Dance Anatomy & Kinesiology

400 Dance Anatomy and Kinesiology

rotation of the humerus allows the greater tubercle

of the humerus to pass behind the coracoacromial

arch (Caillet, 1996; Magee, 1997), which permits an

additional 30° of abduction of the humerus (Hamill

and Knutzen, 1995). It is interesting to note the par-

allel situation at the hip, where external rotation of

the femur and bringing the greater trochanter closer

to the ischial tuberosities (sitz bones) allows much

greater hip abduction range than when the femur is

maintained in a parallel or internally rotated posi-

tion. As with the hip, adequate strength and appro-

priate activation of the external rotators (particularly

the infraspinatus and teres minor of the rotator cuff)

are key for correct mechanics.

SIT Force Couple

When the arm is relaxed and hanging by the side,

the head of the humerus tends to sit in the upper

part of the glenoid cavity (Magee, 1997), and with

contraction of the middle deltoid a large compo-

nent of the muscle force will tend to pull the head

Influence of External Forces on Scapular Stabilization

Use the following exercise with a partner to demonstrate the influence of pushing and pulling on the

muscles used to stabilize the scapula.

• Pushing. Face a partner with right palms in contact and arms at shoulder height with the elbows
  extended. Push against your partner, and note that if you relax the scapular muscles, the right scapula
  will tend to be pushed backward (scapular adduction). Now focus on keeping the scapula stationary
  as you push, and notice the serratus anterior, located near your armpit on the front of your chest,
  contracting to help stabilize the scapula with its function of scapular abduction.


• Pulling. Now face your partner with right hands grasped as if to shake hands. The next step is
  for both of you to slowly pull on each other’s hand. Notice that if you relax the scapular muscles the
  right scapula will tend to be pulled forward (scapular abduction). Now focus on keeping the scapula
  stationary as you pull, and notice the contraction of the trapezius and other muscles between the
  shoulder blades to produce scapular adduction and prevent forward movement of the scapula.

CONCEPT DEMONSTRATION 7.2

Influence of External Rotation

on Overhead Arm Movements

Working with a partner, raise his or her left arm in abduction, as if to bring it overhead through second

position to a high fifth position as directed in the following.

• Internal rotation. First, perform this motion slowly and gently while holding the arm in internal
  rotation. Note how the scapula elevates excessively, the shoulder “hikes,” and it is difficult to bring
  the arm fully overhead.


• External rotation. Now, from this elevated position, slowly externally rotate the arm, and note
  how the scapula and shoulder “drop” and the arm can be easily brought overhead. Now slowly raise
  your partner’s arm to the side from a low to high position, adding a gradual external rotation as the
  arm is raised, and note how this allows the desired dance aesthetic of keeping the shoulders down
  while bringing the arm overhead.

CONCEPT DEMONSTRATION 7.3