The antagonist fires in an eccentric contraction to slow the movement and change direction. When you abduct your shoulders with webbed gloves, your medial deltoids contract concentrically.

What kind of contraction is shoulder abduction?

Isometric Contraction of Scapular Muscles Activities during Horizontal Abduction and Adduction of the Shoulder.

Which muscle eccentrically controls adduction of the shoulder?

Adduction is accomplished primarily by the pectoralis major, latissimus dorsi, teres major, triceps, and coracobrachialis. The deltoid and the supraspinatus, a muscle that runs along the scapula in the back, are the two main abductors of the shoulder.