During extended, intense exercise, a person begins to tire and breathe heavily. If this person continues to exercise, his muscles will soon switch from aerobic respiration to anaerobic (alcoholic) respiration anaerobic (lactic acid) respiration to aerobic respiration anaerobic (alcoholic) respiration to aerobic respiration aerobic respiration to anaerobic (lactic acid) respiration

Usually during exercise, unlike during rest times the muscle cells need to respire more. So they need more oxygen and glucose for energy and the carbon-dioxide produced as waste must be removed quickly. So when person gets tired or breathes heavily during intensive workouts means they are in need of more oxygen. So the cells starts performing anaerobic (lactic acid) respiration even though it releases less energy.