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Shoulder complaints occur frequently in the general population, the lifetime prevalence ranges from 6.7 to 66.7%. (1) The most frequently occurring shoulder complaints are subacromial pain syndrome (SPS) and glenohumeral instability (GHI). Of all shoulder complaints 44-65% is diagnosed as SPS. (2)

The humerus is attached to the glenoid, through the joint capsule and the rotator cuff. These 2 structures form a functional entity. (3) The glenoid as a part of the scapula is not attached to the thorax through any passive structures. Therefore, the scapula depends greatly on muscle function for stability. Muscular stabilization of the scapula, relative to the thorax, is accomplished by the M. lower trapezius and M. serratus anterior (SA). (4) If muscular stability decreases the shoulder may be susceptible to injury. (5) Decreased stability of the scapula can be observed as an altered scapular movement or position, when comparing the left-to-right side. This asymmetry in movement or position is called scapular dyskinesis. (4)

Scapular dyskinesis has been found in patients with SPS as well as GHI. It is estimated that 64% of patients with GHI have scapular dyskinesis. (6) Even though the exact nature of the relationship between shoulder complaints and scapular dyskinesis is currently unclear, there is a general consensus that when scapular dyskinesis is diagnosed, it is necessary to quantify and treat it. (4,7,8)

Scapular dyskinesis can have several causes. First, decreased muscle function of the Lower Trapezius and/or Serratus Anterior, which will result in decreased activity or delayed muscle onset. Secondly, increased activity of the Upper Trapezius, and an altered scapula resting position can also contribute to scapular dyskinesis. In turn these changes in muscle activity can be brought about by several mechanisms such as fractures, rotator cuff ruptures, cervical complaints, GHI and SPS. (4,7,9)

Exercise therapy is often used as a treatment strategy within shoulder rehabilitation. Several studies have investigated the effectiveness of scapulothoracic exercise on shoulder function in patients with shoulder complaints, and found it to be effective (10–12) Scapulothoracic exercises are used frequently in the first phases of the rehabilitation. (13) These exercises can be performed under supervision of a physical therapist and/or at home. Regular exercise therapy, aimed at improving scapulothoracic muscle function, can be augmented using surface electromyography (sEMG). Using the sEMG augmentation, patients can perform their home exercise schedule with real-time sEMG. Possibly this could improve the patient satisfaction and therefore motivation to perform the exercises, the exercise technique, and adherence. Increases in all or any of these factors could improve treatment outcomes.

The sEMG augmentation of the home exercises uses an external focus of attention. By using this motor learning strategy, the emphasis is placed upon focusing on the result of a movement, rather than focusing on the body or shoulder, which is called an internal focus of attention. Providing an external focus of attention increases the efficiency of the motor learning process. (14) There are increasing amounts of evidence for the efficacy of an external focus of attention in motor learning, although mainly for lower extremity tasks. (15–17) For upper extremity tasks less studies have been performed. (18)

This study aims to investigate the effectiveness of adding real-time sEMG during home exercise performance to shoulder rehabilitation, and to compare this to regular shoulder rehabilitation in which real-time sEMG is only provided during treatment sessions and to shoulder rehabilitation without any form of real-time sEMG.

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