a. In some muscles, the fibers are quite long and parallel and extend the length
of the muscle (from attachment to attachment). This type of skeletal muscle is referred
to as a ribbon or strap muscle.
b. In other muscles, the striated muscle fibers are oriented obliquely between
the two tendons of attachments. Such muscles are said to have a quadrilateral
c. If the striated muscle fibers appear to be attached to one tendon in a feather-
like arrangement, the muscle structure is known as pennate.
(1) If all of the fibers are on one side of the tendon, the muscle structure is
(2) If the fibers are on two sides, the muscle structure is bipennate.
(3) If the feather-like arrangement is branched, the muscle structure is
5-12. EFFECTS OF FIBER PATTERNS
Thus, ribbon muscles have long fibers. On the other hand, pennate (especially
multipennate) muscles have great numbers of short fibers. These different structures of
skeletal muscles affect both a muscle's relative strength and its distance of contraction.
a. Relative Strength. The strength of a skeletal muscle is proportional to the
cross-sectional area of its fibers. Therefore, a multipennate muscle is generally much
stronger than a ribbon muscle.
b. Distance of Contraction. On the other hand, the longer the fibers of a
muscle, the greater will be its distance of contraction. As a very loose rule of thumb, a
skeletal muscle can contract to three-fifths of its resting length. The ribbon muscles
(such as the rectus abdominis M., which flexes the trunk) have long distances of
contraction. The multipennate muscles have the least distance of contraction (but are
very strong and stable).
5-13. SOME BASIC PHYSIOLOGY OF THE SKELETAL MUSCLES
a. Length-Tension Curve. In paragraph 5-5c, we described the length-tension
curve for a striated muscle fiber. A length-tension curve can also be constructed for a
whole skeletal muscle. However, the FCT fibers of the skeletal muscle provide an
additional component to the tension produced by the muscle fibers. As the muscle is
extended beyond its resting length, the tension produced by the FCT fibers becomes
greater and greater. Thus, the tension produced by a whole skeletal muscle increases
greatly with increased length.