Uhhh cellular respiration is used all of the time, while running you just need more oxygen, and when your cells can't get they they start doing anaerobic resp. or fermentation which creates lactic acid that can cause muscle fatigue.
Uhhh cellular respiration is used all of the time, while running you just need more oxygen, and when your cells can't get they they start doing anaerobic resp. or fermentation which creates lactic acid that can cause muscle fatigue.