Episode Details

Influencers can’t get enough of Zone 2 training. So why did Martin Gibala publish a research paper challenging Zone 2 for the general public? In this episode, Stuart Phillips leads Marty through a critical examination of Zone 2.

Marty suggests that very little scientific research exists to support Zone 2 training intensity for most people—either as an effective stimulus for cardiorespiratory fitness or mitochondrial capacity. In fact, if you do between three and six hours of cardio a week, Marty believes that Zone 2 isn’t hard enough for you to efficiently accrue training benefits. In other words, if you’re an amateur athlete subscribing to the much-vaunted rule that 80% of your cardio should be in Zone 2, you’re not as fit as you otherwise could be.

So what is Zone 2 training? And is Zone 2 causing many people to exercise inefficiently, leaving them less healthy than they otherwise might be? What should people be doing INSTEAD of Zone 2? It’s all here, in the latest episode of Exercise Science!

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LINKS

Marty and Brendon Gurd’s critical examination of Zone 2: 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

Marty’s coauthor Brendon Gurd on their Zone 2 paper at the Discover Strength podcast.

Luke Carlson calls the “Much Ado About Zone 2” paper the most important scientific publication of 2025 in this blog post summarizing the paper.

HIIT and Zone 2: Marty on the Discover Strength podcast

Sperlich paper referenced in this episode: Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries

Marty was a coauthor on this ACSM/ESSA position statement on exercise intensities

Marty was senior author on this Sports Medicine paper on exercise intensity in high-intensity activity, which features the intensity diagram Marty mentions

Referenced in this episode: Defining Training and Performance Caliber: A Participant Classification Framework

Lifehacker’s Beth Skwarecki notes, Nobody Can Agree On What Zone 2 Is

Oura’s heart rate zones

Whoop band’s heart rate zones

Garmin’s heart rate zones

Peter Attia on Zone 2: This Is How You Know If You’re in Zone 2 When Doing Cardio

More Attia:

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