What are the different types of skeletal muscles?

There are two important types of skeletal muscle. Type I, also called slow-twitch, is composed of small fibers and is used primarily for carrying light loads. This type of fiber predominates in a runner who is very thin and whose body contains a lot of lean muscle. A marathon runner's leg muscles contain an abundance of well-exercised type I muscle fibers.

Type II muscle fibers, also called fast-twitch, are large muscle fibers used for lifting heavy loads. A weight lifter has an abundance of type II muscle fibers. Competitive sprinters also have plenty of type II muscle fibers in their large leg muscles, which are used to produce strong movements for a short time.

There are three types of muscle tissue found in the human body. There are visceral muscles, which consist of smooth muscle tissue, which is controlled by the autonomic nervous system and responds to both hormones and neural stimulation. Smooth muscles have no striations, as the nucleus is centrally located. Thus, they are involuntarily controlled. Also, there is cardiac muscle, which is only found in the heart and is also stimulated by neural activity and hormones. Lastly, there are skeletal muscles, which aid in the movement of the body and is mostly attached to bones by means of tendons. These muscles are striated, and are voluntarily controlled.  Skeletal muscles can further be sub-divided into two categories: red and white muscles. Red skeletal muscle tissue consists of a chemical not found in the white skeletal muscle called myoglobin. Myoglobin is a protein-like molecule, which aids in the storage of oxygen, which is essential to its function. Thus, this extra molecule is responsible for giving red muscles their coloring.