What Is Proper Hydration and How It Affects Running Performance

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Proper hydration is a constant struggle for runners, especially in the hot summer months. While much has been said and written about the topic, a new study out of the University of North Alabama presented at the American College of Sports Medicine's annual meeting further emphasizes the importance of monitoring hydration levels.

Researchers rounded up 13 distance runners and had them run a 75-minute evening run, followed by a 10K time trial the next morning on two separate occasions. They monitored sweat loss, hydration and 10K performance in both instances. The difference between these two evening/morning runs was how much the runners drank. After one of the evening runs, they rehydrated 75 percent of their sweat loss, which is typical of what many runners do. After the other evening run, they rehydrated 150 percent of their sweat loss, which is what the American College of Sports Medicine suggests.

The difference in 10K performance the following morning during both experiments was striking. When runners replenished 150 percent of their sweat loss, their 10K times were on average over a minute faster, which was a three percent improvement over running at the 75 percent hydration state. Put into other terms, that could be the difference between a 4:00 and 3:52 marathon.

More: Hydration Tips for Better Athletic Performance

The researchers concluded that while 150 percent replacement of sweat loss may be overkill, runners should be replenishing at a rate of slightly over 100 percent to garner performance benefits.

This, of course, isn't surprising news to most coaches. "The importance of hydration cannot be overstated, and for most busy runners, it can be hard to remember that water bottle," says Rebecca Scritchfield, a Washington D.C.-based nutritionist and ultramarathoner.

More: Hydration: What to Drink, When and How Much

How Much to Drink

The complicated part is knowing when and how much to take in. The answer, unsurprisingly, isn't as straightforward as many runners would prefer. "There is so much advice out there about how much to drink; people are often confused," says Scott Fishman, the brains behind the Running Scientist blog and founder of Team All-American in New York City.

Not only does the recommended fluid intake vary from one individual to another, but temperature and climate also play a role. To be sure, having a hydration strategy that works for you, before, during and after your runs, can make all the difference when it comes to the numbers on the clock.

While the American College of Sports Medicine recommends taking in 16 to 24 ounces of fluid for each pound lost during exercise, it can be tricky to know what exactly that number should be for you. "Fluid needs vary widely from person to person, so it is challenging to make general recommendations," explains Scritchfield.

She suggests weighing yourself before and after a run to figure out your sweat rate. "If you find that you lost four pounds while running, you know that those four pounds are due to fluid losses," she explains. Doing the math, 4 pounds x 16 ounces = 64 ounces and 4 pounds x 24 ounces = 96 ounces. This means you should consume somewhere between 64 to 96 ounces, or at least four 20-ounce bottles of fluid that day.

More: How Calculating Sweat Loss Can Boost Your Performance

Fishman also recommends hopping on the scale pre- and post-run, saying that what you eat can also contribute to replenishing your fluid losses. "Foods like cantaloupe, strawberries and watermelon are all foods you could eat that would help you rehydrate," he says.

More: 8 Hydrating Foods to Eat When Training in Hot Weather