White and Red Fibers

Animals move in two basic ways. They move suddenly, rapidly, and briefly, for example when a startled pheasant explodes into the air and lands a few hundred yards away. And they move deliberately and persistently, for example when the same pheasant supports its body weight on its legs as it stands and walks; or a steer stands and chews its cud. There are two basic kinds of muscle fibers that execute these movements, the white fibers of pheasant and chicken breasts, and the red fibers of bird and steer legs. The two types differ in many biochemical details, but the most significant difference is the energy supply each uses.