I have some exercise physiology questions

First off, I love TR and it has absolutely made me faster, so know that these questions come out of love from a fan. But I have been consuming media and information outside of the TR ecosystem, and it has brought about some questions.

1.) Is there a trade-off between VO2max and aerobic efficiency?
2.) Is there a role for a 2-3 hour ride in Zone 2 on the weekends that no interval workout can replicate, particularly in terms of mitochondrial efficiency?

I just finished a podcast interview between Dr. Peter Attia and Alex Hutchinson, PhD, both of whom I consider much smarter than I with some interesting opinions on sports physiology. I would love to see an interview with Dr. Hutchinson on the TR podcast, discussing the mental vs conventional physiologic parameters as limiters to performance.

From Dr. Attia’s perspective…
Does exercise dose have a J curve, when plotted vs mortality? Is there a difference between exercising for performance (the F1 race car) vs exercising for longevity (the sedan than can go over 500,000 miles)? Is there a downside, from a cardiac perspective, when you take your HR up to its maximal zone, hold it there, recover, and repeat, over and over and over again, in terms of fibrosis, hypertrophy and potential for arrhythmia?

And finally a quote from Dr. Hutchinson:
“A runner will never run as fast as they are capable of if they don’t do interval training. Also, a runner will never run as fast as they are capable of running if they only do interval training.” Agree or disagree?


I just watched the utube version for my 2 hr zone 2 ride. Race fitness and health/longevity are two different things, and at the elite level I suspect that the former actually harms the latter, the example being given by Peter Attia of TdF participants. I think since we all are an experiment with N=1, it’s hard to say how much training is harmful. In my former life, I trained and raced while holding down a very stressful job, and succumbed to a stress related autoimmune condition. Ended my cycling career until retirement. Now I train for fun and fitness, mindful not to dig too deep-mostly.

Thanks for the response. This is what I’m kind of getting at. I had a couple of episodes of chest pain when doing run intervals last year. I’m awaiting my echo test at the end of this month. I don’t think its going to show much, but wanted to get it checked out anyway. But I am starting to wrap my mind around getting away from exercising for performance and more towards health and longevity.


At 66, I managed to get a stress test (no symptoms), to make sure I could forge ahead with VO2 max hard start intervals. They kicked my but, but no cardiac problems.

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I think a lot of us have discovered the trade off of too much high intensity intervals in terms of stagnation in performance (or worse) and the effects it has on the rest of life (chronic fatigue). The debate is how much interval work is appropriate and of course changes on an individual basis, and changes depending on the training phase, age, training history. One of my big realizations for me, personally, was that less is definitely more in terms of HIIT training, and that finding the time to increase volume has been the ticket.


Higher intensity exercise tends to be associated with all-cause mortality risk.


Oops! Left out the word “lower”!!

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What is “aerobic efficiency”?

What happened to me I think is quite common for endurance trained people and I don’t know if it is related to early mortality, but I once had an ECG needed to enter a gran fondo, my GP said it looked as if I was having a heart attack right there.
I then went to a sports cardiologist specialist and after an effort test with ECG and and echography of the heart he concluded I am good to go.
Nevertheless it left me thinking if endurance sports are all that healthy after all :sweat_smile:

But don’t different types of efforts affect the actual heart (as a muscle) differently? Isn’t it that low intensity endurance (z2, on a 5-zone scale; z1 on a 3-zone scale) makes the muscle bigger where as higher intensity interval type work makes it “thicker” ?!

Don’t remember where i heard about this… one of the half dozen podcasts i listen too.

aerobic efficiency => the ability for the mitochondria to utilize oxygen effectively. Think about a big V8 engine’s horsepower vs its fuel efficiency. (Don’t know if that’s an accurate analogy)

What I understand by efficiency: the mechanical energy you get from the chemical energy stored in carbs, fats and proteins.

You’ll have to define what you mean by “effectively”, then, because I still don’t know what you mean.

Yes there is a roll for zone 2 rides in terms of Mitochondrial biogenesis that intervals can’t replicate…and of course if 2-3 hours is what you have then that’s great but I think it really starts to kick in around 4 hours+ if you have the time :grinning:

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Interesting; thanks for that dose. I was trying to be conservative with the time-crunched athlete. A lot of our internal (my buddies) discussion revolves around what is ideal vs what is practical for busy individuals. So I appreciate the info that in order to get that mitochondrial response, you need to allocate 4+ hours for the Zone 2 ride.

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I couldn’t find a great resource for aerobic efficiency, but here is something. It can be measured by dividing output (power on the bike or speed on the run) by input (heart rate).

Everyone who has ever exercised has died… I guess it’s time to stop. :wink:

Considering most of us have sedentary jobs and limited time to train, I sort of doubt we approach the point where exercise/training on TR crosses over from being healthy to being extremely harmful to a point where people should give up training (at least for most folk).

Outside of occasional ramp tests, an 3-4 hours of moderate to intense exercise is probably the least of our worries from a health perspective. I might change my tune if the leading cause of death was exercise and not health problems related to lack of exercise.

For professional athletes, the risk is real since these folks are often willing to push their bodies to the absolute limit, play while sick or hurt, or take risky health decisions.

I also think the thing with any sport is figuring out where the risks/gaps are and addressing them. For example, addressing imbalances, bone mass and maintaining muscle mass through weight training to offset some of the negatives from cycling - but the same could be said for every sport.

That final quote seems to echo the whole polarized vs. intensity thing that’s been going on for a bit.

FWIW - Interval training can include intervals at a lower intensity. You could train for an interval of 60 minutes at Z2 and recover for 5 mins at Z1. I don’t see interval training as being the same as HIIT.

I also think most folks on TR don’t only do intervals, we train so that we can do better at group rides, enjoy longer fun rides, events… etc. So if the point is people need to do longer rides, etc… odds are it’s being done and I don’t think there’s much dead horse left to beat in the regards.

What is needed for most folks is figuring out how to structure your training to get results.


I agree with 99% of this, especially the parts about diversifying the exercise experience and training with goals in mind (hanging with the group). My concerns are with the “build” phase when my HR gets up into the low 180s during the interval. My volume is nowhere near what even most people on this forum are at. But my intensity and effort in a given interval, given my fitness level, is every bit as intense as anyone else.

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I tend to tap out when my heart rate hits 165 honestly, but I think my Max HR isn’t very high… 170’s estimated… or maybe I’m just the type to back off at that point.

I think this is a tough spot, because either the TR user has to make the call about their limit and wonder if they are getting a benefit of leaving it on the table, or push and assume their body can handle it. Sounds like to get more certainty, you’d have to talk to a doctor or coach.

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Seems like a made-up term to me, kinda like Friel’s “decoupling”. Why not just call it what it is, rather than pretending to have discovered or invented something new?

In any case, since VO2 is proportional to pace or power, and is the product of SV and O2 extraction, then no, there wouldn’t be a trade-off between “aerobic efficiency” and VO2max. Just the opposite, in fact, i.e., you would expect them to change in parallel. This of course is the basis for the Astrand-Rhyming test for predicting VO2max that used to be commonly offered in YMCAs, etc.

My understanding is that aerobic efficiency isn’t a new concept, albeit new to me.