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Old 06-13-2008, 01:00 PM   #19
Steven Low
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Re: Is phosphagen system the primary system of crossfit training?

Sigh. You definitely know your physiology, but I think you're confusing it a bit. While I may have been slightly exaggerating on some counts (which I tend to do often here for the sake of argument), there's some things here that need some clarification it seems.

P.S. Damnit, you and I write too much. Had to break this post up into two parts cause I hit the word limit.

Originally Posted by Phillip Garrisonq View Post
I think you're confusing how the various metabolic systems work. Unless one is a highly trained endurance athlete, it generally takes approximately 90-120 seconds of work before one moves substantially into the aerobic system. Furthermore when you are doing work at a very high intensity (above 85-90% of MHR) the bodies ability to provide oxygen to the muscles and tissues cannot keep up with the bodies need for ATP, the body then reverts back to substrate level phosphorylation by fermenting pyruvate into lactic acid to maintain proper ATP levels.

No, I don't think it's the case for just highly trained endurance athletes. If we look at untrained vs. trained subjects, the untrained subjects are obviously going to have substantially lower PCr and glycogen stores while they will also have lower enzymatic markers for glycolysis, TCA and mitochondrial dehydrogenase markers. Training with quick burnout of intramuscular glycogen stores (HIIT/tabata/etc.) tends to show increased markers in pretty much all pathways even those with fairly short interval.

Take a look at this study wfs

400m is around 40% aerobic... which is under a minute. I think that is a large enough contribute that we can consider that aerobic takes quite quickly during high intensity exercise within a minute don't you think?

As for maximum intensity exercise, yes accumulation of lactate is true. While some does go into the bloodstream via lactate transporters to go back to the liver for resynthesis into glycogen, the vast majority is still within the muscle that it can be used as a source of fuel for the body to reconvert to pyruvate for TCA and oxidative phosphorylation when the enzymes are available.

Yes it's true you move gradually from one energy system to the next. but becuase of the complex mechanisms involved, and the rapid need for ATP from the high intensity nature of many WOD's when doing high intensity bouts of under 2 minutes in duration, you're mostly taxing the PC, and glycolytic systems.

Hmm, covered this above with that study.

Short intervals like Tabata, are not aerobic at all, they are almost completely anearobic in nature. The aerobic system is not designed to handle phosphyrlation for very high intensity work such as wind sprints, Tabats, etc. Due to the many complex steps of Oxidative Phosphorylation (TCA Cycle, ETC, ATPase complex) one cannot develop the ATP fast enough via this system to maintain work levels. The evidence that you are not working mainly in the Aerobic system is evident by the usual burning sensation accompaning the intervals, which is a result of large quantities of pyruvate being fermented to Lactic Acid.

Again, this is simply not true.

This tabata experiment though you may take fault that it's 7 minutes long and done with rats (which is approximately ~2 tabata intervals with the way CF handles them) shows significant increases in HAD (3-b hydroxyacyl-CoA dehydrogenase) which are comparable to *6 hours* of low intensity swimming.


The aerobic system is the energy pathway of low to moderatly high intensity work (resting hr to 85-90% of MHR). The surest way to know you are not in the aerobic system primarily is burning in the muscles due to lactic acid accumulation.

Okay, this is where you turned "more" wrong. High levels of lactic acid accumulation DO NOT necessarily mean that there is very little oxidative phosphorylation going on. Remember, we still have TCA enzymes working overtime (obviously the accumulation is of pyruvate is too high for the pyruvate dehydrogenase to handle), but the TCA and oxidative phosphorylation are definitely still working.

The main point that needs to be made here is that glyoclysis is only providing 2 ATP per turnover. With the excess accumulation of lactic acid, obviously there's going to be a lot of turnover and thus glycogen is going to be providing a substantial amount of energy. However, TCA/oxidative phosphorylation provide one ATP (well, GTP) per turnover plus 3 NADH and one FADH2 per turn which results in what.. uhh 3*3 + 2*1 = 11 ATP per turn. Even though we have this pathway turning over less, again, still a significant amount of energy is being produced by it during maximum intensity.

Let's also take into account that NAD+ and FAD coenzymes do not have 100% of their concentration in the cytoplasm (some will be in the mitochondria for oxidative), so to say that the excess NAD+ is being used for glycolysis (when obviously there's limitations to the amount of enzymes in muscles for the amount of glycolysis as well) is a poor argument.

In examination of high intensity exercise, there's mobilization of fatty acid stores from high catecholamine output (catecholamine output increases as intensity increases) as well as increases in interleukin-6 (also increases linearly as intensity increases). Fatty acids, as you know, dump directly into TCA/oxidative pathways so they are a good indication of oxidative phosphorylation.

Breathing hard is not a good marker of aerobic pathway. While sitting at your desk, you're primarily using the aerobic pathway. By comparison, after running 200 meters at all out speed, you're breathing rate will increase rapidly, yet you are not utilizing the aerobic pathway at all. The rapidly increased breathing is a result of the body attempting to expunge hydride Ions from the blood, not necessarily to get oxygen into the system.

Okay, I was kinda flying by the seat of my pants and suggesting that rate of breath has to do with oxygen consumption. Obviously, partially true sometimes. But for the most part fairly true in this case.

Aerobic is still utilized in 200m albeit to a lesser extent.

Why are there hydride ions in the blood though? CO2 + H2O <-> H+ + HCO2-. This is how the body regulates blood pH by ridding itself of CO2 so that blood pH does not drop too fast. Why is there significant increases in CO2 in the bloodstream? Pyruvate dehydrogenase along with the rest of the TCA/oxidative phosphorylation are responsible for the accumulation of CO2.

Obviously, there's some oxygen already available to muscles through myoglobin within muscle cells which starts to get used up very rapidly which is why rate of breath tends to increase to not only dump out excess CO2 but to get more oxygen in to fuel oxidative phosphorylation.

The main point here that I'm trying to make is that the cardiovascular system is integrated fairly extensively with the muscles especially regarding aerobic activity (like the VO2max tests suggest). Therefore, extensive increases in rate of breathing are *generally* related to increases in oxidative phosphorylation.

The aerobic system requires that the body slow down, to keep up the demand for High energy phosphate groups, with the ETC and atp synthase complexes ability to provide them via oxidative means. To illustrate this example, look at the split times of the 400, vs the 800 meters. An elite level 400 meter sprinter will run the distance in under 45 seconds. An elite level 800 meter runner will run each 400 meters in slightly more than 60 seconds. At the end of the run, both runners will be breathing quite heavily, but for different reasons.

Hmm, covered this with the above study. And no, not different reasons... it's because 400m and 800m are both aerobic to different extents. One just hurts more than the other (800m).
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