Use Summer Heat to Get Stronger and Faster

Most people wilt in the heat. Here are 4 ways to use it for better health.

Savoring some shade on the hottest day of my 40-day desert hike.

Post summary

• Heatwaves are rolling across the country.

• If you’re active, you may wonder whether exercising in the heat is good for you or just miserable.

• Heat can significantly boost our health and fitness. But if we overdo it, we can do more harm than good.

• This post explains the benefits of the heat and gives us four simple rules to ensure we’ll get the upside without burning out.

Housekeeping

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The post

Over the weekend, I came across two headlines:

• “It’s About to Get Brutally Hot in New York City”

• “Midwest Cities Bake as Heat Wave Blankets the Central U.S.”

I read them while exercising in my garage gym, which was 101 degrees.

Welcome to the great American furnace.

I’ve always wondered about working out in the heat …

On one hand, some studies suggest heat can boost our health and performance. On the other hand, marathon times tank in high temperatures¹, and ER visits spike during heatwaves.

So which is it? Is the heat the good for us? Bad? Or is it more like the Switzerland of environmental exposure: neutral?

To answer these questions, I spoke with Chris Minson, a professor at the University of Oregon and one of the world’s leading experts on how the human body adapts to environmental extremes.

Minson began his work during the Gulf War, where soldiers were facing 110 to 120-degree days.

“To be honest, the US was not really prepared to fight in the heat,” Minson told me. “I was the guy who was brought in as a grad student to assist with what were called Heat Stream Countermeasures.”

He’s studied heat and whether it can improve human health and performance ever since. Think of him as the heat whisperer.

Let’s roll …

Health benefits of heat

• Section summary: Controlled heat exposure can improve heart and metabolic health, but only when done right.

Heart disease is what’s most likely to kill us—and heat might help reduce our risk.

“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 see metabolic health improve.”

For example, in one study,² Minson had young, sedentary people sit 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.”

In another study, Minson 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 the people are only sitting in the heat.

Other research backs this up. A famous study³ from Finland found that men who used the sauna 4 to 7 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 between 176 to 212 degrees.

Of course, people who use a sauna at least four times a week are likely more health conscious in many other ways (e.g., saunas are often in gyms). So there’s some noise.

But heat in reasonable and controlled doses seems to mimic light cardiovascular exercise. It increases cardiac output (the amount of blood the heart pumps per minute) and stroke volume (the amount of blood pumped per beat).

It may also elevate heat shock proteins. These are stress response proteins involved in repair, recovery, and adaptation.

• Caveat: These benefits are observed in controlled studies, where researchers keep a watchful eye. When a heatwave surprises vulnerable populations like older adults, people with chronic illnesses, and kids, bad things can happen. OSHA estimates that 11,000 Americans have died from heat-related causes since 1979. The practical takeaway is to use heat tactically.

Can heat replace exercise?

• Section summary: Controlled heat exposure shouldn’t replace exercise but it might be particularly beneficial for three groups.

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

That said, there are three types of exercisers for whom heat exposure alone (like a sauna or sitting outside on a really hot day) can be particularly beneficial:

• 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.

This brings us to us: Two Percent readers who like to exercise outdoors.

Should we work out in the heat?

• Section summary: Exercising in the heat seems to improve health and performance in some conditions—but you have to be careful with it.

Minson ran a study⁴ with two groups of cyclists. He measured their race performance then had each group do ten 90-minute training sessions.

• Group one trained in a 55-degree room.

• Group two trained in a 104-degree room.

After the training, both groups raced in both hot and cold conditions.

Group one saw no difference, but the heat group improved their race performance by:

• 5 percent in cooler temperatures.

• 8 percent in hotter temperatures.

The heat training also boosted a few other performance marker, like VO2 max and time trial performance.

Another recent study 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.

Other studies suggest that using the sauna after a workout is beneficial.

That study⁵ 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.”

Be careful

Minson doesn’t give elite athletes free rein to train in the heat. It only delivers benefits if we don’t become dehydrated, too tired, or too hot.

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

A case study

To understand how Minson uses the heat to improve his athletes, consider this case study.

Let’s say the Oregon track team has a meet in Texas, where it might be 100 degrees. He’ll put athletes in saunas so their bodies acclimate, 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 blood 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.”

We’ve all probably experienced this.

Each spring, when my garage gym first hits 90, I feel like death, and my workouts suck. But after a couple of weeks, the heat becomes manageable, and I’m back to good.

4 ways to benefit from the heat

Just like cooking food, too much heat for too long burns. But the right amount of heat for an appropriate time can create something great.

Here’s how to exercise in the heat to get benefits:

1) Ease in and aim for a 7

Don’t jump into hot workouts. If you do too much, too soon, you’ll do more harm than good.

Minson recommends a 10-day onramp.

• Do some moderate exercise, like a fast walk or slow run, ruck, or ride outside in the heat.

• Use a subject scale that goes from 0 (totally comfortable) to 10 (feeling miserably hot). Aim for a 7 out of 10. You should feel “pretty hot” and be sweating, but not miserable.

• Once you reach above a 7, stop exercising.

• Do that five days in a row, rest two days, then repeat for another five days.

Using a sauna or hot tub can also you onramp.

Bring yourself to a point where you feel like a 7. Sit for about 15 minutes a few days a week for two weeks. Minson said that will help your body adapt so your first workouts in the heat don’t burn you out.

Acclimating in a sauna can be smart in two conditions:

• If you had a marathon or triathlon in a place hotter than your hometown.

• If you’re traveling somewhere hotter this summer (the method would prevent you from sweating too much and feeling too hot).

2) Drink often

“I want people hydrating” 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.”

Becoming dehydrated can cancel out any benefits of the heat and become dangerous.

Bring water. Drink normally. Here’s an easy way to ensure you replace the water you sweat out:

• Weigh yourself before and after your workout.

• If you’re lighter, drink that amount of water.

• For example, if you were a pound lighter, you’d drink 16 ounces of water. That’ll also help you figure out how much to drink next time.

3) Break the “humidity bubble”

If sweat is dripping off of you, it’s basically just wasted energy. Sweat only cools you when it evaporates from your skin.

It creates what Minson calls a “humidity bubble” and increases the odds you’ll overheat.

Create airflow so your sweat can do its job. This can be challenging if you live in a humid environment and are exercising outdoors. But if you have access to a fan, use it. Definitely put a fan in your garage gym.

4) Don’t overcook

If you start a hot event like a hike or race too fast, you can spike your core temperature and crash early.

Minson calls this “overcooking it.” Once you’re overcooked, you become excessively fatigued and are basically done for. It’s our body’s defense mechanism kicking in to help us avoid injuring ourselves.

Ease in and save your hardest effort for the finish line.

Have fun, don't die, bake but don’t burn,

-Michael

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1. This graph shows average finishing times from various marathons. In short: Finishing times get slower as the temperature rises.

2. Brunt, V.E., Howard, M.J., Francisco, M.A., Ely, B.R. and Minson, C.T. (2016), Passive heat therapy improves endothelial function, arterial stiffness and blood pressure in sedentary humans. J Physiol, 594: 5329-5342.

3. Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Intern Med. 2015 Apr;175(4):542-8. doi: 10.1001/jamainternmed.2014.8187. PMID: 25705824.

4. Lorenzo S, Halliwill JR, Sawka MN, Minson CT. Heat acclimation improves exercise performance. J Appl Physiol (1985). 2010 Oct;109(4):1140-7. doi: 10.1152/japplphysiol.00495.2010.

5. Scoon, Guy & Hopkins, William & Mayhew, Simon & Cotter, James. (2007). Effect of post-exercise sauna bathing on the endurance performance of competitive male runners. Journal of science and medicine in sport / Sports Medicine Australia. 10. 259-62. 10.1016/j.jsams.2006.06.009.