Why you can run 10 miles but get winded walking up stairs

We're all predestined to be a certain type of exerciser. But it's not set in stone.

Ever met a distance runner who couldn't walk up three flights of stairs without panting? Or a group fitness devotee who loses steam after a mile on the treadmill? Among even the most avid exercisers, all cardio is not created equal. And it turns out science has something to do with it.

Deciphering Your Cardio DNA:“We are all genetically predisposed to being good at certain types of activities, depending on our muscle fiber makeup,” says Alex Zimmerman, an exercise physiologist and manager of Equinox’s Tier 4 program. “People with more slow-twitch fibers (Type A) tend to have better endurance, while people with more fast-twitch fibers (Type B) are better at producing short, explosive movements, such as jumping or sprinting.” And both types process oxygen differently during exercise, which is why you might feel like you’re going to die on the stairs but power through on marathon day.

How to Change It:“If you learn to train efficiently, you can shift your actual muscle fiber makeup,” he says. For example, you may be genetically predisposed to be an endurance athlete, but if you focus on doing hill repeats or intervals, instead of always logging slow, steady miles, you could grow your ability to perform anaerobically (at a high intensity, for a short period of time). Or vice versa.

One of the best ways to determine how exactly you should be training is to take a V02 max/cardio efficiency test, now available at E at Columbus Circle. For 15 minutes, you'll be put through a series of moderate to high-intensity exercise, while wearing an oxygen mask and hooked up to a metabolic cart. “With this new technology, we’re able to detect the precise moment in time when your energy system shifts from being aerobic to anaerobic, and when you reach your anaerobic threshold (the point at which lactic acid builds up in your body faster than it can be cleared away). We then create a customized cardio program that promises positive training adaptations,” says Zimmerman.

Just be sure to create a balance between easy, medium and hard routines each week. "You should always work at a speed or level that you can only maintain for the duration of that particular workout,” he notes. If you’re going to be out for an hour or more, go easy. Only have 10 minutes? Ramp it up. “Mixing it up will ensure that you’re maximizing all of your energy systems and activating all your muscle fibers.”