The goal of this project will be to develop biomechanical guidelines for optimum, non-stressful shoulder function. Specifically the aims to define the timing, relative intensity and synergies of shoulder muscle action and the shoulder joint motion and forces involved in wheelchair propulsion and body transfer by SCI patients with discriminating levels of complete paraplegia and quadriplegia. Today's increased longevity and mobility of spinal cord injury (SCI) patients has led to disabling shoulder pain becoming a significant clinical problem which appears to be a consequence of overuse. To assess the underlying pathomechanics responsible for the shoulder joint pain, asymptomatic shoulder muscle function and joint mechanics during the primary high demand activities of SCI patients must be documented. Four functional groups of asymptomatic complete SCI patients (lumbar and thoracic paraplegics, low and C6 quadriplegics) and one group of SCI patients with painful shoulders will be tested. Function of the supraspinatus, infraspinatus, subscapularis, anterior, middle, and posterior deltoid, long head of biceps brachii, serratus anterior, latissimus dorsi and pectoralis major will be recorded with dynamic EMG using intramuscular fine wire electrodes and telemetered signal transmission. Motion of the shoulder, elbow and wrist joints will be measured with the Vicon Motion Analysis System. Wheelchair propulsion forces will be recorded with a strain gauge instrumented wheel. With a modified bicycle ergometer the resistance of several locomotor conditions will simulated. These data will be collected simultaneously while the subjects perform body transfers and wheel their chairs at free and fast velocities on a vinyl tile and carpeted floor, on the ergometer set to reproduce the resistance of inclines (2 and 4 degrees) and rough surfaces (carpet and concrete) and around an outdoor concrete track for a 22 minute endurance test. Prior to the functional tests, maximal isometric shoulder elevation in the scapular plane (scaption) and internal and external rotation torques will be measured with a Cybex dynamometer. Shoulder depressor and trunk flexion and extension forces will be recorded with a cable tensiometer. The data will be analyzed to correlate patterns of muscle activity with the joint motions and propulsion forces. Shoulder joint moments and forces will be calculated. The influence of trunk stability and fatigue on shoulder muscle function will be assessed. The relative demands of the different environmental situations will be determined. Statistical significance of the findings will be determined by split-plot ANOVA and regression analyses.
