34 Dance Anatomy and Kinesiology
I
n this chapter we examine the muscular system. It
is the muscular system that produces movements
of the skeletal system. We could not walk or dance
without the motive force provided by our muscles.
Muscles have a unique ability to produce tension that
is translated to bones to produce joint movement.
In addition, muscles can offer constraints to motion
when the limits of their extensibility are approached.
Hence, adequate flexibility, as well as strength, is
essential for the expansive movements encompassed
in dance. The large leap (grand jeté en avant) shown
in the photo on page 33 exemplifies these demands
for both muscular strength and flexibility to project
the body through space and achieve the desired lines
of the body segments. Learning about how muscles
work is key for understanding and describing human
movement. Topics covered in this chapter include
the following:- Skeletal muscle structure and function
- Microstructure of skeletal muscle and muscle
contraction - Muscle architecture
- Muscle attachments to bone
- Muscles, levers, and rotary motion
- Types of muscle contraction (tension)
- Muscular considerations in whole body movement
- Learning muscle names and actions
Skeletal Muscle Structure and Function
Muscle cells are the only cells capable of producing
active tension and contracting. Contractility is the
unique ability of muscle tissue to shorten. Some
recent texts substitute “the ability to produce ten-
sion” for “contractility,” since tension produced by
muscles does not always result in a shortening of
muscles (see Types of Muscle Contraction [Tension]
on p. 50 for more information). It is this property of
contractility that generates movement of the human
body, as well as allows for movements in the heart
and other internal organs. There are three types of
muscle tissue—smooth muscle, cardiac muscle, and
skeletal muscle—shown in table 2.1. Smooth muscle
forms part of the walls of hollow organs (e.g., blad-
der, uterus, stomach) and various systems of tubes
(e.g., within the circulatory, digestive, respiratory,
and reproductive systems). Contraction of smooth
muscles helps move substances through organs
(such as food through the stomach) and through
tubes (such as blood through arteries). Under alight microscope, smooth muscle cells appear long,
narrow, and spindle shaped, with a single central
nucleus. The cells are very closely aligned to form
sheets, and as their name suggests, lacking in cross-
striations. Smooth muscle contraction is not under
voluntary control; hence this type of muscle is termed
involuntary muscle. It also has the ability to maintain
tone and contract automatically, without stimulation
from the nervous system.
Cardiac muscle is the type of muscle found in the
walls of the heart. The contraction of cardiac muscle
helps pump blood via blood vessels to the lungs and
other parts of the body. Under the light microscope,
cardiac muscle fibers have bands, termed striations,
that run across the width of the cell. Cardiac muscle
fibers are also short and branched with unique junc-
tions, termed intercalated discs, at the abutment
of the ends of adjacent cells. Cardiac muscle cells
generally contain a single nucleus (uninucleate)
but sometimes two (binucleate). Similar to smooth
muscle, cardiac muscle is not under voluntary
control (involuntary), and due to specialized cells
(pacemaker cells) is able to contract automatically,
without stimulation from the nervous system.
Skeletal muscle is the type of muscle that attaches
to the bones of the skeleton and gives rise to move-
ments at joints. Although influenced by gender, body
type, and activity, these muscles make up approxi-
mately 40% to 45% of an average adult’s body weight
(Hall, 1999). Under the light microscope, a skeletal
muscle cell is very long, narrow, and cylindrical, with
many cross-striations and many nuclei (multinucle-
ate). Unlike smooth and cardiac muscles, which
generally work with little conscious control, skeletal
muscles are called voluntary because many can be
controlled at will. Unlike smooth and cardiac mus-
cles, they cannot contract automatically and instead
rely on stimulation from a nerve. Skeletal muscles
are also important for the maintenance of posture
and positions, stability of joints, shock absorption,
support and protection of internal tissues, control of
pressures within cavities, and production of body heat.
Greater than 75% of the energy utilized with muscle
contraction is released as heat (McGinnis, 2005).
Because of its importance for human movement, this
book focuses on skeletal muscle, and any further refer-
ence to muscle will be to skeletal muscle only.Properties of Skeletal Muscle Tissue
In addition to contractility, skeletal muscle is char-
acterized by the following properties: irritability,
extensibility, and elasticity. Irritability is the ability to
receive and respond to a stimulus, commonly from