What's Cool In Road Cycling

Can You Heat Adapt With Lots of Clothing Indoors?

Endurance performance is impaired in the heat, and the best way to prepare is to heat adapt. We don’t all have access to heat chambers or saunas, but can we instead effectively acclimate on our indoor trainers by wearing lots of clothes?

Doha - Qatar - wielrennen - cycling - radsport - cyclisme - Amialiusik Alena (Belarus / Canyon Sram Racing) - Knetemann Roxane (Netherlands / Rabobank Liv Women Cycling Team) pictured during TTT women Team Time Trial of the UCI Road World Championships 2016 in Qatar. - photo Davy Rietbergen/Cor Vos © 2016

Any of us who tuned into the Tokyo Olympics, or when Qatar hosted the World Athletics Championships in 2019 and the UCI Worlds in 2016, should hopefully know that heat can seriously impact not just performance but health. This is true for both athletes and workers. Studies tracking World Athletics Championships suggest that any track competition over 400-800 m, or about 1-2 minutes, are worse when done in the heat.

There are lots of fancy things we can do to minimize heat impacts as athletes, including precooling, ice vests/socks, and ice slushie drinks. However, those are all marginal gains compared to systemic and progressive adaptation through gradual exposure to exercise in the heat.

There are many modes of heat adaptation, but they require equipment like my fancy environmental temperature, or saunas or hot tubs. What about the simplest method of all, namely training indoors while bundling up with lots of clothes? That’s the focus of a new Scandinavian study featured in our video today.


Lundby C, IS Svendsen, T Urianstad, J Hansen, B Rønnestad. Training wearing thermal clothing and training in hot ambient conditions are equally effective methods of heat acclimation. J Sci Med Sport. 24(8):763-767, 2021.

Check out the video by clicking below!

Full Transcript

A specific plan of gradually adapting to heat is one of the best things that athletes can do to prepare for competing in hot environments. But what if you don’t have access to heat facilities?

In today’s episode, we’ll explore a study testing heat adaptation through training indoors and wearing heavy clothing. Can it provide the same benefits as training in a hot environment?

Exercising in the heat can be very challenging, with much lower performance compared to cooler temperatures. Indeed, lower performance is already seen in typical room temperatures that most of us would rate as comfortable when at rest. The best thing that athletes can do to prepare for hot weather competitions is to heat adapt through gradually exposing themselves to exercise in the heat over 2 weeks or more. Classic adaptations include lower heart rates and core temperatures at both rest and during exercise, increased sweating rates, decreased thermal and exercise discomfort, and ultimately greater power output. The challenge though is that not everyone has access to a heat chamber or the ability to go to hot-weather training camps. However, most of us have extra clothing that we can pile on while training. Can the use of clothing adapt us as well as heat training?

A Scandinavian group tested this question with 34 trained competitive cyclists split into 3 groups. The HEAT group performed traditional heat training on an indoor bike, with 10 days of 50 min at an easy effort in a hot environment. The SUIT group did the same protocol, but in 19.5°C temperatures but wearing multiple layers of winter and impermeable clothing. The final group did the same training as the SUIT group, but added 30 minutes of hot water immersion afterwards to extend the heat stimulus. Importantly, the very easy effort meant that any changes over time were likely not due to a training stimulus but to heat adaptation instead.

Before and after the 10 days of training, testing was performed in 35°C. First, the cyclists rode for 15 minutes at a steady submaximal effort, then they rode as hard as they could for 30 minutes. As expected, resting and exercise core temperatures and heart rates were lower after the 15 min submax ride, showing that heat adaptation did occur. Interestingly, the total amount of hemoglobin – the molecule for carrying oxygen in the blood – also increased. This was seen before by the same group in a very long heat training study of 5+ weeks, but has not been seen before with the more typical 2 week training study. In the time trial test, all three groups improved average power significantly and by about 9% after 10 days. Importantly, the improvement was the same with the SUIT and SUIT+ hot water group compared to the traditional HEAT group.

So where does this leave us in terms of ways to heat adapt? The big insight from this study is that, in terms of both physiological and performance responses, training with heavy clothing may heat adapt us as well as with traditional exercise in hot environments. This makes intuitive sense in that the main goal of heat adaptation is to raise body temperature, and our body is agnostic about how that’s done. One caveat is that this finding may be specific to indoor training, as riding outdoors generate a lot more wind exposure and convective cooling, which may limit the heat stimulus even with heavy clothing on. Finally, it’s unclear why the extra hot water immersion had no extra benefit, as it has shown to be beneficial in several studies and it theoretically would have had the greatest overall thermal stimulus. One possibility is the highly trained nature of these participants, such that their ceiling for improvement has already maxxed out.

Dr. Stephen Cheung in the lab with a ‘subject’ (his wife Debbie suffering for science)



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