What do muscles require large amounts of to sustain energy conversion from glycogen?

Muscles require large amounts of oxygen to sustain energy conversion from glycogen during physical activity. When muscles engage in exercise or any strenuous activity, they utilize glycogen as a primary energy source. The process of breaking down glycogen into glucose and subsequently converting that glucose into ATP (adenosine triphosphate), the energy currency of cells, necessitates oxygen.

This aerobic process occurs in the mitochondria of muscle cells, where oxygen helps in efficiently converting glucose into energy, especially during prolonged, steady-state exercise. In the absence of sufficient oxygen, muscles may rely on anaerobic metabolism, which is less efficient and leads to the production of lactic acid, resulting in fatigue. Therefore, the presence of oxygen is crucial for optimal energy production from glycogen, making it the correct answer in this context.