Let's focus on skeleton muscle cells. So skeleton muscle cells are the cells that use ATP to basically contract the act of mice and filaments. And that allows voluntary motion. So I can move my arm because of skeleton muscles or I can sprint across the room because of these skeletal muscle cells. Now, skeleton muscle cells have the option of using aerobic or anaerobic respiration. So if there is oxygen present, it will use aerobic, but if not, it will use anaerobic.