Muscle metabolism is a general term used to describe the complex biochemical reactions involved in muscle function and development. The body takes in nutrients to provide energy, which must be broken down by different body systems to replicate cells, remove waste, fight infections, and perform other processes needed for life. Regarding muscles, various amino acids, carbohydrates, and lipids must either be broken down to use as energy or made by the muscle cells in order to build healthy muscle mass. Collectively, these processes are called muscle metabolism.
Humans have three different types of muscle systems: cardiac, smooth, and skeletal muscles. Each of these muscle systems serves a different purpose and, therefore, has slightly different requirements for function and development. Discussions of muscle metabolism, however, most often refer to the skeletal muscle system. Skeletal muscles are attached to bones and are responsible for locomotion. Building skeletal muscle mass is known as muscle anabolism, whereas the loss of muscle mass is known as muscle catabolism.
To more accurately understand the processes involved in muscle metabolism, it is first necessary to understand the general principles of metabolism. In short, as an individual takes in food, the body uses a sequence of enzymes to break down food into various chemical components and sends them along metabolic pathways. These metabolic pathways are similar to highways, bringing raw chemical components to each body system for further processing. Once each system receives these raw chemicals, it selects certain molecules to use as energy, while other molecules are used to create new chemicals or new cells. Catabolism refers to breaking down molecules to release energy, whereas anabolism refers to using molecules as building blocks.
All muscles, including skeletal, cardiac, and smooth muscles, use some form of muscle metabolism to release energy, form new muscle cells, and remove waste or toxins. For skeletal muscles, the specific process and the biochemicals used in each process varies. What chemicals are used and the steps involved are based on the type of muscle fiber and whether muscle mass increases or decreases.
Increasing skeletal muscle mass, for example, requires the addition of more muscle cells to thicken each fiber or develop more muscle fibers. Accomplishing this means the individual muscle cells must, through physical activity and various biochemical reactions, reduce myostatin and increase cytokine, the hormones responsible for regulating muscle growth. Additionally, amino acids, carbohydrates, and lipids are used for energy and as building blocks to produce more muscle cells. Alternatively, if myostatin increases, cytokine decreases, or if there is insufficient carbs, amino acids, or lipids, muscle metabolism operates in reverse to thin or reduce the number of muscle fibers.