Got it! And ultimately this is why people on Keto end up feeling miserable with this type of exercise, because the glycogen isn’t getting replenished? [/quote]
So basically now some fatty acids (even carbon number) end up undergoing beta oxidation to fuel most of our resting needs, and slowly replenish ATP from short bursts.
The odd chain fatty acids, and many of the amino acids, (particularly glutamine) can SLOWLY refuel glycogen by getting turned into glucose IN THE LIVER and then sent to the bloodstream. I think that several aminos can do this, but they get turned into glutamine first more or less.
And some of the amino acids turn into ketones. So 2 problems from sprinting on low glycogen: low blood sugar and ketones (which tend to reduce strength, and make blood acidic. This coupled with the fact that the glycogen you do have is making lactic acid can shut you down).
Again be mindful that a 10 second sprint is probably comparable to 3 times that long a period of performing a weight lifting set, like 30 seconds.
My estimate would be that between 1.5 to 6 seconds of maximal sprinting effort the body shifts into using glycogen because ATP is depleted. Its probably more like 5-25 seconds of performing weightlifting sets. In fact if you lift weights to the point where power decreases, or bar speed slows, it is a direct sign that ATP is starting to rely on glucose for replenishment. Again the Russians found generally max power could be maintained for 2-6 reps. If bar speed slows, if lactic acid is felt, you are past the maximal CP ATP power generation pathway which can be refueled by fat during short breaks.