Super interesting interview. So aside from mitochondrial benefits (or lack thereof) what would you say are the primary benefits of z2 for a general health population?
When I’m in a marathon build I’ll hit around 8 hours per week of running (plus 2-3 days in the gym) and formerly I had only been doing one or maybe two days above z2. This has me rethinking that, especially at my relatively lower volume and especially for cross training (maybe a bike or elliptical session could add in some z3-4).
Curious how this information has changed your approach to training or health, if at all!
Greg, I did 3 marathons in the top third of my age group as a 40 year old 190 lb. raw vegan- on only 8 miles a week as two runs of my "fast 4", plus one fast 10 per year to set my target marathon pace (one minute more), and a 20 mile shakedown a couple of months before. I fully agree with your relatively low volume.
Currently, I am 60 and my primary calibration activity is a weekly ruck of 3.5 miles with 30.3 kilos at a 4 mph pace. During the week, I do a muscle HIIT using bands, which seems like the most efficient to me, and a yoga workout mainly followed by dead hangs, each about 20 minutes. I don't have or feel the need for hours of Zone 2.
I would encourage you, for all the reasons, to add a bit of muscle, especially resistance HIIT, and HIIT in general, and keep your volume low for time efficiency and injury avoidance.
This is such a great episode and now has me questioning everything and I have so many more questions. I really want to do a deep dive on this and in particular for highly trained/experience amateur runners.
I drank the Zone 2 juice for years (and I still do from all the people like Dr. Peter Attia, Phil Maffetone, Matt Fitzgerald, etc.) but the amount of respected run coaches that are so angry at this is interesting. More to come - watch this space! (Also posted this as a restack)
Thanks Daren! It’s a very nuanced discussion and I hope the conversation didn’t come off as “don’t do zone 2.” The divide seems to be what to prescribe for gen pop vs. the highly trained athlete.
If the beneficial adaptations come from training in zone 3 and above, why do elites do so much training at zone 2 and below? wouldn’t they be better off swapping it for resting?
I think this comment is where the hardcore amateur athletes (me!) get confused and spend too much time doing zone 2. We see the pros with all their time and resources, and we want to mimic them. But it sounds like we should possibly have a totally different approach to zone-based/intensity-based training for goals like 5k-marathons.
The issue is that I did zone 2 for so long after having a weak aerobic base in my 20s that heavily limited my 800m potential, and I've seen some amazing gains across the board in health and fitness markers for the last 14 years. So, to discount zone 2 and the benefits I've gotten is pretty silly, but the fact that Kristi can't find evidence that zone 2 increases mitochondria and there are no studies showing this, is wild.
Again, I'm still trying to formulate a hypothesis, but I'm intrigued and annoyed all at the same time by this. That's a good thing.
Would lifting lighter weights more slowly for longer time cause muscle growth? The analogy might not be perfect, but it seems to me that we only grow through intensity. Long and slow is a kind of survival mechanism, not a growth mechanism.
I just thought that based on your question, so it's very fresh, and I reserve the right to be wrong.
Great interview! I am of the opinion that - as you alluded - there’s too many undefined Zone “protocols”. There’s 3 Zone models, 5 Zone, 7 Zone, and more. What would be considered Zone 2 in a three Zone model may be VASTLY different from Zone 2 in a seven Zone model; or not! It all depends on how things are defined. There needs to be a consensus for researchers as to which model is to be considered “standard” for research purposes, and what parameters define the Zones being discussed/investigated.
NO!! You *cannot* assume that! Most studies detail what they’re using to define each Zone, but there’s no standard. You’ve got to dig into the weeds of each study to see what parameters they’re using.
Not only is there no standard defining what Z2 is, research shows there’s very few markers which can be used reliably across a population to determine whatever threshold may be used.
“Results: Analysis revealed substantial variability in Z2 markers, with the coefficients of variation (CV) ranging from 6% to 29% across different parameters. Ventilatory Threshold 1 (VT1) and maximal fat oxidation (FatMax) showed strong alignment, whereas fixed percentages of HRmax and blood lactate thresholds exhibited wide individual differences.
Discussion: Standardized markers for Z2, such as fixed percentages of HRmax, offer practical simplicity but may inaccurately reflect metabolic responses, potentially affecting training outcomes. Given the considerable individual variability, particularly in markers with high CVs, personalized Z2 prescriptions based on physiological measurements such as VT1 and FatMax may provide a more accurate approach for aligning training intensities with metabolic demands.”
Is the exercise science community at a point of ‘settled science’ on the best practices for training for endurance sports?
The general physiology and skeletal muscle bioenergetics structures and processes seem to fairly well understood. How to stimulate them for adaptation and training effects seem to be understood. Why is there debate or conflicting studies at this point?
Good question Bill. I agree that - from a molecular POV - we understand what causes certain adaptations and how best to train for them.
Here's why there's a debate (IMO) - we're talking about two different goals. Coaches arguing with people in the longevity/general health space about the "best way to train." There's bound to be disagreement even though I'd argue we're tilting at windmills.
Thanks! This study and your talk really explains everything so well. I have been thinking about this for a while now: Is this intensity distribution simply an artifact? And we should really be careful with prescribing this distribution to the general public.
Super interesting interview. So aside from mitochondrial benefits (or lack thereof) what would you say are the primary benefits of z2 for a general health population?
When I’m in a marathon build I’ll hit around 8 hours per week of running (plus 2-3 days in the gym) and formerly I had only been doing one or maybe two days above z2. This has me rethinking that, especially at my relatively lower volume and especially for cross training (maybe a bike or elliptical session could add in some z3-4).
Curious how this information has changed your approach to training or health, if at all!
Greg, I did 3 marathons in the top third of my age group as a 40 year old 190 lb. raw vegan- on only 8 miles a week as two runs of my "fast 4", plus one fast 10 per year to set my target marathon pace (one minute more), and a 20 mile shakedown a couple of months before. I fully agree with your relatively low volume.
Currently, I am 60 and my primary calibration activity is a weekly ruck of 3.5 miles with 30.3 kilos at a 4 mph pace. During the week, I do a muscle HIIT using bands, which seems like the most efficient to me, and a yoga workout mainly followed by dead hangs, each about 20 minutes. I don't have or feel the need for hours of Zone 2.
I would encourage you, for all the reasons, to add a bit of muscle, especially resistance HIIT, and HIIT in general, and keep your volume low for time efficiency and injury avoidance.
Congratulations and Best of Luck.
This is such a great episode and now has me questioning everything and I have so many more questions. I really want to do a deep dive on this and in particular for highly trained/experience amateur runners.
I drank the Zone 2 juice for years (and I still do from all the people like Dr. Peter Attia, Phil Maffetone, Matt Fitzgerald, etc.) but the amount of respected run coaches that are so angry at this is interesting. More to come - watch this space! (Also posted this as a restack)
Thanks Daren! It’s a very nuanced discussion and I hope the conversation didn’t come off as “don’t do zone 2.” The divide seems to be what to prescribe for gen pop vs. the highly trained athlete.
If the beneficial adaptations come from training in zone 3 and above, why do elites do so much training at zone 2 and below? wouldn’t they be better off swapping it for resting?
Great question. I don’t think they’d be better off resting because there ARE benefits to the lower-intensity training.
I think this comment is where the hardcore amateur athletes (me!) get confused and spend too much time doing zone 2. We see the pros with all their time and resources, and we want to mimic them. But it sounds like we should possibly have a totally different approach to zone-based/intensity-based training for goals like 5k-marathons.
The issue is that I did zone 2 for so long after having a weak aerobic base in my 20s that heavily limited my 800m potential, and I've seen some amazing gains across the board in health and fitness markers for the last 14 years. So, to discount zone 2 and the benefits I've gotten is pretty silly, but the fact that Kristi can't find evidence that zone 2 increases mitochondria and there are no studies showing this, is wild.
Again, I'm still trying to formulate a hypothesis, but I'm intrigued and annoyed all at the same time by this. That's a good thing.
Could it be related to other aspects? Does z2 help with building more capillaries and tendon and ligament strength in a gentler way?
Would lifting lighter weights more slowly for longer time cause muscle growth? The analogy might not be perfect, but it seems to me that we only grow through intensity. Long and slow is a kind of survival mechanism, not a growth mechanism.
I just thought that based on your question, so it's very fresh, and I reserve the right to be wrong.
Great interview! I am of the opinion that - as you alluded - there’s too many undefined Zone “protocols”. There’s 3 Zone models, 5 Zone, 7 Zone, and more. What would be considered Zone 2 in a three Zone model may be VASTLY different from Zone 2 in a seven Zone model; or not! It all depends on how things are defined. There needs to be a consensus for researchers as to which model is to be considered “standard” for research purposes, and what parameters define the Zones being discussed/investigated.
Is it a safe assumption that most of these studies are referring to the 5 zone model?
NO!! You *cannot* assume that! Most studies detail what they’re using to define each Zone, but there’s no standard. You’ve got to dig into the weeds of each study to see what parameters they’re using.
Not only is there no standard defining what Z2 is, research shows there’s very few markers which can be used reliably across a population to determine whatever threshold may be used.
“Results: Analysis revealed substantial variability in Z2 markers, with the coefficients of variation (CV) ranging from 6% to 29% across different parameters. Ventilatory Threshold 1 (VT1) and maximal fat oxidation (FatMax) showed strong alignment, whereas fixed percentages of HRmax and blood lactate thresholds exhibited wide individual differences.
Discussion: Standardized markers for Z2, such as fixed percentages of HRmax, offer practical simplicity but may inaccurately reflect metabolic responses, potentially affecting training outcomes. Given the considerable individual variability, particularly in markers with high CVs, personalized Z2 prescriptions based on physiological measurements such as VT1 and FatMax may provide a more accurate approach for aligning training intensities with metabolic demands.”
https://pmc.ncbi.nlm.nih.gov/articles/PMC11986187/
OK! I *shall not* assume that!
Excellent ! I’ve been a hesitant/suspicious follower of the Z2 and 80/20 push, so this ameliorated some of my worries about pushing the boundaries.
Is the exercise science community at a point of ‘settled science’ on the best practices for training for endurance sports?
The general physiology and skeletal muscle bioenergetics structures and processes seem to fairly well understood. How to stimulate them for adaptation and training effects seem to be understood. Why is there debate or conflicting studies at this point?
Good question Bill. I agree that - from a molecular POV - we understand what causes certain adaptations and how best to train for them.
Here's why there's a debate (IMO) - we're talking about two different goals. Coaches arguing with people in the longevity/general health space about the "best way to train." There's bound to be disagreement even though I'd argue we're tilting at windmills.
Thanks! This study and your talk really explains everything so well. I have been thinking about this for a while now: Is this intensity distribution simply an artifact? And we should really be careful with prescribing this distribution to the general public.