[Scott Johnston]

Christian:

How prescient of you!  I addressed just this question in last night’s book group lecture. I think your mental model is good.  As mathematician George Box said: All models are wrong (meaning that they are not perfect representations of reality), but some are useful.

Glycolysis and its resultant pyruvate production occur in the cell’s cytosol outside the mitochondria.  A process of converting it to acetyl-coA allows it to pass through the mitochondrial membrane and get used in the Kreb’s cycle for aerobic metabolism.

Glycolysis can and will take place in the full spectrum of muscle fiber types.  The faster the FT fibers the more they will rely upon glycolysis and the less mitochondrial content they have.  Thus they are less endurance endowed.

Yes, one of the main goals of endurance training is to increase the mitochondrial content of faster and faster twitch fibers. Improving their endurance characteristics can provide propelling force for longer before fatiguing.  As you point out.  This moves the AnT upward in terms of power output.  You can run faster for longer (i.e., more endurance).

The vacuum analogy is a perfect example of George Box’s little ditty. The vacuum is comprised of: mitochondria in those same muscle cells where pyruvate is being produced, more remote mitochondria, the liver, and the heart.

While the fibers do apparently exist along a continuum thing of the slower twitch fibers acting as the vacuum for the next level up the FT scale.  This is what I talked about in the book group’s second physiology chapter. I think it will help you.  But you essentially have it, at least at the macro level we need to understand it.

Scott