Energy systems question

Hey guys,

I’ve heard on the podcast a few times that energy systems (aerobic, anaerobic and PC) are a series of sliders. I went looking for answers but got lost in deep weeds so thought I’d ask to see if any of you have the answer.

I read that aerobic metabolism can produce 34 molecules of ATP from one molecule of glucose. I also read that anaerobic metabolism can produce just 2 ATP molecules per molecule of glucose.

SO my question is when I’m doing an all out sprint am I working with 36 ATP per molecule of glucose or is the aerobic ‘slider’ turned down at these maximal levels? Is there a relation ship between the anaerobic ‘slider’ coming on and the aerobic ‘slider’ coming down or does the aerobic system stay pinned?


Probably visual will be easier (chart from WKO), contribution of aerobic and anaerobic systems at given power:

So there is interplay between two of them.

But all out sprint effort is somewhat different:

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The other difference is, rhe anearobic system produces those 2 ATP fast. The aerobic system produces much more, but is much slower.

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Isn’t FTP below VO2max? So how can everything above FTP be anaerobic?

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I assume you’re referring to the graph, not the article, since the article doesn’t mention FTP? In which case it’s kind of confusing at first (and I have no idea how WKO derives the data for the above graph, I assume from metabolic carts on their athlete sample) - but you have to add up the green and blue shaded areas to reach the red line (the modelled Power Duration Curve) - so whilst the green shaded area is indeed below the dashed orange line (modelled FTP), if you look for example at the point where there’s supposedly equal contribution from both energy systems around 30 seconds, that’s well above mFTP but its still saying ~50% comes from aerobic power.

Yes, I was looking at the graph, which labels FRC as anaerobic and FTP as aerobic. That can’t be right, because FTP is below VO2max, and only above VO2max do you have to rely on anaerobic metabolism.

That’s not my understanding - I thought glycolysis (which is anaerobic metabolism, yeah?) occurs even when at-rest. Admittedly my understanding is all pretty much second hand knowledge, but I managed to find some stuff through Google scholar that seems to me to agree with this, for example, this relevant extract from Role of oxygen in regulation of glycolysis and lactate production in human skeletal muscle:

Operative words are “have to”.

Also, since it requires your whole body to generate power at the pedals, it really only makes sense to consider the system in its entirety.

Ok sure - semantics aside, I’m not sure I understand what you’re getting at then - the graph shows anaerobic contributions dropping off rapidly over log-time, but never quite reaching 0%. Which given anaerobic metabolism occurs even at rest, and scales up 25x at just 40% VO2max, makes sense, no? It’s not saying the everything above FTP is anaerobic, it’s saying that the higher you go above FTP (which means the less time you can sustain such a maximal effort), the more anaerobic metabolism contributes to power generation.

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No, I think it shows everything above FTP - that is, FRC - as being anaerobic, which is clearly incorrect.

It is definitely not saying that - in fact it’s saying for that person, even their 1 minute max power is predominantly aerobic - about 70% aerobic from eye-balling it. I agree it can be a confusing graph to interpret in just a screenshot though, particularly given they haven’t highlighted a particular time point so there’s no values displayed at the top.

The chart is labeled:

FRC (anaerobic)
FTP (aerobic)

However, since FTP is less than VO2max, and since only above VO2max can you be certain that anaerobic ATP production is occurring, this can’t be correct.

The bottom line is that the chart underestimates aerobic metabolism and overestimates anaerobic metabolism. Whoever designed it obviously doesn’t understand basic exercise physiology.

False, see article I quoted above. Glycolysis occurs below FTP as well, and even at rest. You can be certain it’s occurring as long as the subject is not deceased.

In what world is only 30% glycolysis at 1 minute max power overestimating anaerobic metabolism?

Again, you are confusing what happens in some cells or tissues with what happens on a whole body basis. Only if whole body lactate content is increasing can there be net anaerobic energy production. If lactate is not accumulating, then 100% of whole body ATP production is due to oxidative phosphorylation. To claim otherwise would require violation of the laws of thermodynamics.

As for the chart, the logic behind it is clearly incorrect regardless of the quantitative values it spits out.

Yes without marker it is hard to interpret. Here is the marker. FRC power is extensive anaerobic according to iLevels and FTP is aerobic contribution. In WKO VO2 max is called FRC/FTP.

And for values - the dashed line is a value so for example (in my case with different chart data than this) 2 min power is 75% aerobic, 5 min power 88%. So they do not overvalue anaerobic that much.

That first chart is amazing. Even at the top of my local steep climb when I am bleeding from my eyeballs the anaerobic contribution is tiny? Also if I want to break ten minutes for that climb (my project for this winter) I want my aerobic fitness as high as possible and should not just be training using high intensity intervals.

Thanks for posting.

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Yes. That is why cycling is an aerobic sport :slight_smile:
High intensity intervals are for activation your bigger muscles and you want them to work more aerobically.

I checked with Kolie, and the confusion is all yours my friend. Have a great day :blush:

Then Kollie is also confused.

External power is a product of the whole body, not just your legs (unless you think the latter can pedal for long on their own when disconnected from the heart, lungs, brain, etc.).

VO2, which measures the rate of aerobic energy production, and VO2max, which sets its upper limit, are also whole body measurements.

Thus, estimating the aerobic versus anaerobic contributions based on power and VO2 can only be done on a whole body basis. The fact that one tissue may be producing lactate while another is oxidizing it does not enter into the calculation, because all that matters is the net result.