The Movements Of The

The movements of the arms at the shoulder joint are more complii ed than the movements of the thigh at the hip joint because the ran of possible movements is greater, and also because the separation o he shoulders by the width of the rib cage allows the arms to be p ed across the chest in a manner that has no counterpart in the 1< "eT extremities.

In their simplest form flexion and extension of the arms are movem 'its in a sagittal (front-to-back; plane of the body, abduction and adductior ire movements of the arms in a frontal (side-to-side) plane of the body, nd medial and lateral rotation of the arms are movements of axial rota! in-

These can all be superimposed onto one another: you can flex, adduct, and rotate the arm all at the same time. And because the scapulae are also involved, the movements can best be understood by checking out the accompanying shills of the scapulae on a partner.

flexion and extension

First considering flexion, if you start from the anatomical position (fig 4.2) with the hands alongside the thighs and then lift your arms up and forward until they are straight out in front of you, you will be flexing them 90° (fig. 8.16), and you can continue this movement (flexion) up through an arc of 180" overhead, stopping anywhere along the way. Next considering extension, if you pull the arms straight to the rear from the anatomical position, you will be extending them. This movement does not occur in isolation, however; it also requires adduction of the scapulae (pulling them toward one another medially). Most people can extend their arms in a sagittal plane about 45° to the rear from a neutral position alongside the chest (fig. 8.15; figure also shows adduction superimposed on extension).

abduction and adduction

For abduction, first envision a frontal plane running through the ears, shoulders, chest, and lower extremities. Moving the arms from the anatomical position within such a plane, they will have been abducted 90° if you lift them straight out to the sides (fig. 8.17). Then if you continue to lift them until they are straight overhead, they will have been abducted 180°, in the same final position, incidentally, as when they are in i8or of flexion. The 180° of abduction and/or flexion, strictly speaking, always includes 6o° of upward rotation of the scapula, which we considered earlier.

Depending on your starting position, adduction is more complicated than flexion or extension. In the simplest situation, if you start with the arms straight out to the sides and then drop them down to a neutral position alongside the chest, you will be adducting them 90°. And if you start from 180° overhead, as in the final position for the tree (chapter 4), adduction will first swing the arms away from overhead to the spread-eagled 90° position (straight out to the sides) before coming back to the fully adducted position alongside the chest.

Adduction can also be superimposed on other movements. You can start with the arms flexed forward 90° (straight out in front) and then adduct them across the chest past one another, bringing the elbows together (fig. K-18). You can also start with the arms abducted 90' and then adduct them, not only straight back down into the anatomical position, just described, hut toward one another behind your back, at least minimally (fig. 8.19).

Figure 8.16. Arms flexed

Figure 8.17. Arms abducted 90°.

S. IIIH HhAnSTAKD 469

Adduction of the arms to the front from a flexed position also rounds the shoulders, which includes abduction of the scapulae (fig. 8.18); adduction of the arms to the rear from an abducted (fig. 8.iy) or extended (fig. 8.15) position includes pulling the shoulders to the rear, which in turn includes adduction of the scapulae.

circumduction

You can combine flexion and extension of the arm with abduction and adduction to yield the sequential movement called circumduction (see chapter 6 for circumduction of the thigh). For circumduction of the arm, flex it forward 90° while adducting it toward the midline, lift it overhead 180°, pull it around to the rear in an extended and adducted position, and then return it to a neutral position alongside the chest. Feel how circumduction of the arm affects the scapula: in the above sequence, circumduction of the arm first abducts the scapula as a result of flexing the arm forward and pulling it across the chest, then it elevates the scapula by lifting the arm overhead, adducts the scapula by pulling the arm to the rear, and depresses the scapula by bringing the arm back alongside the chest.

Figure 8.18. Arms flexed 90°, 'hen adducted.

Figure 8.19. Arms first abducted 90° (as in fig. 8.17), then adducted by pulling to the rear.

Figure 8.19. Arms first abducted 90° (as in fig. 8.17), then adducted by pulling to the rear.

470 ANATOM) OF HATHA Y<XiA MEDIAL AND LATERAL HOTATION

Medial and lateral rotation of the arms in the shoulder joint is comparable to medial and lateral rotation of the thighs; they are movements of axia rotation around an imaginary line through the center of the humerus. I you stand in the anatomical position with the elbows extended and rotat the arms so that the palms face to the sides as much as possible, you wi be rotating the arms laterally about 30°. Medial rotation of 6oc is ah possible but harder to isolate because it is easily confused with pronatii of the forearms.

Medial and lateral rotation of the arms can be carried out in ar position in combination with flexion, extension, abduction, or adductio For example, let's say you abduct the arms yo° straight out to the ski Next, to avoid confusing arm rotation with supination and pronation of tl forearms, flex the elbows yo°, pointing your hands straight to the froi Now swing the hands down through an arc of 30°: this motion has ju medially rotated the arms that amount. Or, swing the hands up, with t fingers pointed toward the ceiling (the "get your hands up" gesture in 1 grade B Western). This motion has just laterally rotated the arms 9 Notice that the scapulae participate extensively in all of these movemei

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