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I don’t want to jinx anything, but I think it’s finally safe to put away the balaclava. 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 advantages. Here are five things to know about the science of summer exercise:

You get used to it

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

This process of heat acclimatization starts after as few as two hot-weather workouts, and maxes out after about two weeks. But you can’t just lie around on your deck chair waiting to acclimatize: The adaptations happen when you elevate your core temperature, so you have to exercise in the heat to get the benefits.

It 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 bolsters an even stronger claim: heat training makes you fitter even if you’re competing in cool 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 per cent after five weeks of training in hot conditions, compared to a control group doing the same workouts in cool conditions. Hemoglobin is the protein in red blood cells that ferries oxygen to your muscles, so this increase translated to better cycling performance regardless of the temperature.

Movement matters

Another recent study, this one from researchers in Spain, crunched eight years of training and race 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 topped 25 C.

In contrast, a similar study of runners found that performance started to tail off 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.

Beware the sun

It’s not just the temperature, it’s the humidity, right? That’s true, but it’s also the sun. When you step out of the shade into full sun, you can feel the difference. The air itself isn’t warmer; instead, you’re being heated directly by electromagnetic radiation from the sun, much as a microwave oven cooks food without warming the air.

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

The takeaway: wear a hat, opt for morning or evening workouts, and consider cloud cover in addition to temperature and humidity when you’re checking the weather forecast.

Perception is reality

Perhaps the most fascinating line of heat-related research in the past decade is the role of perception. Athletes give up sooner if the thermometer is rigged to show a falsely high temperature, or if they’re fitted with a heat pad that makes them feel slightly warmer without actually increasing their body temperature.

That doesn’t mean that the physiological consequences of hot-weather workouts – dehydration, rising core temperature, and so on – aren’t real. But your brain will start applying the brakes well 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 off if you’re feeling dizziness or nausea, for example. But in most circumstances, the main consequence of summer exercise is that you’ll get hot and sweaty. You may not love it, but it beats frostbite.

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

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