The white meat of a chicken’s breast is composed mainly of fast-twitch fibers. The muscles are adapted to contract rapidly for a short time but fatigue quickly. Chickens normally do not fly long distances. They spend most of their time walking. Ducks, on the other hand, fly for much longer periods and over greater distances. The red, or dark, meat of a chicken’s leg or a duck’s breast is composed of slow-twitch fibers. The darker appearance is due partly to a richer blood supply and partly to the presence of myoglobin, which stores oxygen temporarily. Myoglobin can continue to release oxygen in a muscle, even when a sustained contraction has interrupted the continuous flow of blood.