Dance Anatomy & Kinesiology

The Upper Extremity 389

deltoid, middle deltoid, and posterior deltoid. The

anterior deltoid traverses the front of the shoulder,

and its lateral and downward course produces a line

of pull allowing its primary actions of shoulder flexion

and horizontal adduction (figure 7.14). It can also

assist with abduction of the shoulder and probably

internal rotation. The middle deltoid courses later-

ally over the top of the shoulder and then downward

to attach onto the humerus, making it an important

and powerful abductor of the shoulder (figure 7.15).

Its activity increases progressively as the arm is

raised and is greatest between 90° and 180° of

shoulder abduction (Basmajian and DeLuca, 1985;

Hamill and Knutzen, 1995), and the arm cannot be

raised above shoulder height when this muscle is

missing. The posterior deltoid crosses the back of

the shoulder joint and can be thought of as having

opposite actions to the anterior deltoid (figure

7.16). The posterior deltoid is an important shoulder

extensor, and a loss of the ability to raise the arm

backward above waist height tends to accompany

loss of this muscle. The posterior deltoid also can

produce horizontal abduction, probably contributes slightly to shoulder external rotation, and helps

prevent downward dislocation of the humerus.

Surprisingly, there is one movement in which the anterior and posterior deltoid can actually work

together, and that is shoulder adduction. With shoulder adduction, their simultaneous synergistic

contraction allows shoulder adduction while neutralizing out undesired other actions of shoulder flex-

ion-extension, horizontal abduction-adduction, and external-internal rotation. In addition, the deltoid

appears to function to help stabilize the shoulder joint, and often two or three parts of the deltoid tend

to be active when the arm is moved, with greater activity in the portion of the muscle generating the

desired movement (Rasch, 1989).

Palpation: The deltoid can easily be seen and palpated at the front, top, and back of the shoulder.

Sit with the fingers of the left hand on the front of the right shoulder. You can feel the anterior deltoid

contracting when you raise your right arm to the front slowly from low fifth (shoulder flexion). You can

palpate the middle deltoid on the top of the shoulder just inferior to the tip of the acromion process

when raising the right arm from low fifth to second position (involves shoulder abduction). The poste-

rior deltoid can be felt contracting on the back of the shoulder when the right arm is raised backward

(shoulder hyperextension).

FIGURE 7.15 Lateral view of deltoid (right shoulder).

Attachments and Primary Actions of Coracobrachialis

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

Coracobrachialis

(kor-ah-ko-bra-kee-AL-is)

Coracoid process of

scapula

Anteromedial aspect of

middle of humerus

Shoulder flexion

Shoulder adduction

Shoulder horizontal adduction

Coracobrachialis

The coracobrachialis (coraco, coracoid + brachi, arm) is a small muscle located beneath the pectoralis

major and anterior deltoid on the anteromedial aspect of the shoulder and arm. Its name describes its

attachments, and it runs from the coracoid process of the scapula downward to attach to the antero-

medial aspect of the humerus. It is pictured later in this chapter with the brachialis (see figure 7.42 on

p. 417). The actions of the coracobrachialis include shoulder flexion and horizontal adduction, but due

to its small size, its contribution is less significant than that of the pectoralis major or anterior deltoid.

It can also work with other muscles to produce shoulder adduction.

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