Final answer:
ATP (C) is the molecule that does not accumulate during muscle fatigue; it is consumed and its levels decrease. Lactic acid and inorganic phosphate, on the other hand, can build up and contribute to fatigue.
Step-by-step explanation:
The molecule that is NOT thought to accumulate during muscle fatigue is C. ATP (adenosine triphosphate). During muscle contraction and fatigue, ATP is rapidly consumed, and its levels typically decrease, rather than accumulate. The process of muscle contraction requires ATP, and once it is utilized, it is broken down into ADP (adenosine diphosphate) and an inorganic phosphate.
On the other hand, other by-products like lactic acid and inorganic phosphate may build up during anaerobic metabolism when the muscle is under strenuous exercise and the oxygen supply is insufficient, leading to the feeling of fatigue. Moreover, creatine phosphate provides energy initially, and glycogen is used subsequently to produce ATP anaerobically, a process that results in the production of lactic acid.