The anterior deltoid is involved in shoulder
abducted when the shoulder is externally
rotated. The anterior deltoid is weak in strict transverse
flexion but assists the pectoralis
major during shoulder transverse flexion / shoulder flexion
(elbow slightly inferior to shoulders).
Due to increasing moment arm with abduction, anterior deltoid
is more effective at shoulder abductor in higher abduction angles
in contrast to supraspinatus
which more effective shoulder abductor at lower abduction angles.