Zone in

The fitness-sphere won't stop talking about how low-intensity cardio-sometimes called zone 2 training-is so good for you. But does all this easy work really do anything?

- By Marty Munson

A minute ago, high-intensity interval training (HIIT) was king. Now that gut-it-out-and-get-the-glory work might need to share the crown with slow and steady efforts, thanks to what they do for your body, your longevity and maybe even your mind. These are the famous zone 2 workouts-keeping your heart rate between about 70 and 80 percent of its maximum-that runners, smart gymgoers and everyone with a podcast is talking about these days. Think of zone 2 as the range between easy and moderate cardio, where you can carry on a conversation but someone on the other end of a phone would know you're not sitting down. (See "Get in the Zone" on the next page.)

What happens in zone 2 powers up your endurance, your lifting routine and your general performance as a human being, proponents say. Here's what to know about the zone.

LITTLE EFFORT, BIG GAINS

Endurance athletes, such as marathoners, cyclists and Ironmen, have long understood that zone 2 training is a key to performing well on race day. Look at Eliud Kipchoge, the world's fastest marathoner, who spends four days a week running in zones so low that any decent runner could keep up with him. Lower-zone training yields high results in endurance sports, says Dr. Mike T. Nelson, a certified strength and conditioning specialist, possibly "because the athletes aren't out there just trying to fry themselves crazy every single day." Along Z2 effort today leaves room for more time on your feet or in the saddle the next day. But another huge perk of Z2 training, no matter your sport, is the adaptations your body is making deep within your cells.