Podcast Summary: Sigma Nutrition Radio, Episode #571

Title: Is Zone 2 Training Actually Best for Health?
Guest: Prof. Brendon Gurd
Host: Danny Lennon
Date: July 29, 2025

Episode Overview

In this episode, Danny Lennon sits down with Professor Brendon Gurd, a leading researcher in exercise physiology at Queen’s University, to critically examine the popular claims surrounding Zone 2 training and its purported health and performance benefits. Drawing from a recent comprehensive review ("Much Ado About Zone 2"), they unravel the scientific evidence (or lack thereof) backing Zone 2’s superiority for improving mitochondrial capacity, cardiorespiratory fitness, and overall health, especially in the general population.

Key Discussion Points and Insights

1. What is Zone 2 Training? [06:24-07:57]

• Physiological Intensity Domains:
  Prof. Gurd explains exercise intensity using three physiological domains:
  • Moderate (below first lactate threshold; low glycogen use; relies on fat; low lactate)
  • Heavy (above lactate threshold but below critical power; more glycogen use; more fatigue)
  • Severe (above critical power; reaches VO2 max quickly; high fatigue)
• Zone Models:
  In a common 5-zone model, Zone 2 sits at the upper half of the moderate domain, just below the lactate threshold.
  • "Zone two typically is in a 5 zone model of intensities... below lactate threshold in that pretty easy intensity domain where we’re again relying on fat, not utilizing a lot of carbohydrates." – Prof. Gurd [07:48]

2. Zone 2’s Popularity and Elite Athlete Practices [08:15-09:11]

• The origin of the Zone 2 hype seems tied to elite endurance athletes’ “polarized training”—about 80% at low/moderate (Zone 2) and 20% at high intensity.
• "I think the buzz on the Internet comes from, this is what the best athletes in the world are doing... So, we should be copying what they're doing because obviously, it's working." – Prof. Gurd [08:38]

3. Practical Difficulties in Determining Zone 2 [09:11-10:56]

• Without lab testing (lactate measurements), it’s tough to accurately find one’s personal Zone 2.
• Common proxies (percent of max heart rate, ability to talk comfortably) are often inaccurate, especially across fitness levels.
• "Any sort of targeting a heart rate as a percent of max heart rate is probably not very accurate." – Prof. Gurd [10:08]

4. Is Zone 2 Special for Mitochondrial Adaptation? [12:00-13:52]

• Main finding from Gurd’s review:
  There’s no evidence that Zone 2 is uniquely or optimally effective for mitochondrial adaptation.
  • Adaptations occur, but not consistently; higher intensities provoke greater mitochondrial adaptations.
  • "Zone two training is almost certainly not the optimal intensity for inducing mitochondrial adaptation. If you want to maximize your mitochondrial adaptation, you want to target higher intensities of exercise." – Prof. Gurd [12:44]
• High-intensity interval training (HIIT) at around VO2 max is likely best for mitochondrial improvements.

5. Misunderstandings and “No Man’s Land” Myth [16:43-18:10]

• The idea that Zone 3 (between Zone 2 and higher intensity) is a “no man’s land” with little benefit is not supported by physiology.
  • In fact, increasing intensity generally increases adaptation.
  • The concept comes from elite athletes' need for strategic recovery—not general health-exercisers.
  • "If your aim is recovery, if you slip up into that zone three... now you're not recovering anymore... for most of us... we probably don't need to worry about that. In fact, we should actually be thinking about it the opposite way: we want to get above zone 2 as much as we can." – Prof. Gurd [17:36]

6. Fat Oxidation and Zone 2 [18:10-20:18]

• "The evidence... is probably in... favor of zone two... for promoting the ability to utilize fat." – Prof. Gurd [19:08]
• However, higher intensities also deliver improvements in fat oxidation; Zone 2 isn’t uniquely necessary.
• "You don’t have to do zone two training... you can also do higher intensities and still get improvements in fat oxidation." – Prof. Gurd [20:10]

7. Adaptations in Non-Athletes: VO2 Max and Fitness [21:12-22:16]

• Studies clearly show that, for the general population, higher intensity leads to greater improvements in VO2 max than Zone 2.
• Sacrificing intensity for more Zone 2 may reduce fitness improvements.
• "If we were to sacrifice intensity to do Zone two workouts, we're probably also sacrificing adaptations." – Prof. Gurd [22:08]

8. The Evidence Gap: Confidence vs. Data [22:47-23:35]

• The scientific literature on Zone 2 is surprisingly sparse, especially on health outcomes in average people.
• The Internet’s confidence is not matched by available research.
• "People on the Internet are very, very confident in how amazing Zone two is. And in the scientific literature there is not evidence that supports that confidence." – Prof. Gurd [23:20]

9. Potential Downsides of Over-Prizing Zone 2 [23:35-25:22]

• Over-focus on Zone 2, to the exclusion of other training, may mean missed benefits from higher intensity work—especially in VO2 max, the strongest predictor of all-cause mortality.
• "If you’re sacrificing high intensity... replacing it with Zone 2, you may be sacrificing improvements in VO2 Max, which... is pretty clear to be important." – Prof. Gurd [24:48]

10. When and For Whom is Zone 2 Useful? [26:23-28:55]

• For beginners or those needing recovery, Zone 2 (or walking) has value, especially for making activity accessible.
• Context matters—a marathoner’s Zone 2 is a run; a beginner’s is a walk.
• "If we're actually telling people... you have 30 minutes to exercise, but you need to be in zone two, that means you're just going for a 30 minute walk as opposed to doing a 30 minute jog... the benefits are going to be better from the jogging, right? Not walking." – Prof. Gurd [26:50]
• Occasional Zone 2 is useful for active recovery or days when the body needs less stress.

11. General Recommendations for Exercise [29:36-30:39]

• Main advice: Prioritize intensity, within individual limits/preferences.
  • Use intervals if possible—they’re hard, but highly effective.
  • However, anything is better than nothing, and preference/adherence comes first.
  • "Push yourself, go hard, accumulate as much high intensity volume as you can in your week... If all you want to do, if all you enjoy doing is walking, that's amazing... Zone two is great if it's something you enjoy doing. It’s just if we get into that question of what's optimal, that's where we want to start pushing intensity and getting away. Avoiding Zone two probably." – Prof. Gurd [29:36, 30:10]

Notable Quotes & Memorable Moments

• On Zone 2 Hype Vs. Science:
  “People on the Internet are very, very confident in how amazing Zone two is. And in the scientific literature there is not evidence that supports that confidence.” – Prof. Gurd [23:20]

• On What Actually Matters for Health:
  “Any exercise is good, any physical activity. The biggest decrease in mortality risk happens when you start doing something. So the difference between nothing and something is much larger than something and even more.” – Prof. Gurd [14:44]

• On Making Training Practical:
  "If you're telling people you have 30 minutes to exercise but you need to be in zone two, that means you're just going for a walk as opposed to a jog... the benefits are going to be better from the jogging." – Prof. Gurd [26:47]

• On Day-to-Day Choices:
  “If your body’s not ready for more stress, you want to avoid high intensity. That might be a place for Zone 2 training in the general population.” – Prof. Gurd [27:58]

Important Timestamps

| Time | Segment Description | |-----------|------------------------------------------------------------------| | 06:24 | What “Zone 2” really means — physiology, lactate, definitions | | 08:15 | Why athletes use Zone 2; source of the hype | | 09:47 | Difficulties in self-determining Zone 2 intensity for individuals | | 12:00 | Debunking the “Zone 2 is optimal for mitochondria” claim | | 16:43 | The “no man’s land” myth about Zone 3/threshholds | | 18:10 | Fat oxidation, molecular signaling, and whether intensity matters| | 21:12 | When Zone 2 doesn’t lead to improvements (VO2 max studies) | | 22:47 | The evidence gap and misplaced confidence | | 23:35 | Potential negatives of over-emphasizing Zone 2 | | 26:23 | For whom Zone 2 is valuable (beginners, recovery) | | 29:36 | Prof. Gurd’s general recommendations for health & training |

Conclusion & Practical Takeaways

• Zone 2 is useful, especially for making exercise accessible, low risk, and enjoyable—but it’s not uniquely effective or optimal for health, mitochondrial adaptation, or fitness compared to other intensities.
• For maximizing adaptations, prioritize intensity within safe limits and individual constraints.
  • Interval training and higher intensities provide greater improvements in fitness and metabolic health, for most people.
• For beginners, adherence, enjoyment, and simply moving more are the most important factors.
  • “Move somehow every day. And make it enjoyable.” – Prof. Gurd [35:24]

Resources Mentioned

• Review Article: Storczyk, K., & Gurd, B. J. “Much ado about Zone 2” – Sports Medicine, 2025.
• Queens Muscle Physiology Lab: [Find online for more from Prof. Gurd and his team]
• Contact for Further Discussion: Christy Starstruck (active on social media, discussed in episode) [34:31]

This summary captures the scientific clarification, myth-busting, and practical wisdom offered by Prof. Gurd, enabling listeners or readers to make better-informed choices for health and fitness.