Due to decreasing moment arm with abduction, supraspinatus
is a more effective shoulder abductor in scapular plane at lower
abduction angles in contrast to anterior
deltoid and lateral deltoid
which are more effective shoulder abductors at higher abduction
angles (Otis JC et al, 1994).
In scapular plane, supraspinatus generates greatest abduction
torque with shoulder in neutral rotation or only within slight
interal or external rotation. (Liu J et al 1997; Otis JC et al,
*Supraspinatus assists in external rotation when shoulder
is abducted and internal rotation when shoulder is flexed (Ackland
DC & Pandy MG, 2011).
Supraspinatus is most often injured rotator cuff muscle. The
inability to smoothly abduct arm against resistance may indicate
rotator cuff injury. See supraspinatus