The Pros and Cons of Running Twice a Day

Heading out for two runs in a single day—logging "doubles" or "two-a-days"—is standard practice among elites. But most mortals wouldn't dream of it: not enough time and too much injury risk.

"There is a misconception that doubles are something only high-mileage, elite runners do," says Steve Magness, an exercise physiologist and cross-country coach for the University of Houston. "But a lot of runners can benefit from them." Including time-crunched folks trying to squeeze in miles and veterans looking to step things up. For good reason: Studies suggest doubling up and running in a depleted state can boost fat-burning, train the body to use glycogen more efficiently, and stimulate mitochondria production (more mitochondria can delay fatigue).

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"By shortening the time between runs, you're challenging your body to recover faster," says Greg McMillan, an exercise physiologist and coach in Flagstaff, Arizona. "And a faster recovery is a good thing." But bad things can happen if you overdo it. Here's when it makes sense to double up—and how to do it safely.

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"Cumulative mileage matters—no matter how you do it," says Brad Hudson of Hudson Elite Marathon Performance in Boulder, Colorado. You can boost your total miles by doubling once a week—and still keep a rest day.

4 to 10 hours after a key workout like an interval session or a tempo run, go for an easy 20-to 45-minute run, and don't fret about pace. This will boost mileage and aid recovery from the first workout by increasing blood flow to the muscles and flushing out lactic acid and other metabolic waste products. The result? Fresher legs for your next run.

"The best massage you can get is from a second run," says Hudson. On days you can't bear the thought of lacing up again, try pool-running, cycling, or the elliptical (try these four workouts borrowed from other sports to mix it up.) Such options offer similar recovery benefits without the pounding, says Hudson.

More: Distance Running: How Many Miles Should you Run?

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