Use this drink tip to stay cool on hot, humid runs

how to stay cool on hot runs

Staying adequately hydrated is vital to training well in the summer. If bracingly cold drinks are your thing before or during a brutally warm run, studies have shown that, compared to the same amount of warmer drinks, these beverages might allow you to go harder or longer.

On the surface this might seem like like no-duh research, but it comes with a big caveat: this trick appears to give you the most benefit only in hot, humid weather where you end up sweating buckets, according to a recent Gatorade Sports Science Institute article by Ollie Jay and Nathan Morris of the University of Sydney in Australia.

Where you might not get much of a boost is when you are drinking cold drinks before and during a run on a hot, dry, windy day. Doing so may cause your body to retain more heat, meaning that you might have to slow or even stop sooner than you anticipated.

What cold drinks do inside you

The discrepancy between weather conditions stems from what happens after you drink cold beverages. (The article uses a threshold of 10 degrees celcius or cooler. Most of the research has used much colder drinks. By way of comparison, the temperature inside a typical refrigerator is between 1.6 and 4.4 degrees.) Your body will warm the liquid, resulting in some heat loss.

But, say Jay and Morris, two of the world’s top experts on exercising in the heat, colder drinks consumed during exercise don’t reliably lower your body’s core temperature more than warmer drinks. Instead, the key mechanism appears to be that thermoreceptors in your stomach reduce sweat production on your skin when you down a really cold drink. And that’s a good thing only some of the time.

Related: 6 of the best sunscreens for runners 

The purpose of sweat, after all, is to cool you, not dehydrate you. Evaporative heat loss occurs as air moves over your sweaty skin. Sweating leads to performance-harming levels of dehydration only when you don’t—or can’t—make up those sweat losses quickly enough. In less extreme conditions, when it’s possible to stay adequately hydrated, more sweating should mean greater heat loss, resulting in being able to maintain a higher work load because, in a sense, your internal engine isn’t overheating as you crank out more miles.

Now, consider two scenarios. In one, you’re running on a hot but dry and windy day. The sweat you produce will help cool you thanks to the dry air (which can absorb the moisture and keep your from being a sweaty mess) and the wind. But in this case, if you lower your sweat production by drinking cold beverages, it will mean you’ll retain more heat—and eventually have to slow down—because you’re not sweating enough.

In the second scenario, you’ve taken your trainers on holiday with you. The temperature is above 32 degrees and the humidity is high. On this run, the still, moist air keeps your sweat from evaporating. Your running clothes and skin get saturated, and sweat starts dripping off you. Because the sweat you’re pumping out isn’t really cooling you, your internal heat load remains high, and you keep sweating a lot. Pretty soon, you’re working much harder to maintain the same pace or, more likely, you’re slowing. This is when lowering your sweat rate with cold beverages should produce a net cooling effect, Jay and Morris write.

Unfortunately, there’s not a ballpark wet globe bulb temperature (WGBT) above which cold drinks should be overall beneficial. (WGBT attempts to capture the combination of heat and humidity.) “This is okay for indoor environments, but not outdoor environments that contain significant radiant heat sources (e.g. the sun) and ambient air flow,” Jay wrote in an email. A chart in Jay’s and Morris’s article shows a wide range of temperature and humidity during which cold drinks should help runners, starting with a temperature of just under 20 degrees celcius and 80 percent humidity, to roughly 26 degrees and 40 percent humidity, on up to 32 degrees and 30 percent or less humidity.

In general, if the combination of your pace and the heat and humidity leads to sweat dripping off your skin, colder drinks should help keep you cooler. Although research on the topic has used cold water, Jay said that cold sport drinks should produce the same effect.

This article originally appeared on Runnersworld.com