The skeletal muscles are very responsive to use and disuse. With virtually all types of training muscles undergo an actual enlargement of the cells, with an increase in the number of protein filaments in the myofibrils of each muscle cell. Aerobic exercise will produce some enlargement but a weight training program will induce full muscular growth.

By the same token, neglect of muscular conditioning will result in a gradual decrease in size and strength of the skeletal muscles. In an extreme case, such as when a limb is in a cast for a very long time, the muscle fibers disintegrate and are replaced by connective tissues.

In fact our muscles are constantly growing and shrinking. They juggle between growth or breakdown depending on the nutritional status at any time. For example, growth will often occur if sufficient protein is ingested at a meal. Muscle breakdown occurs in between meals if additional protein is required for the production of antibodies or enzymes.

Protein deposition (muscle growth) can be important in losing weight fast because it affects our metabolism. As stated above, there is more protein breakdown between meals so if a dieter hardly eats in order to lose weight then more protein will be lost from muscle cells resulting in a lowered metabolic rate. A high metabolism is a must if you wish to lose fat weight quickly!