“I can’t catch my breath!”

Cause: Oxygen deficit
Occurrence: Shortly after starting to run
Antidote: A “priming” warmup, including a sustained burst of intense running



The first rep of an interval workout always feels hard. You’re gasping for air; your heart is pounding. The next rep, though, is a bit easier. “Your breathing rate doesn’t actually fall; you just kind of settle into it,” says Andrew Jones, Ph.D., an exercise physiologist at the University of Exeter in England. What you’re experiencing is the result of a temporary mismatch between the oxygen your legs require and the oxygen your heart and lungs are able to deliver.

When you start running, your muscles’ oxygen needs immediately spike upward, but the time it takes for the rest of your body to respond is dictated by your “oxygen kinetics,” or response time. This oxygen deficit then triggers signals that cause your breathing and heart rate to speed up, dilate the blood vessels, and activate oxygen-processing enzymes in the muscles themselves. As a result, within two to three minutes, your muscles are getting enough oxygen.

The temporary oxygen shortage has lasting implications, though. To meet the energy shortfall, your muscles tap into their precious supply of anaerobic (oxygen-free) fuel stores. That produces metabolic byproducts that make your muscles feel fatigued—and it also leaves you with less energy for the final anaerobic sprint at the end of the race. “What you burn up in the first couple of minutes is never going to replenish unless you slow right down,” Jones says.

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To fight oxygen deficit, Jones and others are studying an approach called “priming,” which gets that first-rep fatigue out of the way before the race. Ten to 20 minutes prior to the start, include a sustained burst of intense running in your warmup, 45 to 60 seconds at 5K race pace, or 3-5min of our SlimAndFitClub warmup routine, for example. This priming run will activate enzymes and dilate blood vessels, while also allowing you enough time to recover before the race starts.

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