Brindle T, Uhl T, Nitz A, Shapiro R; Biodynamics Laboratory, University of Kentucky, Lexington, KY. Tbrindle@cc.nih.gov.

PURPOSE: This study examined the multidimensional nature of proprioceptive acuity and central nervous system (CNS) control of shoulder movements with either dominant visual or proprioceptive feedback, to identify if the CNS controls shoulder and elbow movements similarly. BACKGROUND: Studies of shoulder joint repositioning, have primarily evaluated only the afferent nature of proprioception incorporating extremely slow movement velocities. Moreover, these shoulder kinesthetic studies tend to measure only constant error (CE) with respect to the target position, but may overlook variable error (VE) with respect to performance. Studies of CNS control of simple elbow movements indicate modulation of amplitude of kinematic and electromyographic (EMG) parameters for fast movements and modulation of temporal parameters for slower movements. SUBJECTS: Twenty right side dominant subjects (10 males, 10 females) between the ages of 18 to 35 were recruited and screened to ensure no history of shoulder pathology was present. METHODS: With subjects seated and arm in the "plane of the scapula" and externally rotated 75^o, they internally rotated their shoulder to a target angle (27^o) with predominant visual or proprioceptive feedback at three different movement speeds. Movement speed was controlled via verbal instructions. High-speed motion analysis and EMG recorded temporal and amplitude parameters of kinematic and muscle activity patterns during movements. Normalized, kinematic phases were used to compare the three movement speeds. RESULTS: Significant increases (p<0.01) in CE (4.1^o +/-0.8^o) and VE (3.2^o +/- 0.2^o) were observed in the absence of vision, with VE similar to CE. Kinematic and EMG changes indicate similar, temporal control patterns for movements with visual and proprioceptive feedback. Speed of movement had greatest impact on kinematic and EMG patterns, specifically amplitude of muscle activity and magnitude of kinematic parameters. CONCLUSION: Reporting both CE and VE provide a more complete description of proprioceptive acuity. Kinematic and EMG are temporally modulated for proprioceptive movements, while it was the amplitude of kinematic and EMG patterns that were modulated as movement speed increased. CNS control of shoulder movements is consistent with CNS control of elbow movements and suggests a global strategy of amplitude control to increase movement speed. FUNDING SOURCE: Kentucky Physical Therapy Association.

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