Ice baths kill gains. Does the sauna do the opposite? [New research]

Chapters:

00:00 Intro

00:17 Inflammation

00:29 Cold vs. Heat Therapy

00:58 A Thermo-regulatory Response

01:20 Effects on Cardiovascular System

01:37 Too good to be true?

02:26 Recovery?

03:03 Effects on Health

03:48 Placebo?

04:22 Conclusion

Transcript:

Despite their influencer led popularity, ice bath, cold plunges and other forms of cryotherapy have been shown quite conclusively in research to be a net negative for muscle growth and strength development. They suppress inflammation and slow down chemical reactions.

While lay individuals often think of inflammation as a bad, it’s actually an integral part of the muscle repair process, so suppressing it has negative consequences for recovery and ultimately, muscular adaptations. It stands to reason, then, that if cold plunges and all these forms of cold therapy are bad, is heat therapy actually a positive? The answer seems to be yes, according to a preprinted meta analysis of six studies. The Bayesian analysis found the 90% probability that heat favored muscle growth. However, the effect size was very small.

Mechanistically, it’s well established that heat improves the speed of chemical reactions. It also speeds up blood flow and perhaps most importantly, very intense heat activates heat shock proteins. Mild hyperthermia, basically overheating of the body, triggers a thermo-regulatory response that is not unlike exercise. It is hormetic. Hormetic basically means – what doesn’t kill you makes you stronger. So mild overheating triggers adaptive responses in the body that have some effects, somewhat like exercise. And they are good for you in small amounts as long as the body can recover from this.

A 2018 systematic review concluded that sauna bathing has positive effects on the vascular system. Moreover, a 2021 meta analysis found that regular sauna bathing resulted in a clinically meaningful reduction in blood pressure, namely 4mmHg.

If this sounds too good to be true and you think you can have a nice relaxing sauna after your workouts, and get better gains and better health – it is. You need to suffer. Significant heat stress is required to actually induce the significant health benefits. For example, a 2026 meta analysis found that regular hot baths up to 41°C did not significantly improve the vascular system. The only somewhat meaningful effect was a reduction in heart rate.

So relaxing saunas are not the fountain of youth. They are also not the ticket to the Olympia. As I said, the effect size was very small. To quote the researchers, they named it: “some evidence of a small effect favoring heat therapy” and the credible interval extended below zero, which is a statistical way of saying the actual effect might still very well be zero, Moreover, for strength development, the effect size was almost exactly zero.

The potential extra gains are also not free, in the sense that the significant heat stress that is required to trigger these adaptations might actually delay recovery. In one of the few studies on elite athletes with a proper placebo control swimming performance the day after the sauna was actually impaired.

Many people overestimate how important it is to study trained individuals. Untrained individuals often have the same effects, just to a different degree than trained individuals. However, in the case of the sauna, this might not be true because if you’re already well adapted as an athlete and your vascular system already has a certain level of adaptation, then sauna bathing might not be enough stimulus anymore to trigger further adaptations.

Finally, from a health point of view, sauna bathing is also not completely free from side effects. It’s generally considered quite safe, and it’s very self-limiting in the sense that most people will not go to the extreme lengths required to actually do damage. However, it does reduce fertility. One study concluded sauna use results in a strong impairment of sperm count and motility, and that was with just two weekly sessions in a Finnish sauna. The reason is that heat is well established to be toxic to sperm. This is quite literally why men’s balls hang outside of their body. It’s a little bit cooler.

Fortunately, sauna bathing is not strong enough to do permanent damage to the testes. When you remove the heat stress sperm quality gradually goes back up to normal levels. So the reduction in sperm quality is mostly relevant for people that are right now trying to have kids.

A final significant limitation of the research on heat therapy is that it’s very difficult to have a proper placebo control. You can’t make someone unaware that they’re sitting in a sauna, and many people have positive associations with the sauna, even if it’s just relaxing or health benefits, and this can result in positive expectation effects, i.e. the placebo effect, which makes it very difficult to say if it’s just the placebo effect, or actually the heat stress that triggers these adaptations.

However, considering we have mechanistic evidence linking the heat stress and the heat shock proteins to the vascular adaptations, I think it’s hard to make this a case for a full placebo effect.

Overall, after reviewing all of the available evidence, the conclusion I came to in my PT Course is as follows: If you enjoy sauna bathing or heat therapy, by all means do it. You probably get some additional health benefits and it might even slightly improve your gains. However, if you don’t enjoy it, the cost benefit is very poor. For the time, suffering, and often money that’s involved in going to the sauna, you are much better off exercising.

If you like no nonsense, evidence based reviews of popular fitness topics, you’ll probably also like this video or check out my PT course. See you next time!