- It has to do with it in the sense that there is a finite amount of pyruvate and lactate that can be present in the cell and still have it working properly.
The first part in metabolism of glucose (including glucose derived from those amino acids that are capable of conversion to glucose) is the glycolytic pathway, which can generate ATP extremely rapidly but does not completely burn the glucose. Instead the end product is pyruvate, which is interconvertible with lactate.
As a side note, fats cannot be used in the above process.
The second part is the Kreb’s cycle, which completes the burning and leaves no problematic residues. The end products are just CO2 and water. This metabolism however is limited in its maximum rate. It cannot produce energy at anywhere near the maximum rate of work output that a muscle is capable of.
Now if the rate of glycolytic metabolism is no faster than the Kreb’s cycle is running at – because demand for work rate is within the capacity of those two processes working within the maximum speed of the Kreb’s cycle – then there is no ongoing buildup of lactate. Work can be conducted at such a rate for a long time.
However, if the work rate exceeds this, as for example in sprinting, unavoidably levels build up as the Kreb’s cycle cannot keep up.
That’s doable for brief periods only, till levels become as much as tolerable.
There is a slight oversimplification in the above as a given muscle can lose lactate to the bloodstream and it can be taken up and used elsewhere in the body, but the general principle still applies.
That is a means of allowing a moderate over-run of the glycolytic pathway vs the Kreb’s cycle within a given cell but still doesn’t support lengthy work output at energy output levels such as the glycolytic pathway can support when going all-out.
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Long periods of work at the lactate threshold are in the category of long hard aerobic work. Not the way to be lean and preserve muscle.
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VO2 max is mostly genetic. The trainability is not really large in any instance. Just as a personal guess I would think HIIT effective at improving it, where there’s still room for improvement, but don’t know of data on it. There must be some though.
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Aerobic metabolism (using oxygen, which the Kreb’s cycle does) and anaerobic metabolism (glycolysis) occur simultaneously in any instance. However if the rate of glycolysis is no faster than that of the Kreb’s cycle then we call that aerobic overall.
The only way that a 400 meter sprint can be performed aerobically is if it’s run at a speed modest enough to be sustainable for miles. If actually sprinted then while the Kreb’s cycle is going all out, the glycolytic (anaerobic) process is going far faster yet and so it’s overall called anaerobic.
A competitive athlete running it properly most certainly can’t sustain the speed significantly longer, for the reasons above.