The Effects of Muscle Characteristics on the Control of Shoulder Complex During Functional Movements

The movement control of shoulder joint relies not only on the glenohumeral joint, but also the critical contributions from scapulothoracic joint. The relating scapula muscle strength, scapula mobility and, the most important of all, the capacity of neuromuscular control should be integrated into the rehabilitation program for patients with shoulder disorders. With regarding to the subacromial impingement syndrome or rotator tendinopathy, the status of scapula dyskinesia and dysfunctions were improved significantly after the intervention of scapula-emphasized exercise. But there was no study addressed the relationships between stiffness of relating muscles and the deficits of scapula movement. The stiffness had been shown to serve an important role in functional performance of the corresponding joint. For example, the decreased elasticity of supraspinatus muscle was noticed on affected side comparing in patients with impingement syndrome.Few studies examined the effects of altered muscle stiffness on kinematic performance in shoulder complex. Laudner et al. found that the stiffer the latismuss dorsi muscle was, the less upward rotation and posterior tilting, and the more internal rotation of scapula during arm elevation was exhibited in asymptomatic swimmers. Another study showed that the increased range of external rotation and posterior tilt of scapula during arm elevation were associated with the decreased stiffness of pectoralis minor. The recent study presented that the electromyographic activities and elasticities of middle deltoid, supraspinatus, and infraspinatus muscles correlated significantly with the tissue elasticity during shoulder movement in healthy shoulder. However, there was no scientific information directly to prove the changes in characteristics of rotator cuff function as well as the impacts on kinematic control of shoulder complex. Therefore, the aim of this study is to examine the relationship among characteristics of muscle properties and ki