Much Ado About Zone 2

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! Have a listener question, a comment or an idea for an episode? Email us at [realexercisescience@gmail.com](mailto:realexercisescience@gmail.com) **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: This is What Zone 2 Training Looks Like Attia saying 80% of cardio should be Zone 2 Origins of Zone 2: Attia and San Milan in the early days of the trend Find Stu Phillips on most platforms @mackinprof Find Martin Gibala on Instagram, which he just joined, @gibalamj Exercise Science is powered by EverMe. Download EverMe for free at your favourite App store. **DISCUSSION POINTS** 00:00 Exercise fads 00:34 Intros 02:30 What Zone 2 is 04:21 No uniform definition 06:02 Lactate threshold 08:10 Zone 2 marker variability 09:54 Ventilatory threshold 11:57 Conflation with moderate 12:58 Improving exercise prescriptions 14:40 Health v. performance 16:04 Moderate intensity is better 16:58 80/20 split 18:45 Better alternatives 19:47 Zone 2 origins 20:39 Wearable intensities 22:09 Threshold testing options 23:14 Training for health 24:21 Take-home message 26:05 Vigorous is better 26:44 Listener question **DISCLAIMER** The Exercise Science podcast is for educational and entertainment purposes only and is not a substitute for professional medical advice. Strength training and fitness carry inherent risks. Always consult with a physician or qualified healthcare provider before starting any new exercise program or making changes to your diet. The hosts, producers, sponsors and guests of this podcast disclaim any liability for any injuries or losses connected with the information discussed in this show. The science of strength and fitness is continually evolving. While we strive to provide accurate, evidence-based information, we make no representations or warranties regarding the completeness, accuracy, or timeliness of the information discussed. This is a public episode. If you would like to discuss this with other subscribers or get access to bonus episodes, visit www.realexercisescience.com