Association of the scapulothoracic kinematics and the musculotendinous architecture of supraspinatus during scaption in male college volleyball players with scapular dyskinesis.

Scapular dyskinesis (SD) is prevalent among overhead athletes and associated with dysfunctions of the rotator cuff. Although the musculotendinous architecture of the supraspinatus changes with arm elevation, the influence of scapular kinematics remains unclear. Thus, this study aimed to investigate the dynamic changes in the supraspinatus's musculotendinous architecture and its association with scapular kinematics during scaption in participants with SD. Twenty-one asymptomatic male college volleyball players with type I SD were recruited. Participants were asked to perform scaption from 0° to 60° while the pennation angle (PA) and fiber bundle length (FBL) of supraspinatus were measured using real-time sonography synchronized with a motion capture system to record scapular kinematics. Paired t-tests were used to compare the scapular kinematics, PA, and FBL between 0° and 60° of scaption. Multivariable regression analysis examined the relationship between the scapular kinematics and the FBL or PA. At 60° of scaption, participants demonstrated greater scapular upward rotation and posterior tilting (p < 0.001), along with shorter FBL and larger PA (p < 0.05), compared with 0°. Scapular kinematics significantly explained the variance in FBL, but not in PA. At 60°, scapular upward rotation was significantly associated with FBL lengthening (β = -0.56, p = 0.02). Scapular upward rotation facilitates lengthening of the supraspinatus during arm elevation. These findings suggest that impaired scapular control in SD may compromise rotator cuff performance. Rehabilitation for supraspinatus dysfunction should incorporate scapular motion training.