Dance Anatomy & Kinesiology

388 Dance Anatomy and Kinesiology

pushing, throwing, and punching movements (Hamilton and Luttgens, 2002). When the pectoralis major

is missing, the arm can still be raised and lowered, but the power in shoulder flexion and extension is

markedly diminished (Rasch and Burke, 1978).

Palpation: Use your left hand to pinch the fold of muscle that forms the front of the right armpit (axilla)

while your right hand is placed on a stationary object such as a desk. You can feel the sternal head

of the pectoralis major contracting under your fingers when you firmly press your right hand down onto

the desk as if to extend the shoulder (isometric shoulder extension). To palpate the clavicular portion,

move the fingers of your left hand just below the middle of the clavicle and your right hand under the

desk. You can palpate the clavicular portion of the pectoralis major contracting when you firmly press

your right hand upward against the desktop (isometric shoulder flexion).

Attachments and Primary Actions of Deltoid

Muscle Proximal attachment(s) Distal attachment(s) Primary action(s)

Deltoid

(DEL-toid)

Outer anterior aspect of

clavicle

Acromion of scapula

Lower border of spine of

scapula

Deltoid tuberosity of

humerus

Anterior:

Shoulder flexion

Shoulder horizontal adduction

Assists with shoulder internal rotation

Middle:

Shoulder abduction

Shoulder horizontal abduction

Posterior:

Shoulder extension

Shoulder horizontal abduction

Assists with shoulder external rotation

Different Actions of Pectoralis Major

The differing functions of the clavicular and sternal portions of the pectoralis major can be demon-

strated with the following exercise.

• Shoulder flexion and extension. Sit with your hands clasped at shoulder height with both elbows
  extended. Pull down with the right arm (shoulder extension) and up (shoulder flexion) with the left arm
  simultaneously, such that no net movement of the shoulders occurs. Note the lower sternal portion
  of the pectoralis major contracting on the right side of your chest and the upper clavicular portion of
  the pectoralis major contracting on the left side of your chest.


• Shoulder horizontal adduction. Press both hands and arms toward each other so that no net
  movement of the shoulder occurs (isometric horizontal adduction). Note the clavicular and sternal
  portions of the pectoralis major contracting on both the right and left sides of your chest.

CONCEPT DEMONSTRATION 7.1

Deltoid Muscle

The deltoid (delta, triangular) muscle is the superficial muscle that forms the round contour of the

shoulder. As its name implies, it is triangular in shape (figure 7.15). The deltoid courses from the outer

clavicle and acromion process and spine of the scapula downward and outward to attach onto the deltoid

tuberosity located about halfway down on the lateral humerus. With its extensive proximal attachments,

it crosses the joint in many ways and is best thought of functionally as three muscles—the anterior