[RoosterRedux]

I don't know what they mean here, but I have seen numerous studies that say that HIIT changes a body down to the cellular level, actually improving and even adding new mitochondria (improving autophagy), and possibly building new neural pathways.

I would suggest ignoring those details and just focusing on the results for your particular brain.

[tired&retired]

Aerobic ATP production in the mitochondria is 7 times more efficient than anaerobic ATP production in the cytoplasm.

Increased oxygen from exercise is a major factor in the Krebs cycle ATP production in the mitochondria.

Exercise increases O2.

When ketones are utilized as fuel in the mitochondria the production of carbon dioxide is decreased further enhancing O2 circulation and utilization in the body. (Krebs Cycle or Citric Acid Cycle Biochemistry)