Abstract

During exercise, a steady supply of energy (adenosine triphosphate [ATP]) is essential for the ATP-dependent processes that are associated with skeletal muscle contractile activity and exercise as we know it. Metabolic energy-producing pathways in the muscle cell involve both substrate-level phosphorylation, or anaerobic metabolism, without the need for oxygen, and oxidative phosphorylation to constantly replenish the required energy. The fuels that are used to meet these energy needs include phosphocreatine and carbohydrate in the glycolytic pathway to generate anaerobic energy and primarily fat and carbohydrate to produce aerobic energy in well-fed individuals. The relative contribution of these pathways is determined primarily by the exercise intensity and the duration of exercise, but is also affected by training status, preceding diet, age, gender, and environmental conditions. Optimal substrate availability, provision, and utilization before, during, and after exercise is critical for maintained exercise performance. This chapter provides a brief overview of energy provision, fuel use, and the regulation of skeletal metabolism during varying exercise intensities and durations. Activation of the energy-producing pathways in skeletal muscle for the provision of ATP for very intense exercise for short periods of time or lower rates of ATP production over longer periods of time is closely related to the regulation of muscle contraction itself and the by-products associated with the use of ATP. Remarkably, the combination of the aerobic and anaerobic energy-producing pathways working together from the onset of exercise allows for the impressive physical performances in exercise and sporting situations that can be achieved.