According to the Fayette County Public Schools, the breakdown of adenosine triphosphate (ATP) in a chemical reaction with water provides energy for skeletal muscles to contract. Since the amount of ATP stored in muscles is small, metabolic pathways that generate new ATP must be activated for continued muscle contraction. These pathways are either anaerobic (in the absence of oxygen) or aerobic (in the presence of oxygen).
According to class notes from Montana State University-Bozeman, ATP is synthesized from adenosine diphosphate (ADP) with energy provided by creatine phosphate, anaerobic glycolysis or oxidative metabolism. During high intensity exercise, creatine phosphate within skeletal muscle is broken down. Creatine phosphate resynthesizes ATP anaerobically. Staff notes from Fayette County Public Schools state that the phosphate in creatine phosphate can be transferred to ADP to form ATP in a process called substrate phosphorylation.
The Fayette County Public Schools point out that another anaerobic process is glycolysis. Glycogen stores within the muscle supply glucose which is metabolized to yield lactic acid during short bursts of high-intensity exercise. Glucose is also available in the blood. Glucose undergoes glycolsis to produce ATP rapidly. Oxidative metabolism is an aerobic metabolic pathway that uses carbohydrates, fats and proteins. Oxygen is available in the blood or from the protein myoglobin. Aerobic metabolism produces 36 ATP, and 2 ATP is obtained from anaerobic metabolism.