Why you need Zone 2 training in your training plan

A minute ago, high-intensity interval training (HIIT) was king. Now that gut-to-glory job may need to share the crown in slow and steady effort, thanks to what they do for your body, your longevity, and maybe even your mind.

These are the popular Zone 2 workouts that keep your heart rate at about 70 to 80 percent of its maximum that runners, smart gym-goers, and anyone with a podcast are 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 the phone would know you’re not sitting. (Learn more about how to know you’re in the zone by checking the table below.)

What happens in zone 2 boosts your endurance, your lifting routine, and your overall performance as a human being, advocates say. Here’s what to know about the area.

How easy effort brings you gains

Endurance athletes, such as marathon runners, cyclists and Ironmen, have long understood that training in zone 2 is the key to performing well on race day. Look at Eliud Kipchoge, the world’s fastest marathon runner, who spends four days a week running in areas so low that any decent runner could keep up with him. Lower zone training yields high results in endurance sports, says Mike T. Nelson, Ph.D., CSCS, owner of Extreme Human Performance, perhaps because athletes aren’t out there just trying to go crazy every single day. A long Z2 effort today makes way for more time on your feet or in the saddle the next day. But another huge benefit of Z2 training, no matter your sport, is the adaptations your body is making deep within your cells.

It all goes back to your mitochondria, the parts of your cells that generate ATP, which is the fuel that drives muscle contractions. As you age, your mitochondria become a bit like an old dog’s coat: sparse, damaged, and inefficient. Zone 2 cardio basically helps build your mitochondria, says Kenneth Jay, Ph.D., a sports scientist who has done research with the National Research Center for the Work Environment in Copenhagen. These workouts help you produce more of those cellular powerhouses and shed the old, damaged ones. When you get out of that zone, you start using a different energy system that doesn’t stimulate the mitochondria to the same extent.

These cellular enhancements can help you gain weight in the lift as well, aiding recovery between sets. People without abundant healthy mitochondria simply don’t have the ability to regenerate ATP fast enough to repeat something. And what they’re repeating is half the result of what they were doing in the beginning, so they’re not getting as much stimulation as they could, Nelson says.

Building mitochondria may not get you ripped out, but it deserves a lot of credit given that mitochondrial dysfunction has been linked to cardiovascular disease, cancer, diabetes and obesity. Backing them up with the Z2 essentially gives you a more efficient engine to tackle life. It’s like a hybrid car, explains Stephen Seiler, Ph.D., a professor of sports science at the University of Agder in Kristiansand, Norway, who has studied the effects of high- and low-intensity zone training in athletes . Scaling your workouts reduces battery power. You can run the battery down for a while, but to pay it off you need to have your own main engine. Z2 constant work not only helps you recover better between sets or workouts, it also helps you improve at everyday challenges: a family hike, an extra-long run to your flight gate, or a grueling workweek .

Does zone 2 work for strength cardio?

In general, yes. That’s because a big benefit of zone 2 cardio is that it helps keep your heart strong and, ultimately, supple. When you lift heavily, the left ventricle of the heart, the one that pumps oxygenated blood to the rest of the body, also becomes stiff. Heavy loads cause your heart to contract in a way that makes it lay down more muscle fibers. But it lays them inside the chamber, so there’s less room for the blood. (Don’t get complacent, endurance folks; too much cardio makes yours too thin and can leave you vulnerable to problems like atrial fibrillation.) Zone 2 cardio moves blood through the heart in a way that keeps the walls at a healthy thickness and stretch, so it works better, says Jay.

Exactly how much time you need in Z2 to get the benefits is discussed. If you’re mostly sedentary now, any amount of low-intensity movement will help. If you’re fairly or very fit, experts typically advocate a minimum of 30 to 40 minutes of zone 2 cardio twice a week. (For endurance athletes, 80 percent of total training volume in Z2 is a good guideline). The trick is not to turn that cardio workout into an endorphin rush. Once you start pushing the intensity, cellular byproducts (lactate) start to build up and a different energy production process starts to take over. And that’s not what you want to train in these workouts.

Zone 2 is a chat-paced job, so bring your friends. Fit people may need more than a casual stroll; uphill hiking and rucking can get you there. Keep it interesting at the gym by dedicating ten minutes each to the rowing machine, bike, and treadmill. The key is control. There’s also a warrior aspect to this, Seiler says. When you have the discipline to stay in the zone, there can be a Zen about going out and finding your own pace and not being swayed by the person running past you that day, she says.

When it comes to creating a more efficient engine, easy really does it. It’s not that you can’t do hard workouts or go home; you need those too. But being smart about adding some bass can fuel your high.

Marty Munson, currently the medical director of Men’s Health, has been the health editor at properties including Marie Claire, Prevention, Shape and RealAge. She is also certified as a swim and triathlon coach.