How bad hydration habits can hurt your race time

Misunderstanding the role of hydration, heart-rate, and sweat-rate is a mistake many runners and marathoners make. Here's how to avoid it.


A runner’s need to hydrate is pretty intuitive; prolonged cardio just makes you thirsty.

But misunderstanding the role of hydration, heart-rate, and sweat-rate is a mistake first-time marathoners (and other runners) often make, says Ross Markowitz, who oversees training for the renowned marathon training program at La Palestra, a high-end wellness center that bridges the gap between fitness and medicine.

And increasing your understanding can get you across the finish line faster: “The ability to balance and control the system’s demand for oxygen via hydration may be the single most important factor for performance in endurance sports,” he says. (Are you as shocked as we are?)

Excellent hydration know-how is especially important in New York, where locals do the bulk of their training for the ING New York City Marathon during summer months, when the heat can be crippling. (You haven’t forgotten about last week already, have you?)

We asked Markowitz to help us understand how your hydration habits influence your body’s ability to propel you through a long run, so that you’ll never be tempted to skip a water station again.

Ross Markowitz
La Palestra’s Ross Markowitz

This is your body on a run

When you run, your heart pumps harder, so that it can deliver the extra oxygen you need to your cells. With your blood pumping super fast, your core temperature heats up, and the body moves the heat out of your body, to cool you down, in the form of sweat. Losing water as you sweat also reduces your blood volume, since 90 percent of your blood volume is water. This makes it harder for the heart to keep pumping enough oxygen-rich blood around.

“The need to stay hydrated is the need to replace what you’re losing so the heart doesn’t have to work harder to deliver oxygen,” Markowitz explains. In other words, you won’t just feel parched, your body won’t be able to support your time goals.

How to hydrate like a pro

Markowitz has a few recommendations. And none involve drinking gallons of water before a run—you can only absorb a certain amount and it’s uncomfortable to run with a sloshing belly.

You should, however, start off hydrated and stop for small sips, not gulps, along the way. As you go, pay attention to your “Rate of Perceived Exertion.” If you normally feel great at mile five and today you’re hurting like crazy, you didn’t drink enough. “That perception that I’m working harder, that’s an indication that I need to get on the hydration,” he says.

In La Palestra’s marathon program, they also weigh themselves before and after a run to see how much weight was lost in sweat. “You don’t want to lose more than two percent of your body weight, no matter how long the run,” Markowitz cautions. If you do, plan on upping your water intake before your next run.

Why wearing clothes that wick really matters

Apparel also matters, and Markowitz’s rule is ABC, for “anything but cotton.” “If you have a soaking wet shirt, the sweat can’t evaporate,” he says, which means your body will have a hard time secreting new sweat, making it hard to cool down. Go for something with a high-performance, sweat-wicking fabric instead. You’ll look less like you went for a swim after, too. —Lisa Elaine Held

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