Five things to know about hot-weather workouts

I don’t want to curse anything, but I think it’s finally safe to put the balaclava away. For the next few months, the big challenge during outdoor exercise will be staying cool.

Hot weather workouts can be challenging, but they also have some surprising benefits. Here are five things to know about the science of summer exercise:

You get used to it

It’s not wishful thinking: The same 20-degree heat that felt like a godsend in May will seem downright brisk in August. Regular exercise in hot conditions triggers a series of physiological changes that keep you cooler: Your sweat glands fire earlier, your blood volume increases, and your heart rate stays lower.

This process of acclimatization to heat begins after just two hot weather workoutsand reaches its maximum after about two weeks. But you can’t just lie on your lounger waiting to acclimatize: Adaptations happen when your core temperature rises, so you have to exercise in the heat to reap the benefits.

makes you fitter

Athletes preparing for hot-weather competitions like last summer’s Tokyo Olympics have long known that they need to train in the heat. But a new study from researchers in Norway reinforces an even stronger claim: training in the heat makes you fitter even if you’re competing in cold conditions.

The study, published last month in the journal Medicine and Science in Sports & Exercise, found that cyclists increased their hemoglobin levels by 2.5 percent after five weeks of training in hot conditions, compared to a group of control that did the same workouts in cold conditions. Hemoglobin is the protein in red blood cells that carries oxygen to the muscles, so this increase translated into better cycling performance regardless of temperature.

movement matters

Another recent study, this from researchers in Spain, analyzed eight years of training and racing data from 74 professional cyclists to explore the effect of temperature on their power output. Surprisingly, they found that performance only dropped noticeably when the thermometer went above 25°C.

Unlike, a similar study of runners found that performance began to decline above 18 C. The difference? Cyclists generate their own cooling wind. Runners do too, but at lower speeds. Whichever option you choose, think of the findings as an incentive to go faster.

Watch out for the sun

It’s not just the temperature, it’s the humidity, right? That is true, but it is also the sun. When you step out of the shade into full sun, you can feel the difference. The air itself is not warmer; instead, the sun’s electromagnetic radiation heats it directly, in the same way that a microwave oven cooks food without heating the air.

A 2016 study by researchers in Japan had volunteers cycle to exhaustion in 30C heat under artificial solar lamps corresponding to varying degrees of cloud cover. Even with constant temperature and humidity, the volunteers lasted only half as long in full sun as they did in cloudy conditions.

The bottom line: Wear a hat, opt for morning or evening workouts, and consider cloud cover in addition to temperature and humidity when checking the weather forecast.

perception is reality

Perhaps the most fascinating line of research related to heat in the last decade is the role of perception. Athletes give up sooner if the the thermometer is rigged to display a falsely high temperature, or if they are equipped with a heating pad that makes them feel a bit warmer without actually increasing their body temperature.

That’s not to say that the physiological consequences of hot-weather workouts (dehydration, increased core temperature, etc.) aren’t real. But your brain will start applying the brakes long before you’re in danger.

It’s important to treat hot weather with respect: drink when you’re thirsty, seek shade when possible, and back away if you feel dizzy or nauseated, for example. But under most circumstances, the main consequence of summer exercise is that you get hot and sweaty. You may not love it, but it’s better than freezing.

Alex Hutchinson is the author of Enduring: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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