What is the limiting factor for aerobic performance in trained athletes?

I can imagine it could be one of several things:

1) The ability of your heart/lungs/main arteries to absorb and transfer oxygen.
2) The ability of your working muscles to absorb this oxygen.
3) The efficiency with which your working muscles use the oxygen.
(others?)

I'm curious about the answer in general, but one reason I am asking is that
I have a large difference between my seated and standing FTP (with standing FTP higher) and I'm wondering what could cause this. For example, is my standing FTP limited by (1) but my seated FTP limited by (2) or (3)?

Also, is there a good current (scientifically current) book that I can read on this stuff?

You can stand on a bike for an hour?

VO2 Max.

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I've thought about this too and I think it's a combination of:

1. Large lung capacity to take in large amounts of oxygen
2. Efficient lungs that allow transfer of oxygen to blood
3. High level of red blood cells to transfer oxygen to muscles
4.Efficient muscles that absorb oxygen quickly and tnasfer waste (lactic) away.





Basically, the whole process of getting oxygen from the outside air to the muscles and getting rid of waste, has to be efficient.


For example, Christophe Moreau had a huge lung capacity, but an average hermatocrit level (red blood cell level), which menat he was never a super champoin or Tour de France winner.

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VO2 Max.

My understanding is that for most well-trained athletes for longer durations, the most probable limiting factor is the stroke-volume of the heart.

Perhaps in some theoretical sense, but heart stroke volume is one of the fastest adaptations an athlete achieves. You get almost all your heart volume increases in the first six to eight weeks of steady training. It can take years after that point to develop the capillary and mitochondrial densities which yield continued increases in sustainable power.

Like the other guys have said, VO2 Max is generally considered the limiter. But VO2 Max relies on just about everything mentioned in the OPs list. And even if you manage to hit some genetic limit of your VO2 Max in terms of gas exchange rates you can still train to sustain higher percentages of your VO2 Max power at your FTP and even increase your power at VO2 Max with continued training.

-Dave

I would have commented the same, if the question would have been what limits VO2max. Primarily stroke volume of the heart. Not that other factors don't influence VO2max and performance, just that in terms of differences between individuals from what I've seen difference in stroke volume most likely explain the largest part of the variability. My impression is that cyclists don't differ to a great degree in gas exchange parameters or muscle efficiency.

IOW, if you take a group of cyclists all equally well trained and had to predict their finishing order in a 40k TT based solely on physiologic parameters. The one that would do the best job would be stroke volume.

How's that if there is a large variance in the amount of red blood cells in the blood?
It's no coincidence that the greatest increase in cycling performance in recent years has been the introduction of EPO. It's no good having a big stroke volume if the blod you are pumping isn't as oxygenated as it could be.

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I don't disagree with the theory, but I'm pretty confident in saying that hematocrit is poor predictor of performance. In fact it usually drops with training because of other factors that expand the plasma. IOW, a bunch of cat. 3s and pros likely wouldn't differ terribly in their hematocrits, they would differ to a large degree in the stroke volume of their hearts.

Yes. Mostly anyway (maybe sit here and there for a short rest).

That sounds sensible to me, though in my case there's obviously something else limiting my seated power (since 300w standing is not hard for me but it is hard for me seated).

How much is stroke volume trainable? I remember reading that V02 Max is not very trainable.

Also, what features of your muscles limit aerobic power? Is it something about muscle type or is it more to do with the amount of blood that gets in there?

Quite a bit, but it happens very early in the training process and isn't dominant in terms of long term improvements. That's the point I was trying to make in my previous post. If you're talking in a purely theoretical sense then the ability to pump more blood per unit time might be considered very important. But in a practical sense heart stroke volume increases very quickly during the first couple of months of training and then the heart stops enlarging.

The important long term and continual improvements to aerobic fitness revolve around increasing mitochondrial densities in the working muscles, increased capillary bed densities around the working muscles, recruitment of type IIa muscle fibers, increased glycogen storage and other adaptations. Most of these long term adaptations are in and around the working muscle groups and are not central as in changes to the heart or lungs. Sure if you can deliver more O2 per unit time for instance with increased red blood cell count or with EPO that can give an athlete a substantial boost in performance but the muscles still have to be able to use the O2 along with fuels such as fat, glycogen and lactate to produce energy. High mitochondrial densities are the key there.

Thinking has changed over the years on that point. VO2 max in terms of increased gas exchange is more trainable than previously thought. More importantly, power at VO2 Max and sustainable FTP as a percentage of VO2 Max is highly trainable. Two athletes with the same weight could both have a VO2 Max of say 80 ml/kg/min but one might have an FTP of 350 watts and the other 400 watts. In the end it's that sustainable power that really counts and the second rider who can utilize a higher percentage of their VO2 Max for sustained efforts will have a big advantage.

-Dave

Is your saddle too low?

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Hello LAnierb,

1.Pretty much all are wrong when it comes to a competitive athlete.VO2max and aerobic metabolism are a very old concept and a myth. I have seen Pros with average VO2 (both absolute and relative) and being great riders on the road and even the lab and viceversa. Don´t worry, Vo2 max is not "the limiting factor".
2.Your muscles will extract all the O2 needed for the most part. O2 is almost entirely bond to hemoglobin (Hgb) 4 O2 per Hgb, and with the action of 2,3,DPG is released to the cell. However, not even under the most intensity exercise Hgb unloads the whole 4 O2´s adhered to it.
3. It is the efficiency of muscles to utilize fuel (CHO and FFA) and deal with glycolysis by-products (Lactate), acidosis, pi..etc..what really makes the difference.

It is not at the cardiorespiratory level, neither at the circulation level...it is at the cellular level and all that happens there what makes the different in this sport. You can have an amazing VO2max (I have seen many) and develope huge power (also seen many) but then at the cellular level, you are very poor adapted to use fuels efficientely and on the road you are just an average rider. Same can happen the other way around.

Hope it helps,

Cheers.

Thanks for the answers. This answer seems more consistent with my experience I have to admit (though that doesn't mean it's right). Is there a good reference book for this stuff or is it all still in papers?

Can you post some examples of who you mean by 1. (if not by name then by sample race performance level, e.g. Grand Tour top 10) and what you mean by "average".

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