Zone 2 Cardio Is Trending. But Is It Really Better for You?

“Run slow to run fast” goes the Zone 2 rallying cry that has taken the fitness internet by storm. Over the last three years, this once-obscure sports-science concept has become gospel for many recreational athletes. Running influencers and health podcasters frequently talk about the benefits of low-intensity exercise. Many runners are slowing down their “easy” runs. And TikTokers are promoting incline walking (like the 12-3-30 workout) as the key to fat loss, longevity, and hormonal balance. Keeping your heart rate low—about 60% to 70% of your max—seems to have become a near-universal goal for the health-conscious.

Zone 2, in case you somehow missed the wave, refers to low-intensity cardio where you keep your heart rate just below your aerobic threshold (the point where your body shifts from primarily burning fat to using carbohydrates for fuel.) While doing it, it’s easy enough to hold a conversation, but hard enough to feel like you’re exercising. And, as an exercise category, it has been praised for building mitochondria, improving fat metabolism, and keeping cortisol levels in check (more on all of that later.)

But the backlash has officially arrived. A 2025 literature review published in Sports Medicine has stirred up debate about whether steady-state, low-intensity cardio is actually the most effective form of exercise—especially for time-crunched, non-endurance athletes. Social media has responded, of course, with videos like “Stop doing zone 2” and “Zone 2 training will only get you worse.”

As with most online fitness trends, the truth is more nuanced. Here’s what you actually need to know.

The rise of zone 2

Throughout the 2010s, at the start of the boutique fitness boom, companies and trainers marketed brutal workouts as the only type of workouts that mattered. People stacked CrossFit WODs and OrangeTheory classes five days a week, pushing their body to the point of vomiting or passing out every time they worked out (often cheered on by bootcamp-sargent coaches who lean in to the whole “push until your drop” mentality.) Unsurprisingly, that approach wasn’t sustainable for most people, especially beginners. (Between 2000 and 2019, ER visits related to rhabdomyolysis—a dangerous form of muscle breakdown—rose more than tenfold. Though we have no proof that that was due to high-intensity workout classes, it’s a notable statistic.) And yet, the collective belief that a “good workout” means feeling completely annihilated became so ingrained in American society that many of us still have a hard time taking it easy at the gym.

So when zone 2 cardio gained traction around 2021 after recently disgraced longevity bro Peter Attia did a deep dive on the topic, it felt like a much needed relief. He wasn’t the first health influencer to advocate for it. Exercise physiologists, like Stephen Seiler, had been researching low-intensity endurance work for decades. It first got popular in the cycling world around 2010, then trickled down to marathon runners, then the masses.

“For two and half decades, we’ve been trying to tell people, ‘Hey, don’t go hard every day. You cannot do it. Elite athletes don’t do it,’” Seiler says. He’s best known for advocating for “polarized training,” which promotes a split of roughly 80% low-intensity (zone 2 or lower) and 20% high-intensity work. For elite athletes logging tens of hours a week, this split is especially helpful for recovery while still remaining active each day.

But once the concept hit the wellness world, people started treating zone 2 like a miracle drug: What was once a necessary training tool for elite athletes’ exercising became commonplace for everybody, no matter their training load. Influencers cited it as key to longevity, because it could build mitochondrial density (which is important because mitochondria produce energy) and improve metabolic efficiency better than other forms of exercise. Health and wellness podcaster Andrew Huberman even claimed that everyone should get at least 150 minutes a week of zone 2 because it could improve every other aspect of training, like resistance training and speedwork.