Muscle cells produce ATP anaerobically during periods of rapid exercise. ATP is the energy needed for cellular activity to occur. Generally oxygen is used to produce ATP in a process called aerobic respiration. When oxygen is not available to break down the carbohydrates that enable muscle contraction, the body continues to create ATP through anaerobic respiration. Anaerobic respiration results in less ATP production and in the waste product lactic acid.
Adenosine triphosphate is an energy carrier. Removing one of the phosphates from ATP creates adenosine diphosphate (ADP). The process of removing one phosphate releases energy. This energy is used by the body to carry out all cellular functions.
The process of making ATP begins with the breaking down of glucose. The first step in this process is glycolysis. Glycolysis occurs in the cytoplasm during both aerobic and anaerobic respiration. If oxygen is present, the process continues and is completed in the mitochondria, creating an abundance of ATP. If oxygen is not present, the process continues in the TCA cycle. This anaerobic process creates only 5 percent of the energy created when oxygen is present. When muscle cells exhaust their oxygen supply, they must use anaerobic respiration to continue to function.