The lateral deltoid is involved in shoulder
abduction when the shoulder is internally
rotated. It is involved in shoulder
flexion when the shoulder is internally rotated. It is involved
in shoulder
transverse abduction (shoulder externally
rotated) but is not utilized significantly during strict
transverse
extension (shoulder
internally rotated).
Due to increasing moment arm with abduction, lateral deltoid
is more effective at shoulder abductor in higher abduction angles
in contrast to supraspinatus
which more effective shoulder abductor at lower abduction angles.
