68 Dance Anatomy and Kinesiology
toward the trunk to increase hip flexion and stretch
intensity. In the advanced standing hamstring stretch
shown in figure 2.23C (performed with the foot of
the upper leg resting on a wall), gravity will intensify
the stretch (hip flexion) when the trunk is leaned
forward. However, as flexibility progresses and the
dancer gets closer to the wall, gravity plays less of a
role and the arms are classically used to pull the torso
further forward.
When one is considering appropriate exercises
for injury prevention and treatment, it is essential to
understand the underlying mechanics or principles
that are associated with a given injury. For example,
as will be discussed in chapter 5, improper movement
(tracking) of the patella is believed to underscore
some injuries involving the kneecap. The quadriceps
femoris muscle, and specifically the vastus medialis, is
vital for correct movement of the patella, and hence
specific strengthening of the quadriceps femoris is
one recommendation for prevention of such prob-
lems. The addition of the sections on injuries to
chapters 3 through 7 is not to suggest that readers
who are not medical professionals diagnose and treat
their own injuries or those of their students/associ-
ates. Diagnosis and treatment of injuries should be
performed only by qualified medical professionals.
Rather, the intent of these sections is to elucidate
some of the theorized relationships between injuries
and the anatomy and mechanics discussed in the
given chapter so that dancers can be more effective in
preventing injuries and have a better understanding
of why certain exercises might be recommended in
medically prescribed rehabilitation programs.Summary
Skeletal muscle gives rise to movements at joints.
Skeletal muscle contains both elastic and contractilecomponents. The elastic components play an impor-
tant role in stretching muscle and in the passive
contribution to muscle force. The contractile com-
ponents are the active elements of muscle. According
to the sliding-filament theory, a coupling of small
filaments within the muscle produces muscle tension
or contraction. The skeletal muscles are attached
to bones via tendons or aponeurosis, and so muscle
contraction can be translated into rotary motions at
joints. Depending on the balance of torque related
to muscle effort and torque related to resistance at
a given joint, muscle contractions can be dynamic
(concentric or eccentric) or static (isometric). These
different types of muscle contractions help muscles
serve their varied roles as prime movers, antagonists,
synergists, and stabilizers.
Individual muscles vary in their relative per-
centage of slow-twitch and fast-twitch fibers, cross-
sectional area, and fusiform or penniform fiber
arrangement in accordance with functional demands
for greater force production, greater speed/range of
motion, or greater postural control. When learning
individual muscles it is helpful to take into account
the meaning of Latin or Greek word roots utilized in
their names and locations. The location of the proxi-
mal and distal attachments of a muscle creates a “line
of pull,” and from the relationship of this line to the
axis of the joint one can deduce the possible actions
of a muscle. Knowledge of the actions of muscles can
also be used to analyze movements and predict the
muscles that would function as prime movers in a
given movement. To be accurate, such an analysis must
take into account the role of gravity and the types of
muscle contractions occurring in different phases of
the movement. Knowledge of muscle actions can also
be used to design effective strength exercises and
flexibility exercises, and to better understand why
certain exercises would be valuable for prevention
and treatment of common dance injuries.