52 Dance Anatomy and Kinesiology
the torque produced by the resistance is greater
than the torque produced by the muscle, and the
direction of movement is opposite to that of the
muscle torque and in the same direction as that of
the resistance.
In human movement, this type of contraction is
commonly used to control the effects of gravity, to
decelerate body segments, and to help absorb shock
loads (Dye and Vaupel, 2000). For example, in the
down-phase of the biceps curl (table 2.3C), gravity is
the external force that is producing the movement,
and the elbow flexors are working eccentrically to
help control the movement. If the elbow flexors were
not used, gravity would make the weight drop very
rapidly, potentially causing joint injury. In this case
the resistance torque is greater than that of the mus-
cles. It is important to notice that even though elbow
extension is occurring (due to the effects of gravity),
it is the elbow flexors and not the elbow extensors
that are being used to control this extension. So, the
same muscle group is working on the up-phase as on
the down-phase, only with a concentric and eccentric
contraction, respectively. Eccentric contractions arecommonly used on the down-phase of movements
in dance, such as the descent of a plié, landing from
a jump, or lowering the arms from overhead to the
sides of the body.Static (Isometric) Muscle Contraction
A static or isometric contraction (G. iso, same +
metron, measure) loosely means “equal length” and
involves a partial or complete contraction of a muscle
where no visible joint movement occurs. On a sar-
comere level, there is a small initial pulling of the
actin toward the center of the sarcomere until the
slack is taken out of the muscle-tendon complex as
a whole, and then cross-bridge formation cyclically
occurs at the same sites. So, although there is active
tension being generated by the involved muscle,
the torque generated by the muscle is being exactly
counterbalanced by that of the resistance such that
no net movement occurs. The resistance can be from
internal forces generated from contracting muscles
with oppposite actions or the result of an external
force such as another person, a weight, or gravity.“Pull Up Your Knees”
W
hile some schools prefer a more relaxed stance, other schools of dance encourage students to
“pull up the knees” on the support leg when working at the barre or center floor. This cue is
often further elaborated by encouraging students to not let the thigh muscles be “relaxed,” the knee-
caps be “loose,” or the support knee bend or “wobble.” From an anatomical perspective, tightening
the quadriceps femoris muscle can pull the patella upward, add the desired tension to the thigh, offer
joint stability (large parallel stabilizing component), and prevent the knee from bending. Although
a maximum contraction of the quadriceps is not recommended due to the aesthetic in many dance
forms to avoid overdevelopment of the thighs and from a perspective of desired movement efficiency,
a slight contraction of the quadriceps can help stabilize the support knee and prepare the muscles for
necessary rapid slight adjustments as the gesture leg is moving. Tensing muscles around a joint can
enhance some of the muscle receptors’ sensitivity to stretch and markedly enhance proprioception at
that joint (Irrgang and Neri, 2000). It can also help counter the tendency that some dancers have of
relying too much on passive constraints such as the ligaments for stability.
Some dancers, however, tend to create a hyperextended position of the knee when they contract the
quadriceps. In these cases, cueing to “lightly pull the kneecap up versus back,” or cueing to “gently pull
up both the front and back of your knees” may be helpful. In the latter case the desire is to generate a
slight co-contraction of the quadriceps and hamstrings that can create a balanced stability and readiness
with the hamstrings (knee flexors) acting to prevent potential knee hyperextension that is sometimes
associated with excessive contraction of the quadriceps femoris. Some examples of electromyography
recordings from the quadriceps femoris, hamstrings, and adductors from selected dancers are shown
later in the chapter to demonstrate the individual differences in muscle activation associated with
standing “in preparation” in turned-out first position (see Tests and Measurements 2.1 on p. 64).