Can Heat Boost Muscle Growth?

Can Heat Boost Muscle Growth?

The sauna is one of the most misunderstood tools in the world of fitness. Generations of misguided-but-well-intentioned fans have sworn that sweating it out in the sauna burns fat (spoiler alert: it doesn’t).

But it does build muscle.

A fast-growing mountain of research is finding that turning up the heat causes a biological reaction that stimulates muscle-building and repair. Here’s what you need to know to take full anabolic advantage.


The Science

According to researchers at Korea University in Seoul, raising muscle temperature post-workout results in more muscle mass and a natural boost in growth hormone levels. To see optimal results, the study found athletes needed to expose their muscles three times a week to a heat source that raises the temperature of their muscles by 4 degrees Celsius (that’s 40 degrees Fahrenheit hotter for us ‘Mericans) – perfect sauna temperature territory.

Not to worry, you won’t get cooked running an insane 140 degree fever. Because we’re dealing with muscles just beneath the skin, muscle temperature elevates much more quickly than your core temperature. So while your muscles will heat up in the hot air of the sauna, your core temp won’t rise nearly as dramatically.  

Japanese sports scientists documented a similar experiment in the Journal of Physiological Sciences and arrived at the same conclusion – heat, following training, made muscles grow more and repair themselves faster.  

The Japanese study went further, performing muscle biopsies of the athletes’ quads to investigate why heating muscle had an anabolic effect.   

When they examined the muscle tissue, the researchers found that heating muscles after strength training boosted the activity of heat-shock proteins and growth hormone, as well as Akt, mTOR, S6 and 4E-BP1 – key anabolic regulator molecules which initiate growth reactions in muscle cells.

They concluded that heating muscles during the post-workout window directly effected “the regulation of mTOR signaling molecules and the rate of protein synthesis in human skeletal muscle".



One final study, published in the European Journal of Applied Physiology, drives home the point: researchers exposed their experimental groups’ muscles to heat treatments 4 times a week for 10 weeks.

At the end of the 10 weeks, MRI imaging found a 6% increase in muscle size in the heat treatment group – while the gains alone are impressive, the results become flat out remarkable considering participants were not allowed to do any strength training.

For a 200 lbs. man, a 6% increase works out to 12 lbs. of muscle-gain, in just ten weeks. Without lifting.  

Do you even heat, bro?


What to Do

+ Try to hit the sauna at least 3 times per week, immediately after workouts.

+ Shoot for sauna stays of around 10-20 minutes.

+ If the sauna has seats or benches that are at different heights, aim high. It’s brutally hot up there, but you’ll only be in for a bit. Saunas are as much as 30 degrees cooler at the floor, and reach their max temperatures at the ceiling, so where you are in that spectrum of height matters tremendously.

+ If possible, lay down on the bench, so that your entire body is at the same elevation and getting equal heat. If you’re sitting up, your head will be getting far more heat than the rest of you – and we’re not trying to make your head grow.

+ If it’s crowded, obviously you may have to sit up, but it’s worth giving laying down a shot if you never have -- many people who hate how the sauna makes them feel find that it’s suddenly tolerable when they’re laying down, and their head is no longer roasting 20 degrees hotter than their body.   


What NOT to Do

- Don’t stay in the sauna longer than 20 minutes at a time. Put bluntly: the testicles don’t like to be too warm for too long. If your balls get cooked, they’ll punish you by reducing the amount of testosterone they produce, which will dampen the muscle-building effect we’re going for. Get in and get out.

- Don’t wear layers in the sauna. Sweatshirts, beanies, etc. are actually counterproductive in this case. They’ll make you sweat more, but in the short 10 to 20 minutes you’re in there, wearing extra layers only insulates you -- raising your core temperature more than your surface/muscle temperature. Layers keep the hot air of the sauna off your skin, while keeping more of your own heat in, and that’s not the goal.

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