The waste product is lactic acid lactic acid: A toxic chemical produced during anaerobic respiration rather than carbon dioxide and water: glucose → lactic acid (+ little energy) Muscle fatigue. Muscles become fatigued (tired) during long periods of vigorous activity. This means that they stop contracting efficiently. read more
An aerobic cycle may produce between 36 and 38 ATP molecules, while anaerobic respiration only creates 2 ATP molecules. Since muscles often run out of oxygen during extreme exertion, anaerobic respiration keeps them running. In animals, including humans, the anaerobic cycle produces lactic acid, which causes muscle cramps. read more