Cardiac muscle pumps the heart and is not under conscious, voluntary control. Skeletal muscle, on the other hand, is able to be controlled voluntarily. It is skeletal muscle that is responsible for creating movement in all parts of the body. First we will concentrate on skeletal muscle. Cardiac muscle will be discussed later when we deal with the heart and cardiovascular system.
Skeletal muscle accounts for forty percent of the weight of the average man.
In athletes, depending on the sport, the total weight of muscle may be far higher. Muscles are composed of multiple bundles of fibers. There is absolutely no way to increase the number of muscle fibers which exist in your body. What you are able to do, however, is dramatically increase the size and shape of the muscle fibers. Hypertrophy is best accomplished by overloading the muscle with work.