Kinematic and EMG characteristics of simple shoulder movements with proprioception and visual feedback.

The objective of this study was to determine if simple, shoulder movements use the dual control hypothesis strategy, previously demonstrated with elbow movements, and to see if this strategy also applies in the absence of visual feedback. Twenty subjects were seated with their right arm abducted to 90 degrees and externally rotated in the scapular plane. Subjects internally rotated to a target position using a custom shoulder wheel at three different speeds with and without visual feedback. Kinematics were collected with a motion analysis system and electromyographic (EMG) recordings of the pectoralis major (PECT), infraspinatus (INFRA), anterior and posterior (ADELT, PDELT) deltoid muscles were used to evaluate muscle activity patterns during movements. Kinematics changed as movement speed increased with less accuracy (p<0.01). Greater EMG activity was observed in the PECT, PDELT, and INFRA with shorter durations for the ADELT, PDELT and INFRA. Movements with only kinesthetic feedback were less accurate (p<0.01) and performed faster (p<0.01) than movements with visual feedback. EMG activity suggests no major difference in CNS control strategies in movements with and without visual feedback. Greater resolution with visual feedback enables the implementation of a dual control strategy, allowing greater movement velocity while maintaining accuracy.