The major factor leading to exhaustion during exercise is the depletion of glycogen in the muscles.
Glycogen is a complex carbohydrate molecule that serves as a storage of energy in animals.
Glycogen is used during cellular respiration to produce ATP, the energy coin of the cell, and thus perform physical exercise.
This carbohydrate is produced by mammalian organisms (including humans) in order to store energy when required.
In conclusion, the major factor leading to exhaustion during exercise is the depletion of glycogen in the muscles.
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