Post summary

• Heat exposure therapies like sauna are rising in popularity, but whether they're worthwhile depends on who you are.
• Heat therapy seems to offer some strong health benefits that mimic (but don't trump) exercise.
• Heat therapy's impacts on fitness aren't as impactful, but may be worthwhile for experimenters and elite athletes.
• We'll help you determine whether heat exposure is worth it and the best way to do it.

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Podcast version of this post

Today's post

My garage gym hit its first day over 80 degrees last week. It'll reach over 110 at the height of summer.

I have a love hate-relationship with my furnace-like garage gym. Summer workouts feel harder in the moment—but also purifying. And because the workouts feel harder, they're also more rewarding when I'm done.

Yet I've always wondered if training in the heat delivers any additional, legitimate benefits—or whether it's just harder for the sake of feeling harder.

Plus, saunas and heat therapy are becoming more popular. Is heat exposure and heat therapy legit?

To find out, I called one of the world's foremost physiologists, Chris Minson. Minson is a professor at the University of Oregon who studies how our bodies change and adapt to environmental extremes.

Minson began his work during the Gulf War. "To be honest, the US was not really prepared to fight in the heat," Minson told me. "And so I was literally the guy who was brought in as a grad student to assist with what were called Heat Stream Countermeasures."

He's continued the work and is now a leading mind on whether heat can improve human health and performance.

Let's roll ...

Health benefits of heat

• Section summary: Heat exposure seems to improve heart health.

"In most of the studies, we generally see that most peoples' biomarkers of cardiovascular and metabolic health get better (after heat exposure)," Minson told me. "We see reductions in blood pressure and arterial stiffness. We'll see their metabolic health improve."

For example, this study took a group of young, sedentary people. The experimental group sat in a 105-degree bath for 60 minutes. This happened four to five times a week for eight weeks.

Minson wrote: "Heat therapy increased flow-mediated dilatation, reduced arterial stiffness, reduced mean arterial and diastolic blood pressure, and reduced carotid intima media thickness, with changes all on par or greater than what is typically observed in sedentary subjects with exercise training."

Another of Minson's studies took obese women and exposed them to the heat. He told me:

"We saw their glucose levels drop, their A1C (a marker for diabetes) drop, and their insulin sensitivity increase.
It's very similar to what you might expect with some of the benefits of exercise. But we've separated it so some people aren't exercising and are only doing the heat stress."

A famous study from Finland, where saunas are popular, found that men who used the sauna 4 to 7 times a week were less likely to have heart disease or die over the ~20-year study period.

And not, like, mildly less likely to die. They were really less likely to die.

The group who used the sauna at least 4 times a week saw a 40 percent reduced risk of death compared to those who used it once. A group who used it 2 to 3 times per week saw a 24 percent drop in their risk. These saunas were usually 176 to 212 degrees.

Of course, people who can sauna at least four times a week are probably more health conscious in a lot of other ways. So there's some noise. But 40 percent is 40 percent.

Sauna seems to work for various reasons, many of which mimic light cardiovascular exercise. Which raises a question ...

Can heat therapy replace exercise?

• Section summary: Heat exposure shouldn't replace exercise but might be particularly beneficial for three groups.

Minson told me, "The question I get the most is 'this heat therapy sounds so healthy. Does this mean I don't have to exercise?' And my answer is, oh God, no. If you do just one healthy thing, make it exercise."

TL;DR: If you feel like you don't exercise enough, you should fix that issue before you devote time to heat therapy.

There are three types of exercisers for whom the sauna could be particularly good:

• People who will never exercise: "Heat therapy isn't a replacement for exercise, but it might be something exercise-averse people will actually do that would give them some benefits," said Minson.
• People who want more from their exercise. "Heat therapy might extend the benefits of exercise," said Minson. (More on that below).
• People who have exercise limitations. For example, injury patients. "Heat therapy could help these people if they can't get the full benefits of exercise," said Minson.

Fitness benefits of heat

• Section summary: Heat exposure seems to improve performance in some conditions—but you have to be careful with it.

In one study, Minson got two groups of trained cyclists and measured their race performance. Then each group did ten 90-minute training sessions.

• The first group did their training sessions in a room that was 55 degrees.
• The second group did their training sessions in a room that was 104 degrees.

Minson then remeasured their race performance in a hot environment and cool environment.

The results: Heat exposure improved the heat group's race performance by 5% when they raced in cool conditions and 8% when they raced the heat. It also boosted a few other performance markers.

Other studies have found using the sauna after a workout could be beneficial.

That study found that spending about 30 minutes in the sauna after a 15-minute all-out running workout "produced a worthwhile enhancement of endurance running performance, probably by increasing blood volume."

But Minson doesn't give elite athletes free rein to train in the heat.

"I'm very careful with elite athletes," he said. "We're trying to balance all their training. If an athlete uses heat haphazardly it can destroy all the training they've done the few years leading up the competition."

He's careful and tactical.

For example, let's say the Oregon track team has a meet in Texas, where it might be 100 degrees.

He'll have the team use his heating chambers in the weeks leading up to the track meet. Their bodies will adapt to that heat, leaving them better off when they go from the mild temperatures of Oregon to the furnace of Texas.

Minson told me, "Then the athletes can run at a given pace and not have their core temperature go up as high. Their blow flow and sweating won't have to go as high because they'll be able to keep their body temperature lower. All those have performance benefits."

Minson mentioned a new study. It found that training in the heat for five weeks led to increases in red blood cell mass. "If you can increase red blood cell mass, then most endurance athletes will be able to run faster, bike faster, etc," said Minson.

And you can do the same.

• If you had a marathon or triathlon in a place hotter than your hometown, you could spend time in the sauna to prepare.
• If you're traveling somewhere hotter this summer, you could spend some time in the sauna beforehand so you don't sweat as much and feel as hot during your trip.

I've seen this in myself.

A funny thing happens to me in the springtime when I train in my garage. The first days over 80 feel like death. It sucks.

But after a few weeks, the heat becomes manageable. Soon enough, the temperatures reach 110 and it feels hot but not soul crushing.

How to start

Here's a five-step guide to leverage the power of the heat. On Wednesday, I'll give you details on how I use this.

1) Decide if you even want to start

We could do so many things daily to improve our health.

Living well requires introspecting to figure out what practices will give you the most benefits for the time and personality you have.

If you barely find time to exercise, you should probably get that in order before you worry about heat exposure.

The heat exposure research is compelling. But remember that people meet their health goals and turn 90 daily without ever stepping in a sauna.

2) Ease in

Let's say you do decide to start using a sauna. Maybe your gym has one and it's an easy way to end a workout. Or you want to install one at home.

During your first sessions, bring yourself to a point where you feel fairly warm but not hot. Then sit for about 15 minutes. Minson said that will help your body adapt and avoid any possibly downsides.

3) Bake—don't burn

Once you've completed a few ease-in rounds, raise the temperature to a point where you feel hot. Most studies use temperatures between 180 and 210 degrees.

"I want you to feel hot, but not miserably hot," said Minson. "Then stay in there for around 15 to 20 minutes."

4) Drink as you bake

"I want people hydrating while they're in there," said Minson. "There's some debate in the literature about whether your response is different if you're hydrating, but I don't think much about that." The consequences of dehydrating and then not recovering aren't worth it.

Bring water. Drink normally.

To ensure that you replace the water you sweat out, you can weigh yourself before and after. If you're a pound lighter, then drink 16 ounces of water.

5) Use the time well

We're all time-crunched. Use your sauna time to do other things. For example, read or meditate.

My friend Rob MacDonald brings a cold pack into the sauna. He sets his phone on the cold pack so it doesn't overheat—then he catches up on emails.

Have fun, don't die, bake,

-Michael

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