The scapular movement could not be monitored directly with the currently available video-based method because the scapular moves widely under subcutaneous tissues. In the present study, a convenient, video-based method was developed to estimate the scapular rotation indirectly for given humeral rotation measured in dynamic activities. Four male university students with no shoulder injury participated in the present study. Each subject was asked to hold the right arm at each of the 25 selected positions. While the subject was holding the position, reflective markers were attached on the skin above the selected scapular anatomical landmark and the three-dimensional coordinates of the markers were measured with optical motion capture system. The orientations of the scapula and humerus relative to thorax were expressed as Euler angles. The scapular rotations were expressed as a function of humeral rotations. The derived functions were then used to estimate the scapular rotations for given set of humeral rotations during humeral elevation. The validity of the present methodology was tested with the use of electromagnetic sensor. The present method well predicts scapular internal rotation for horizontal adduction greater than 30° and scapular upward rotation during humeral elevation. The scapular posterior tilt was not estimated accurately.
