If a marathon runner experiences a sudden, sharp decrease in performance around mile 20, which failure mode is most likely contributing to this 'hitting the wall' phenomenon?

💡 Explanation

Muscle fatigue during intense exercise such as marathon running leads to glycogen depletion; because glycogen is the primary fuel source for sustained muscle contraction, its exhaustion impairs ATP production by aerobic respiration. Therefore, the runner 'hits the wall,' rather than benefiting from cortisol (which is already elevated) or sparing glycogen, both of which would delay this failure.

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