Monday, September 25, 2023
Mitochondrial Health

Zone 2 Training: The Science Behind Peak Metabolic Health | Dr Inigo San Millan | The Proof Podcast

Zone 2 training has gained significant attention in recent years, with many people trying to integrate this incredibly beneficial type of exercise into their routines. But how do you know when you’re in Zone 2, and what are the mechanisms and benefits of this type of training? In Episode #277, I’m joined by Dr Inigo San Millan to clarify these questions and delve into the cardiometabolic science that makes Zone 2 training truly noteworthy.

👇 Visit The Proof website for the full show notes and supporting studies. 👇

With an illustrious career spanning twenty-seven years, Dr Inigo San Millan is a leading applied exercise physiologist and sports medicine advisor. He’s consulted for an array of professional teams and athletes globally, across multiple sports and organisations, including the US Olympic Committee and the International Cycling Union. Dr San Millan has been at the forefront of developing innovative methodologies in areas such as physiological and metabolic assessment, mitochondrial function, and nutrition.

A faculty member at the University of Colorado in the departments of Medicine, Human Physiology, and Nutrition, he applies his expertise beyond the athletic sphere to address metabolic rehabilitation in individuals suffering from chronic diseases like cardiometabolic diseases and type 2 diabetes. Renowned as a frequent speaker at global conferences, Dr San Millan brings an unparalleled depth of knowledge on metabolic health, making him an ideal guest to elucidate the science behind Zone 2 training.

Learn about the intricacies of Zone 2 training as we break down complex topics into digestible insights that you can apply to your own fitness journey. Dr San Millan provides a clear roadmap for understanding how energy is produced at various training zones, emphasising the unique benefits of Zone 2 and how to harness them for longevity.

Specifically, we discuss:
00:00 – Introduction
2:21 – Understanding Metabolic Health
6:40 – Metabolic Health Among Elite Athletes: Exploring the Perfection of Studying
8:00 – Metabolic Health, Mitochondria, and Nutrition
14:41 – Defining ‘Metabolise’
18:33 – Metabolic Flexibility
21:01 – Mitochondrial Dysfunction
24:44 – The Role of Oxygen in Energy Production Mechanisms
28:07 – Comprehending Energy Zones
40:27 – Energy Metabolism Mechanisms: Glucose vs. Fat
45:29 – Zone 2’s Optimal Stimulation of Mitochondria
51:12 – Lactate’s Impact on Mitochondria
1:00:03 – Managing Lactate Levels: Strategies Employed by Athletes
1:15:39 – Establishing an Aerobic Base
1:17:57 – Inducing Mitochondrial Stimulation Through Zone 2 Training
1:31:30 – Metabolic Health in Sedentary Lifestyles: Understanding the Impact
1:38:41 – Zone 2 Demystified: Unveiling Its Significance
1:40:39 – Recognizing Zone 2: How to Identify Your State
1:54:31 – Zone 2’s Role in Fat Loss: Separating Fact from Fiction
2:00:40 – Optimizing Zone 2 Intensity for Maximum Results
2:12:32 – Effective Modalities for Zone 2 Training: Making Informed Choices
2:18:53 – Resistance Training’s Integration within Zone 2 Regimen
2:21:12 – The Optimal Timing for Zone 2 Training: Navigating the Day
2:27:00 – Supplements and Their Relevance to Zone 2
2:38:59 – Amplifying Training Benefits: Embracing Zones 3 and 4
2:40:47 – Outro

Connect with Dr Inigo San Millan:
– Instagram:
– Twitter/X:

Listen to the episode we mentioned with Dr Herman Pontzer at

If you have any additional questions you would like answered in the future, let me know in the comments.

Optimise your health with InsideTracker’s biomarker analysis. Get exclusive access to InsideTracker’s new ApoB test, and a significant discount at

The best way to support the show is to use the products and services offered by our sponsors. To check them out and enjoy great savings, visit

Enjoy, friends.

Want to support the show?
The best way to support the show is to use the products and services offered by our sponsors. To check them out, and enjoy great savings, visit

• The Proof with Simon Hill –
• Book: The Proof is in the Plants –
• Apple Podcast –
• Spotify –
• Instagram –
• Twitter –
• Facebook –
• Plant-Based Ferments Guide –
• Two-week meal plan –
• Plant Performance –
• Use the products and services offered by our sponsors. To check them out, and enjoy great savings, visit


Similar Posts

46 thoughts on “Zone 2 Training: The Science Behind Peak Metabolic Health | Dr Inigo San Millan | The Proof Podcast
  1. I'm about to watch this – my favourite type of podcast! First, I feel compelled to say that I think the host is the healthiest and most glowing person I've ever seen (and I'm 57!) He exudes health and wellbeing. Impressive!

  2. I knew this would be the clearest summary of ISM's thoughts. Future questions!

    1) Does the modality of exercise have an impact? e.g. running or elliptical trainer would build mitochondria capacity in the whole body. Cycling mostly in the upper legs. Is one superior to the other? If not why not?

    2) As you get fitter doing Z2 is actually very taxing on the body. Stephen Seiler's work has shown that most athletes don't actually spend a ton of their time in zone 2, but rather Zone 1. ISM's thoughts on that? (I can link to a Twitter thread where Seiler mentions it if needed). e.g. for me I'm up to 250w on the elliptical and 8:00 min miles running. That's a ton of stress on the body at the volumes he's talking about for a non elite

    3) Intensity for duration. Seiler calls this extensify. Walking was mentioned a ton in this pod. Thru hikers who regularly do 20 miles a day get adapatations in vo2 max and resting HR that higher intensity zones do. There's clearly a point where low intensity but multipled by a huge volume can achieve the same. Zones are specific to a set duration. Your zone 2 wattage in hour 1 will certainly be Z4 at the end of hour 2 if you're not elite. What's ISM's views on that? The talk test doesn't work in these scenarios.

  3. The Hadza are not plant based, they are hunters primarily eat meat augmented by some raw honey and tubers. Dr. Saladino lived and study these people.

  4. i thought weight loss comes from being fitter and having a higher energy turnover at rest at a slight caloric deficit no matter what intensity trained at. getting fitter -> eating more -> higher energy turnover at rest -> (maintaining slight deficit) -> having no stress = fat loss (muscle gain)

  5. Great listen! I bought a treadmill specifically for JUST Z2 and have yet to use it for that. Oddly enough, I now enjoy hiking and run+walk on it as well as hiking bootcamp. Now I'm convinced I was right in the beginning and must incorporate Z2 into my workload. That many minutes will be unattainable though.

  6. I just found your channel and can't get enough of your videos. Very informative,. It looks like you aim to be as inclusive, thorough and impartial as possible. You also have the most insghtful guests. Top of their field. Thank you!

  7. At 1:59:00, Inigo says energy balance is more important to the very fit, while efficiency is for the over-weight. I see fit people keep their weights constant no matter how much they eat as they are already efficient at burning off the extra calories.

  8. Would you expect the use of stimulants to move the zone 2 range toward faster bpm’s? What might it mean if the talk test can be passed at 165-175 bpm’s with caffeine use? Without?

  9. Loved this episode ! @simonhill your summaries throughout are just golden and so helpful . I have had 3 FibBit Versa 3 which have all died after 3 months . I’m loathe to bother replacing the last one again (previous was replaced FOC). Would anyone recommend a Garmon ? If so which one ? I did find it motivating to see my Zone 2 minutes etc and a weekly log … kept me motivated. And yes maybe not super accurate … but really more than adequate. Any recommendations would be so helpful 🙏

  10. Good advice is supplements don't take if messes up other pathways. Too many supposedly supplements are being listed, trending, I will save my money eat real food. Glad 150 minutes a week is low as I walk hike hills hours DAILEY; likely in zones. RT I do daily as I remember being on a farm in the countryside which was a natural active 7 days a week lifestyle. Enjoyed this discussion with a passion. Thankyou both. Please another podcast, part 2.❤

  11. I’ve watched and rewatched most of the Zone 2 podcasts published. I have the theory down now but what would be really helpful is a short demonstration with Iñigo watching and commenting on the demonstration. Because the margin for error is relatively small (10 bpm) it would be good to see what he means by the ‘talk test’ indicator. Thanks for adding to this growing area of knowledge.

  12. Simon, please help me find your interview of Herman Pontzer. What is the title? I've read his book Burn and have watched multiple interviews with him and learn something new from every one. Thanks! Just found your channel and am becoming a subscriber 😊

  13. This was a really interesting topic, and you both were awesome at reviewing and summarizing the information. Thanks to both of you for sharing your time and expertise ❤

  14. do you motherfkers really have to talk for 2hrs42mins ? Just do a 10 min chat that goes thru all the important need to know info. no one actually cares about the intense science shit

  15. Edit…touching on it at the 2:15:00 mark. Does it matter what type of exercise you are doing as it pertains to the mitochondria adaptions? Is it as simple as mitochondria doesn’t care what your doing…all about heart rate. As example, if I’m indoors doing a long zone 2 on elliptical or long zone 2 run outside? I’ve never gotten a clear answer on this.

    To go a step further, are some exercises better for mitochondria development?

  16. Thank you guys for this. It is priceless. Your gratitude towards one another at the end of the video is wholesome. And you deserve the credits. You're changing lives with this content Simon, and Iñigo it is really admirable that you dedicate yourself to sharing your knowledge through the divulgators like Simon or Fissac in Spain, we're lucky to have access to such scientifical wisdom.
    I've been taking notes and I think it was all very clear. If I ever have any doubt, I'll make sure I'll share them with you guys in case you meet again 🙂
    Bless you!

  17. hey Simon, would you consider doing a follow up to this episode with Dr Stacy Sims? I have been listening to some of her recent content and, unless I have misunderstood, I think she has a perspective on zone 2 for women in the menopause transition, leading up to or post menopause. Her perspective is for women in this life stage to polarise their training – a focus on heaving lifting but then polarising this with sprint interval training and/or true HIIT. She discourages the moderate intensity cardio but I'm not sure if this extends to zone 2 also (not sure if she buckets these together)? I just wonder for women in the menopause transition who already have elevated cortisol, does zone 2 training for 150-300 mins a week exacerbate this and drive up other unwanted symptoms such as abdominal weight gain? Would be great to get her perspective. Thank you, great episode as always!

  18. Hello Simon, I have been following your channel for quite a time now. At the moment my ApoB is 68 and LDL is 30 HDL is 27 and triglycerides are 103. My HbA1C is 4.4. My fasting blood glucose is under 80.
    I am eating a whole food plant based diet. But my main issue is whenever I am eating fully plant based my platelets and MPV blood marker shoot up which typically indicates that u will have a clotting disorder in near future. But when I am easy on plants and fruits combined and add a little bit meat or fish or nuts then I tend to do better. So what can I do to have both good HDL and better and thin blood while being plant based. Need your true honest advice on that

  19. I actually listened to your interview of Dr Stacy Sims before this one and now I'm a bit confused. She doesn't seem to be in favor of zone 2/moderate intensity cardio for women, especially that many hours a week. I don't know if this whole conversation only applies to men because the studies were done on men and excluded healthy premenopausal women as they often do, or what do you think Simon? Is this something that's gonna be covered in a future episode?

  20. Great discussion tying together many different fields of interest (biochemistry, metabolism, mitochondrial function, sports medicine, ICU recovery).
    I deep dove into his publications last night.
    Definitely a podcast to listen to multiple times.
    Thank you for the update on the lactate shuttle.

  21. GREAT CONVERSATION. Best podcast i've ever watched on the subject. Dr Iñigo is so interesting and humble. And the questions were perfect. Congrats

  22. Simon, he spoke about the recovery time needed following exercising in a higher zone for a few minutes and returning to zone 2. He said to add more time to the workout to allow for that or to just make our zone 2 minutes consecutive if possible. But is that also true when we downgrade to zone 1 and then return to zone 2? That was not clear to me and with hiking that typically occurs. Love your podcast and so glad I found it!

  23. Great and valued information about zone 2. I need to add cycling on stationary bike to get to at least 300 hours a week. I am curious if 60 minute yoga session translates to zone 2? Because it's mainly isometrics there is increase heart rate. Still with 120 minutes of yoga a week, it helps boost that minimum hourly requirement for optimal benefit.

  24. Simon, in your podcast with Paul Taylor last year, he recommended 1-2 30-min Zone 2 sessions per week (60 min) whereas Dr. Inigo recommends atound 300 minutes of Zone 2 cardio per week. Im quite confused. Is the latter more applicable to more athletes?

  25. Hi Simon, my brother has debilitating chronic fatigue syndrome. According to PsychSceneHub’s article, people with CFS have mitochondrial dysfunction, so I’d imagine Zone 2 would be incredibly helpful for this.
    My question – how long does it take (and at how many hours a week) for these mitochondrial benefits to set in?
    He does have a ton of friction with starting to exercise, so any information I can show him might help
    Thanks again!!

  26. Man, I am hoping this information will help me pick the lock of my training for martial arts. Just started 2 years ago, currently 46 years old, and just can’t figure out of how make more significant improvements in my endurance during sparring. I think building this zone 2 base vs thinking I can just power through until I get better (likely in my high end zone 4 or greater) might be the change I need.

    Also, your line of questioning during the interview was very much what I wanted to ask as I was listening. This episode is another gem, thank you as always!

  27. This was very interesting. Should I conclude that in order to increase my stamina, I should not go for short bursts of everything I have, but instead for longer duration zone 2-ishness? And does it mean the bursts are useless? Say on a bike?

  28. Yet another excellent episode, TY.
    As a TOFI T2D, I'd rather stay in Zone 1 until and unless the visceral fat completely dissolves, and only then upgrade to Zone 2 because for a hyperlipidemic state like diabetes, that level would most probably be too much of a mitochondrial strain and inevitably induce considerable lactate production…

  29. Dr San Milan is very persuasive I have to say. But he is asking a lot. Not even Peter Attia in his Centenarian Decathlon asks so much of his patients in terms of time in Zone 2. He mentioned that sustainability in exercise and diet is important and everyone would agree. But wow! 600 minutes plus per week plus Zone 5 plus resistance training. Thank you Simon for exploring breaking it up into two 30 minute sessions. That seems much more sustainable especially if it is broken into two modalities to keep exercise interesting. Thank you as always for an informative and beneficial podcast.

Leave a Reply

Your email address will not be published. Required fields are marked *