Weber claims that only a small fraction of the O2 in arterial blood is extracted by muscle “even under hard exercise”. This is simply false - in fact, during maximal exercise, almost ALL of the available O2 is extracted by exercising muscle, e.g., femoral venous O2 content will be close to ZERO.
That’s a pretty fundamental misunderstanding. In fact, I’d say that it is rather shocking.
ETA: Gawd, it’s like watching a train wreck…in the very next breath, he claims that O2 uptake by muscle, not delivery by the heart, is the “bottleneck” limiting VO2max. This is the opposite of reality, i.e., the capacity of muscle to take up and utilize O2 exceeds the ability of the heart to pump blood, such that VO2max is primarily limited by convective O2 delivery.
I… thought you were joking that he said that. His misunderstanding may be that measured between the coronary artery and vena cava typically there’s “only” a 40-60% difference, but that’s because the blood that’s been depleted of O2 across the muscle bed has been mixed with blood going elsewhere. He also mentions that the bottleneck is the muscle extraction, which is simply not the case. I’ve already got a response in this episode for O2 extraction, and WD#21 for a little more info on the pO2 dynamics.
Do you mean the difference between arterial and coronary sinus blood? Extraction by the heart typically runs ~60%, and doesn’t change (much) with exercise. Between arterial and vena caval (actually, you have to go all the way to the pulmonary artery before mixing is complete), extraction is only about 25% at rest, but rises to 75-95% during maximal exercise.
I heard “most people” and did not hear him say “trained athletes” - would that make a difference? Assume “most people” = untrained or recreational athlete.
With only 5 years of riding, why do I see good gains after taking an off-season break and restarting with a lot of aerobic endurance and then laddering up to threshold over 3-5 blocks? Moderate volumes, say ramping 5-6 hours/week to 8-10 hrs with a peak of 12 hours? Also seen a strong response to doing low cadence tempo. Averaged across the years, my training volume has been pretty low - maybe 5 hours/week.
I’ve got an engineering background and never took a physiology or biology class in college. Struggled to follow your podcast so went looking for answers. This pic made a lot of sense to me, as an engineer:
mm mercury measures the partial pressure, not actual o2 usage but ok. And trying to chase down normal oxygen consumption by muscles here is one search term “average oxygen content of venous and arterial blood” and trying different search terms I find stuff like this:
Cardiac output and arteriovenous oxygen difference are the two factors that determine the overall oxygen uptake. At rest 5 ml of the 20 ml of oxygen in every 100 ml of blood is extracted, producing an arteriovenous oxygen difference of 5 ml. During exercise blood flow to the tissues increases, and haemoglobin dissociates more easily; therefore the arteriovenous oxygen difference widens during exercise. With aerobic training the tissues become more efficient at taking up oxygen; therefore the arteriovenous oxygen difference is still greater in trained individuals.
No book covers it sufficiently, or none that I’ve seen anyway and I have quite a few that touch on this in some way or other. Some papers out there measure femoral O2sat as low as maybe 5-10%. pO2 in cells at FTP is about 3-4 torr, and there’s very little inhibiting O2 diffusion so the flux is as needed. The reason not all O2 is extracted from the blood is obviously equilibration between tissues and blood and there’s no active mechanism to get out more, but mostly that not all tissues are maximally respiring. If we did have all circulating blood passing through maximally respiring tissue, the venous pO2 would be about 1 torr.
If we were actually limited by extraction, oxygen vector doping would be useless. In fact, if we look at untrained vs trained individuals, O2 extraction difference is pretty low, say about 80% for untrained and 90% for trained (whole body). We even see very poor correlations between vo2max and avo2diff (0.2 or 0.3 R^2 iirc). But VO2max and Qmax for untrained is 50% that of those trained. This is the opposite of what we would expect to see if utilization were the limiting factor.
I’ll see if I can dig up a good review paper somewhere. If you want to look for one or just any study, I bet you’ll find some good ones by Calbet or Montero.
But why do 80% of people say they stop the ramp test because their legs get tired, and only 20% say it’s due to heart/breathing reaching the limit? Need to HTFU?
well when you can’t get enough oxygen in your cadence will drop. then your legs will give out soon after. but the point where your cadence drops significantly is where you should end it for an accurate measurement
Peter Wagner and Russ Richardson (who trained with him) have also done a lot of work in this area.
Really, though, it’s been known for over half of a century that O2 supply, not utilization, is the limiting factor. This raises the following questions:
why does Weber believe otherwise, and
what might this say about the validity or interpretation of VLamax, etc.?
It comes from a cart before the horse understanding of metabolic pathway regulation that has downstream effects that go all the way to training types. And oftentimes when those principles go well, it’s a figuratively true, literally false kind of situation, where you train in such a way that there are the expected results, but the actual reasons they happen are different from the assumptions. Validity of vlamax is kiiiind of a thing, but again, for different reasons than assumed due to incorrect interpretations of regulatory mechanisms.
Let us all take a deep breath (pun intended ), it is clearly not a very scientific video. As @empiricalcycling wrote, from a black box perspective what is not wrong, O2 goes in, and a significant amount of O2 comes out. If there was nothing to improve in that box, we’d have no peripheral VO2max adaptations. What is unfortunate, he concentrates on them, as if there was no or only little room for central adaptations.
Except that a significant amount of O2 doesn’t come out of the legs at VO2max, even in an untrained person. This is a fundamental misunderstanding on Weber’s part. It is the sort of error in thinking that leads to people, e.g., wasting time doing one-legged pedaling drills to try to get faster.
What I don’t understand is, If Weber has got it so wrong how is it that Jumbo Visma, who utilise INSCYD and, I believe, use Weber as a consultant, seem to be getting it so right?
I don’t know. Maybe talent? Drugs? Luck? They don’t actually pay any attention to Weber? Who the heck knows.
What can be said is that he is dead-wrong about something that anybody who has ever taken an undergrad ex fizz class should understand. That makes me question every assertion he has ever made.
), it is clearly not a very scientific video. As 