Relationship between scapular internal rotation and upper-trunk movements during right and left hand-behind-back movements

[Purpose] This study aimed to clarify the relationship between scapular internal rotation and upper-trunk movement during hand-behind-back movements of the right and left hands. [Participants and Methods] We included 20 healthy right-handed men and measured their hand-behind-back movements while sitting, using a three-dimensional motion capture system. We examined the relationship between scapular internal rotation and upper-trunk movements during hand-behind-back movements with the right and left hands. [Results] The right scapular internal rotation angle was negatively correlated with the anteroposterior tilt angle of the upper-trunk, and increased scapular internal rotation was associated with an increased posterior tilt of the upper-trunk. Moreover, the left scapular internal rotation angle was significantly correlated with the upper-trunk anteroposterior tilt angle and upper-trunk rotation angle, and increased scapular internal rotation correlated with increased anterior tilt of the upper-trunk and contralateral rotation. [Conclusion] Scapular internal rotation during hand-behind-back movements was associated with upper-trunk movement, with differences observed between the right and left hands. It is useful to evaluate and treat the movement of the upper-trunk and scapulothoracic joint on both sides to increase scapular internal rotation during hand-behind-back movements.