A muscle has become fatigued when it cannot continue muscular contractions at the same rate despite nervous system stimulation. A variety of situations may cause muscle fatigue that differ depending on the intensity of muscular activity. After high intensity exercise like sprinting a 100-meter dash, the skeletal muscle depletes the ATP and CP stores and lactic acid begins to buildup. Exhaustion of energy stores paired with a drop in acidity from lactic acid buildup creates muscular fatigue. Another example of fatigue includes activity at a moderate intensity over a long period of time, like running a marathon. ATP demands can keep up through aerobic metabolism over the course of a few hours during an endurance event like this, but if the
