Zone 2 Cardio: Myths, Misconceptions, and Four Steps for Implementation
Over the last five years, we’ve been inundated with the benefits of Zone 2 cardio. Popularized by podcasters, authors, and social media influencers (many with advanced degrees who are simply far outside of their scope of expertise), Zone 2 cardio can be defined as low-intensity cardio (longer, slower walks; “easy” bike rides or runs; and a focus on keeping one’s heart rate relatively low).
Zone 2 cardio has been touted as the key to improving mitochondrial efficiency and delivering robust, health-protective, and performance benefits. We’ve even been told that if we accidentally exercise harder and, thus, move out of Zone 2, we are at risk of compromising these benefits.
A team of Canadian researchers recently published a review in the scientific journal Sports Medicine that might be the most important exercise science publication in 2025 (in my opinion), titled:
Much Ado About Zone 2: A Narrative Review Assessing the Efficacy of Zone 2 Training for Improving Mitochondrial Capacity and Cardiorespiratory Fitness in the General Population.
I’m not going to recap the entire paper (I recently had a discussion with Dr. Brendon Gurd, the lead author on this paper, on the Discover Strength Podcast—listen here if you’d like a deeper dive). Instead, I’m going to summarize how we can implement the research findings into our cardio routine.
A simple and scientific approach to cardio:
High-intensity cardio, whether interval training or steady-state training, is more effective for improving mitochondrial efficiency and health outcomes than Zone 2 training. The podcasters/pundits were wrong about Zone 2.
1–3 times per week, focus on working harder (think: heart rate elevated, breathing hard, and unable to carry on a conversation) for 12–30 minutes on a run, fast walk, elliptical, rower, stepmill, or whatever form of cardio you enjoy/tolerate. This is the foundation of your cardio. A simple but effective interval approach would be to work hard for 1 minute and then recover for 2 minutes (repeated for a total of 8 reps).
10,000 steps probably shouldn’t be your goal. Instead, a little bit of hard/intense cardio should be the focus. And then, if you enjoy a walk with your partner, a stroll while listening to a podcast (my favorite), or walking as transportation (another favorite of mine), include this—but include it in addition to the more intense cardio, not in place of it.
Caveat: The research is unequivocal: doing something (slow walking) is better than doing nothing. If you have a choice between nothing and walking or focusing on steps, by all means, focus on walking and increasing steps. But if you have a choice between Zone 2/walking and more intense cardio, choose more intense cardio.Cardio isn’t effective for weight loss. Cardio is incredibly effective in delivering health-protective benefits (far more effective than most people appreciate). Cardio is far less effective for weight loss than most people assume. I repeat: don’t do cardio to lose weight. We named it “cardio” for a reason.
Bonus: If you are a marathon runner or endurance athlete, research shows that high-intensity cardio is the foundation of adaptations that will boost your performance. Focus on a few key runs/workouts per week (speed, tempo, long run with pace work), and then layer in more “easy” Zone 2 running. Don’t aim for an 80/20 polarized approach; instead, focus first on the quality, higher-intensity miles and then layer in as many easy miles as you prefer. For example, a marathon runner might run 55 miles in a week, with about 20 of these miles performed at a high level of intensity and the remaining 35 performed at an “easy” pace. This would be a 36/64 approach (a totally appropriate ratio for a marathon runner running 55 miles per week). Yes, elite marathoners who run over 100 miles per week gravitate toward an 80/20 polarization, and there is likely something to this, but science has yet to uncover the physiological mechanism at play (and, to be clear, this is driving performance, not health-protective benefit).
