No need to demonize the summer heat.

By Mellanie Perez
August 03, 2020
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As soon as temperatures hit high 80s, outdoor fitness enthusiasts scurry indoors and trade asphalt for treadmills—and we can’t blame them. Every person’s idea of perfect outside conditions vary, but they likely involve low humidity and cool temperatures (nothing like our current summer). But just because we can’t have spring weather all the time doesn’t mean we can’t take advantage of the summer heat and stay on track to achieve fitness goals.

Enter, heat training: using heat to boost your exercise performance and overall health. It's great news for all runners and fitness enthusiasts who have taken to the parks more frequently due to COVID-19—but it takes more than just laying poolside during recovery on a hot day. Here’s what you need to know about what heat training can do for your body; and with the right approach, how it can make you stronger and fitter than ever, post-quarantine.

Benefits of heat training

Heat training has been demonstrated in various studies to improve aerobic exercise performance, that means exercise such as running, cycling, rowing, etc. Heat acclimation triggers a series of physiological adaptations that can boost your performance. If you’re an elite athlete, the most notable of these is increased production of hemoglobin—the key protein in your red blood cells that carries oxygen to your body’s major organs and tissues—which has a direct effect on your overall endurance. 

A recent study published in Experimental Physiology found that training for 5 hours a week for 5 weeks in 100-degree heat boosted the hemoglobin levels in male elite cyclists by 4-5 percent, boosting overall oxygen intake. “By increasing your hemoglobin concentration, you’re enhancing the oxygen-carrying capacity of your blood, and you’re improving upon that potential weak link for the endurance athlete,” Robert Mazzeo, PhD, associate professor of Integrative Physiology at University of Colorado Boulder, tells Health. Keep in mind, though, that this study was done in elite athletes; for recreational athletes, it’s not likely that the limiting factor in your performance is your max cardiac output and oxygen delivery systems, so the hemoglobin benefit isn’t likely to be dramatic.

The next most dramatic change after just a few days of heat training is a boost— almost 20 percent—of plasma volume in your veins (just FYI: plasma is, essentially, the liquid portion of blood). And an increase in plasma volume may make even recreational athletes better at thermoregulation, or the body's ability to maintain a certain body temperature," says Mazzeo.

In the simplest of terms, by getting acclimated to heat, your body gets better at sweating and cooling itself down. When you’re training, you want a certain amount of blood and oxygen to go to your muscles, but if you’re training in the heat, you have to divert some of that blood flow to the skin for to cool you down and help your body maintain its core temperature, which causes plasma production to go into overdrive. Essentially, "increasing your plasma buy-in helps you thermoregulate by helping the blood go into the skin, keeping it as cool as possible, given the disruption in its homeostasis,” says Mazzeo.

The benefits of increased plasma volume goes beyond helping your body to stay cool, too–more plasma in your body means more blood can be sent to cool your skin without compromising the supply of oxygen being carried to your muscles, giving you the ability to last longer, even when you take your workouts back inside. "Increases in plasma volume from heat acclimatization may lead to better endurance and longer lactate threshold when returning to cooler or normal training temperatures,” Roger Adams, PhD, ACE-CPT and owner of eatrightfitness in Oklahoma, tells Health. The way higher plasma levels directly affect endurance is still debated, but most scientists agree that the extra plasma also has the effect of diluting the concentration of red blood cells in your blood, which in turns triggers the production of more hemoglobin-rich red blood cells, making it easier for your muscle to obtain oxygen. 

Remember, though: While a lot of these benefits sound promising, it's important to keep in mind that there are limitations to most research done around the pros of heat training—primarily that the majority of studies focus solely on elite athletes, without looking into the effects of heat training on the average recreational athlete or gym goer. That means, though you may reap some benefits from training in hotter temperatures, they may not be as pronounced as those reaped from professional or elite athletes.

How to work out in the heat safely

Heat training is no joke, and it's not something to be taken lightly—primarily because it's just not your body's go-to for training purposes. "Ideal training temperature is, general speaking, about 68-72 degrees,” says Ryan. “It is warm enough to keep the muscles warm, but not too warm to where it overly taxes your system to cool down.” Plus, Adams adds that the ideal running temperature is actually in the 40s.

That means you probably shouldn't start training in 90-degree weather every day without a little preparation. Adams says it takes about 10-15 days for your body to acclimate to the heat, so take it slow, follow a program, and be smart about the time of day you choose to get outside. It's also wise to keep in mind the risks that come with hot summer weather—heat stroke, sunburn, and dehydration to name a few—which makes it even more important to focus on safe heat and exercise practices. 

“Heat, plus humidity, plus direct sunlight is a triple-threat combination, so keep that in mind, and try to schedule your workouts accordingly,” Chris Ryan, CSCS, NSCA-certified personal trainer on NBC’s Strong, tells Health. “Do the harder portions earlier in the day, and lighter portions in the hotter parts of the day.” The fitter you are, the better your body can tolerate exercise in the heat, so if you’re starting to heat train for the first time in the dead of summer, do a shorter and slower-that-normal workout. You want to make sure you don’t go too fast trying to match your spring pace or intensity right when you’re starting out. On each subsequent hoy day go a little farther and a little faster. 

It's also in your best interest to stay properly hydrated, Ryan says—and you have to start even before you hit the pavement. "It starts 24-48 hours before a hot workout or competition. Electrolytes are key to ingest every hour of activity, as well as moderate salt intake.” Adams even has his athletes weigh themselves before and after they train, and then for every pound they have lost, they need to consume 2 cups of water. “I have my athletes consume 16-ounces or more of water or hydration solution right before training and then keep consuming around 4 ounces every 20 minutes or so,” he says

And then, of course, there’s the element of proper clothing. “Proper clothing that allows the sweat to wick off is a plus, as clothing that traps heat and sweat may increase your chances of heat-related issues and lessen your body’s ability to cool off effectively.” And naturally, don’t forget to apply a sunscreen regularly with at least SPF 30 to protect from damaging sun rays. 

So while you may not willingly choose to go run a few miles outside in the middle of summer under typical circumstances, the training technique may actually up your performance—just make sure to do it slowly, safely, and to listen to your body even more when out under the hot sun.

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