate, and increases in total body water levels, blood plasma volume, and skin blood flow — all of which will benefit your performance in the heat.(9)

 Based on the findings of this landmark study, Professor Walsh, Director of the Extremes Research group at Bangor University, has developed a practical strategy for heat acclimation. This HWI method requires only 6 days to achieve significant results, with heat exposure gradually increased from 15 minutes on the first day to 40 minutes on the sixth day.

Altitude acclimatization is known by the phrase “live-high, train-low.” According to Professor Walsh, “the new mantra should be ‘Train-Cool, Bathe-Hot’.

So there it is; your weapon against the heat. Run, Soak, Repeat!

Use the guidelines in this article to get heat acclimated safely

Only attempt this heat acclimation strategy if you are healthy and do not have a heart condition. Ask your doctor if you are unsure. The beneficial effects of heat acclimation remain for up to two weeks,(10) so if you’re preparing for a specific event in the heat, schedule your heat acclimation strategy in the 14 days prior.


Abe Ankers Abe’s background in sports science and exercise physiology comes in handy when he’s running and cycling. He likes to share his insights with others. View all posts by Abe Ankers