The word ‘anabolism’ is often associated with protein in the context of weight training. Anabolism refers to the energy-requiring chemical reactions that convert small, simple structures into large, complex molecules. Protein synthesis is an example of an anabolic reaction. The reverse process is catabolism.
With any weight-training programme which includes adequate protein consumption, the ultimate aim is for the body to adapt to the stresses of resistance training in an anabolic manner. In other words, for muscle fibre hypertrophy to occur. Muscle fibre hypertrophy is an increase in the size of muscle fibres, which make up the muscle tissue. It is this which causes as increase in muscle size. An important factor in achieving this is a balanced diet, including adequate protein consumption.
During resistance training, muscle fibres experience ‘micro-tears’ which are repaired and strengthened by protein. However, in order for this to occur, a complex series of biological processes, involving various structures and chemicals within the body, must take place. This cascade of events, otherwise known as ‘satellite cell theory of hypertrophy’, takes place within the skeletal muscle.
Skeletal muscle, the highly adaptable muscle that is connected to the skeleton and enables movement, consists of type I slow-twitch fibres and type II fast-twitch fibres. Fast-twitch fibres, as the name suggests, contract quickly but tire rapidly as they consume more energy. The enlargement of fast-twitch fibres is what constitutes to an increase in muscle size.
Satellite cells contain a single nucleus and are located on the outside of the muscle fibres. When the muscle fibres receive trauma, such as the micro-tears which result from resistance training, the satellite cells are activated and begin to multiply. The cells travel to the site of the trauma and fuse both to each other and to the muscle fibres. Some of these satellite cells donate their nucleus to the muscle fibre, which allows the skeletal muscle cells to produce more actin and myosin. Actin and myosin are tiny filaments, or myofilaments, which are found in the myofibrils- the subunits that make up each individual muscle fibres. Actin and myosin are responsible for the contraction and relaxation of muscle.
The activity of satellite cells is monitored by growth factors, which are hormones. Growth factors therefore play a major role in increasing the size of muscle fibres. There are a number of growth factors, each with various functions. One example is FGF (fibroblast growth factor) which aids muscle repair by synthesising new blood capillaries.
Another hormone which affects muscle fibre hypertrophy, is one that you will have heard of- testosterone. Testosterone activates the growth of muscle tissue by increasing the number of chemicals at the muscle fibre which are responsible for signalling.
Satellite cell theory of hypertrophy is still a vastly researched topic but from what is currently known, an increase in muscle size occurs from the synergistic relationship between satellite cells and a number of hormones, including growth factors and testosterone, all of which are proteins.