Causes of fatigue

Given an adequate supply of fuel, hydration and electrolytes, what do we “run out of” that ultimately causes fatigue? Enzymes? Neurotransmitters? Oxygen delivery? Mental/emotional toughness? How does training work to extend time to fatigue and what gets replenished (besides glycogen) with recovery?

I really think this would be a good deep dive for Chad on a podcast, but I’m not sure how to get it there…

I feel like they’ve touched on it in some of the recovery segments by explaining the CNS responses to training stimuli. I don’t believe its about what we run out of, but rather how much stimuli we can handle before we need a break. Stress adds up, essentially.

I will say that a deep dive on the body’s physiological response to fatigue would certainly be interesting.

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I recently asked a bio scientist/athlete this, supposedly there is no definitive answer.

Fatigue is caused by depletion of anti-fatigue.


I’ve recently been thinking that what we run out if is “order”. Everything just gets slightly disordered, and at some point it affects performance. (This could also be called entropy increase). Energy is still there, but stored in the wrong places (looking at you, bellyfat). Equilibriums between different substances are slightly out. Some muscle fibres are damaged, and affect synchronisarion across bundles. Maybe some places have fluid accumulation that affects flow rates around it. The temperature is slightly off. Nothing is majorly wrong, but the accumulation of the little things becomes too much at some point.

Recovery is then a big tidy-up to bring everything back to normal. “Supercompensation” means improving some things, so they don’t run out that quickly next time.


See above about “no definitive answer,” but it is CNS related. Your governor kicks in and says No More.