Dance Anatomy & Kinesiology

The Muscular System 41

the biceps brachii, pectineus, adductor brevis, and
the very long and thin sartorius muscle.
In contrast, with penniform (L. penna, feather +
forma, form) or pennate muscles, fibers run at an
angle relative to the muscle’s longitudinal axis as
seen in figure 2.5B. This diagonal arrangement,
similar to the design of a feather, allows more fibers
in a given volume of muscle (greater physiological
cross-sectional area) and hence the ability to produce
greater force. However, since these fibers tend to be
shorter and are also at an angle to the long axis of the
muscle, a 50% shortening of a fiber in these muscles
results in less shortening of the muscle as a whole.
So greater force production is gained at the cost of
reduced speed and range of motion. Approximately
three-fourths of the muscles in the human body
follow this penniform arrangement, including many
muscles of the limbs such as the gluteus maximus,
quadriceps femoris, deltoid, tibialis posterior, and
gastrocnemius.

Muscle Attachments to Bone.

Connective tissue, including the endomysium, peri-
mysium, and epimysium, is intimately related to

muscle tissue and is key for providing form and for

attaching muscles to their respective bones. As shown

in figure 2.6, individual muscle cells are covered by a

very fine sheath termed the endomysium (G. endon,

within + mys, muscle), while bundles of about 100 to

200 muscle fibers (fascicles) are covered by a dense

connective sheath termed the perimysium (G. peri,

around + mys, muscle) and the whole muscle itself is

covered by another membrane called the epimysium

(G. epi, upon + mys, muscle). The central part of a

muscle, which tends to be thicker and in which the

contractile cells predominate, is called the muscle

belly. Toward the ends of the muscle belly, the

muscle cells end; but the connective tissue cover-

ings continue to attach the muscle to one or more

bones: directly (e.g., trapezius, figure 2.7A), via a

cordlike or flat band called a tendon (e.g., biceps

brachii, figure 2.7B), or via a sheetlike structure of

fibrous tissue called an aponeurosis (e.g., latissimus

dorsi, figure 2.7C). Tendons (L. tendo, to stretch out,

extend) are the most common form of attachment

and serve to concentrate the pull of the muscle to

a small area on the bone. Tendons are very strong.

Their tensile strength has been estimated to be 4,169

pounds (1,891 kilograms) per square inch in an adult

FIGURE 2.5 Muscle fiber arrangement. (A) Fusiform, (B) penniform.

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