4 Things That Happen to Your Body During Zone 2 Cardio

A new fitness trend is gaining traction among athletes and casual exercisers alike for hitting a sweet spot in intensity—not too easy, not too tough. It’s called zone 2 cardio.

With zone 2 cardio, you’re working at about 60% to 70% of your estimated maximum heart rate during cardiovascular activity, Kimberly Burbank, MD, a sports medicine fellow at UCLA Health, told Health. Think moderate-intensity movement like brisk walking, light jogging, cycling, moderate rowing, or hiking.

Curious about zone 2 training? Here’s what it may do for your body.

Training in zone 2–the second of five heart rate zones—is a great way to burn fat while saving energy for more strenuous activity later. 

At this lower-intensity level, your body mainly relies on fat to fuel your movement, Burbank explained. Over time, it may start producing more mitochondria—the structures in cells that generate energy—so you get more efficient at burning fat.

The bonus? You could have more carbohydrates in reserve when you need them for higher-intensity workouts.

Like other forms of exercise, consistently training in zone 2 can help protect against a range of chronic health issues over time. 

One key benefit is a reduced risk of type 2 diabetes, Burbank said. Zone 2 cardio activates something called skeletal muscle glucose uptake—aka when your muscles pull sugar from the bloodstream to use for energy. With regular training, your body gets better at this process, meaning your muscles need less insulin to absorb glucose, which can improve insulin sensitivity.

Zone 2 training also gives your heart a boost, added Christopher Travers, MS, an exercise physiologist at the Cleveland Clinic. It increases blood flow and helps your body produce more red blood cells, key for delivering oxygen to your muscles and organs.

Zone 2 workouts are among the most effective for building endurance, Travers noted. That’s largely because this type of training boosts both the number and efficiency of mitochondria, “improving your body’s ability to sustain longer workouts,” he explained.

However, Burbank cautioned that relying solely on zone 2 cardio can backfire—potentially limiting your ability to perform higher-intensity activities like sprinting and heavy lifting. Over time, this may reduce speed and lower VO2 max, a measure of how much oxygen your body can use during intense exercise.

The less intense zone 2 workouts put less strain on your muscles and joints, which can reduce the risk of injury compared to higher-intensity exercises, research suggests.

But Burbank noted there may be a temptation to do these lighter workouts for longer or more frequently. Over time, that can actually increase your risk of developing overuse injuries, such as shin splints, tendinopathies, and patellofemoral pain syndrome, she warned.

Incorporating zone 2 cardio into your routine is a good choice if you’re looking to improve endurance, fat metabolism, or overall cardiovascular health, Travers said.

When doing zone 2 cardio, it’s best to sustain steady, rhythmic, full-body movements for an extended period, he explained. One way to gauge if you’ve hit zone 2 is by your perceived level of exertion—around a three or four out of 10, Burbank said. For example, during a brisk walk, you should still be able to speak in full sentences.

Burbank added that a typical zone 2 session lasts about 30 minutes, but can extend to 120 minutes depending on your training goals. 

She generally recommends doing zone 2 workouts two to three days a week, combined with other forms of exercise, such as strength training or high-intensity training. This approach helps “maintain muscle health, bone health, and anaerobic capacity,” Burbank noted.

Zone 2 cardio refers to moderate-intensity workouts like brisk walking or cycling that raise your heart rate to about 60% to 70% of your maximum. These workouts benefit the body in several ways, from improving endurance to helping protect against chronic health conditions. While zone 2 workouts are valuable, experts recommend doing them alongside higher-intensity exercise for a more balanced fitness routine.