Pre-drinking to hyperhydrate, and other heat-related research


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There’s a great (and timely) article called “Myths About Running in Heat” in the current issue of Running Times (linked to from Amby Burfoot’s latest blog entry), in which Phil Latter takes a look at six common myths relating to topics like thirst and acclimatization. It’s all good stuff, and worth a read.

The one that I hadn’t really thought about before was the idea of “hyperhydration” before running in the heat. In general, if you try to load up on fluid in the days or hours before a run, you’ll just pee it out. But Latter suggests two options. First:

Hyperhydrating, or drinking more fluid than is necessary to maintain fluid balance within the body, is effective right before an event because blood flow is severely reduced to the kidneys during exercise, thus limiting fluid excretion. “The trick then is to be able to absorb quickly and then tolerate the bloating feeling for a couple of minutes into the exercise period,” says [University of Sherbrooke exercise physiologist Eric] Goulet. “As the exercise progresses the intestine will slowly absorb the fluid, which will then be used for physiological regulation.”

Second is the idea of drinking “lightly salted water in the several hours preceding hot weather exercise” — a technique with a long anecdotal history that Goulet is currently testing in the lab:

The biggest trick, Goulet concedes, is making the substance palatable. For his trials, Goulet had the salt water ( just over ¼ teaspoon of table salt per cup) blended with Crystal Light and served at roughly 35 degrees, but adds, “You have to find what works best for you.”

One other interesting point is the idea that drinking fluids helps you deal with heat better — a claim that most people (including exercise physiologists) accept absolutely uncritically. Not everyone agrees, though:

After performing a thorough meta-analysis, Loyola University’s Jonathan Dugas, a well-known blogger on the Science of Sport website, explains why. “I’m not saying there’s no effect of fluid on body temperature, but you have to really qualify it,” he says. “The effect is really small. Maybe a half degree in temperature, maybe less.” […]

His research suggests hydration levels have almost no effect on one’s likelihood of suffering from even the most extreme of all heat-related issues, heat stroke. […]

“On a very hot day,” Dugas says, “no amount of drinking is going to change the fact that you’re going to go slower. You can drink up to 100 percent of your body mass, and it won’t keep you from running slower.

For practical purposes, of course, this doesn’t mean that water isn’t a special concern on hot days. The heat will make you sweat more, so you’ll need to drink more that match thirst. But it challenges the widespread assumption that when someone at a race collapses from heat stroke, one of the causes was that they didn’t drink enough water:

Current research suggests that some combination of genetic predisposition, infection, muscle damage, sleep deprivation and high levels of exertion may lead to heat stroke… water intake (or the lack thereof) isn’t mentioned.


6 Replies to “Pre-drinking to hyperhydrate, and other heat-related research”

  1. Has anyone done research into day-before drinking of iskiate (hydrated chia seeds, often mixed with sugar and lemon juice) in terms of effect on next-day hydration? Since the chia seeds absorb water and form a gel-like substance, my anecdotal feeling is that their water is released more slowly and thus can help over a longer period of time.

    As far as making salted water palatable, salt/potassium tablets would seem to be the easy solution, rather than drinking something that’s utterly vile.

    I totally cannot imagine hyperhydrating right before exercise; drinking more than a small amount right before or during exercise is a sure-fire way to a side-sttich for me as a runner.

  2. I recall reading about a study comparing different pre-exercise drinks (plain water, carbohydrate drink, carbohydrate-protein drink, and broth). Broth turned out to be one of the better choices. Because of the salt?

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