They exhibit a great deal of resistance to fatigue, and are suitable for maintaining sustained contraction. Red fibers predominate in the muscles of the limbs. They are also found in the intrinsic muscles of the back responsible for maintaining erect posture. While white fibers fatigue faster than red fibers, they are capable of generating large amounts of tension over a short period of time. This makes them ideally suited for rapid, precise, fine movements.
White fibers predominate in the digits and extraocular muscles of the eyes.
White fibers are more generously innervated than red fibers. Many muscles of the body have fibers whose size, and myoglobin and mitochondrial content lie somewhere between the extremes of red and white fibers. They are appropriately called intermediate fibers . Cardiac muscle - Found in the heart and the bases of the large veins that supply the heart. Unlike the syncytial organization of skeletal muscle, cardiac muscle is composed of individual, branched cells lying parallel to each other with central nuclei.