Staying Hydrated On Long Runs

A new study finds that “intuitive” drinking during a long running race improves performance compared to drinking by the rules.

This article was originally published in the Jan./Feb. 2013 issue of Inside Triathlon magazine.

If you’ve been a triathlete longer than a week, you’ve probably been advised at least once—perhaps dozens of times—to consume enough sports drink during races to completely offset weight loss from sweating and to provide 60 grams of carbohydrate per hour. The rationale behind these recommendations is that full rehydration elevates performance by aiding temperature regulation and reducing cardiac strain, while absorbing carbs at the highest rate possible helps keep muscles topped off with precious glycogen.

Lately, however, these longstanding guidelines have been challenged by studies indicating that, during running at least, such high rates of fueling can cause gastrointestinal discomfort and offer no performance benefit compared to just drinking by thirst. A new study (conducted by Dr. Ian Rollo and colleagues at England’s Loughborough University and published in the International Journal of Sport Nutrition and Exercise Metabolism) provides strong support for an at-will drinking strategy during short-duration endurance exercise.

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Nine experienced recreational runners participated in the experiment (see the chart on page 2). Each of them completed a 10-mile road race on three separate occasions, drinking nothing during one race, drinking a carbohydrate-electrolyte sports drink by thirst during another race (which came to an average of 10.6 ounces per hour), and drinking at a prescribed rate aimed to provide the recommended 60 grams of carbs per hour in the remaining race (which came to 35.7 ounces per hour).

In addition to timing the three races, Rollo’s team took measurements of dehydration, core body temperature and gastrointestinal distress. Performance in the no-drinking and prescribed-drinking trials was almost identical. But the runners covered the 10-mile course almost a minute faster on average when allowed to drink according to their thirst.

Rollo says that further research is needed to determine why the runners performed better with intuitive drinking despite becoming significantly more dehydrated and taking in 70 percent less carbohydrate compared to the prescribed-drinking trial. One possible explanation is suggested by the runners’ subjective ratings of gastrointestinal discomfort, which were significantly higher throughout the second half of the 10-mile race in which they were prescribed a heavy dose of sports drink.

It’s important to bear in mind that this study involved a race of relatively short duration and subjects who were mostly unaccustomed to drinking during exercise. The one subject who did routinely use a sports drink in training—who happened to be a triathlete—was also the only subject to record his best time in the prescribed-drinking trial. Thus, the authors of this particular study recommend that athletes practice ingesting carbs and fluid in training sessions lasting longer than one hour to optimize performance come race day.

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Click “next page” for a look at the experiment.