Table 1 Descriptions of the surface electrodes placement and MVIC normalization positions for each of the seven shoulder muscles examined

Middle deltoid

Intersection of the midpoint between the anterior and posterior deltoid muscles and the midpoint between the acromion and deltoid tuberosity

Resisted abduction at 0° elevation in scapular plane and elbow flexion to 90°

Anterior deltoid

3.5 cm below the anterior angle of the acromion

Resisted forward flexion at 0° elevation in scapular plane and elbow flexion to 90°

Supraspinatus

Midpoint and 2 finger-breadths

anterior to scapular spine

Resisted elevation at 90° elevation in scapular plane, 45° internal rotation and elbow extension

Upper trapezius

Supero-medial and infero-lateral to a point 2 cm lateral to one-half the distance between the C7 spinous process and the lateral tip of the acromion

Resisted shoulder shrug with subject seated and arm at side

Posterior deltoid

2 cm below the posterior angle of the acromion

Resisted extension at 0° elevation in scapular plane and elbow flexion to 90°

Infraspinatus

Parallel to spine of scapulae, approximately 4 cm below, over the infrascapular fossa

Resisted external rotation at 90° elevation in scapular plane and neutral rotation

Pectoralis major

3.5 cm medial to the anterior axillary line

Resisted horizontal adduction at 90° elevation in scapular plane and elbow flexion to 90°