Trapezius activity and intramuscular balance during isokinetic exercise in overhead athletes with impingement symptoms A. M. Cools 1 , G. A. Declercq 2 , D. C. Cambier 1 , N. N. Mahieu 1 , E. E. Witvrouw 1 1 Department of Rehabilitation Sciences and Physiotherapy, Faculty of Medicine and Health Sciences, University Hospital, Ghent, Belgium, 2 Dreef Van Zonnebos 13, 2970 ‘s Gravenwezel, Belgium Corresponding author: Ann M. Cools, Department of Rehabilitation Sciences and Physiotherapy, University Hospital Ghent, De Pintelaan 185, 6K3, B9000 Ghent, Belgium. Tel: 132/240 26 32, Fax: 132/240 38 11, E-mail: ann.cools@ugent.be Accepted for publication 4 May 2006 We compared normalized trapezius muscle activity and intramuscular balance ratios between overhead athletes with impingement symptoms and non-injured athletes during iso- kinetic abduction and external rotation movements. Thirty- nine overhead athletes with chronic impingement symptoms and 30 non-injured athletes participated in the study. Electro- myographic activity of upper, middle, and lower trapezius was measured during isokinetic abduction and external rotation, using surface electrodes. The results show a significant increase of upper trapezius activity during both movements in the patient group, with decreased activity in the lower trapezius during abduction, and in the middle trapezius during external rotation. Analysis of the intramuscular activity ratios revealed muscle imbalance on the injured side of the patient group for upper/middle trapezius and upper/lower trapezius during abduction, and for all three muscle activity ratios during external rotation. These results confirm the presence of scapular muscle imbalances in patients with impingement symptoms and emphasize the relevance of restoration of scapular muscle balance in shoulder rehabilitation. The scapula plays a vital role in normal upper extremity function. The quality of scapular function depends, among others, on scapular muscle perfor- mance. Through their actions, the scapular muscles must provide stability as well as controlled mobility to the scapula. Compared with other joints in the human body, this double task, performed by the same muscle group, is specific for the scapulo-thor- acic muscles, and puts them under considerable stress. These demands are aggravated by the fact that there are very less bony articulations between the scapula and the trunk. Particularly in overhead sports activities, the scapular muscles are subjected to extremely high loads in maintaining proper gle- nohumeral alignment and transferring lower extre- mity and trunk energy into the throwing arm (Kibler, 1998a, b; Burkhart et al., 2003). Because the scapula plays a critical role in control- ling the position of the glenoid, relatively small changes in the action of scapulo-thoracic muscles can affect the alignment and forces involved in movement around the glenohumeral joint. This may lead to tensile overload of the rotator cuff and impingement symptoms (Su et al., 2004; Karduna et al., 2005; Myers et al., 2005). Research indicates that shoulder impingement is the most common cause of shoulder pain in overhead athletes (Altchek et al., 1990; Tibone & Shaffer, 1995). The term shoulder impingement was first introduced by Neer (1972), who described the phe- nomenon as a mechanical compression of the rotator cuff and subacromial bursa against the anterior undersurface of the acromion and coracoacromial ligament, particularly during elevation of the arm. In more recent literature, impingement has been de- scribed as a group of symptoms rather than a specific diagnosis. In this current opinion, it is thought that numerous underlying pathologies may cause impin- gement symptoms. Glenohumeral instability (Kam- kar, 1993; Jobe, 1996; Kibler, 1998b; Meister, 2000), rotator cuff or biceps pathology (Jobe, 1996; Morri- son et al., 2000), scapular dyskinesis (Kamkar, 1993; Kibler, 1998a; Burkhart et al., 2003), and glenohum- eral internal rotation deficit (Warner et al., 1990; Burkhart et al., 2003; Michener et al., 2003) have been associated with impingement symptoms in the clinical literature. Different anatomical structures can be impinged internally or externally, probably depending on the motion and loading put on the shoulder during the pain-provoking activity (Cavallo & Speer, 1998; Sørensen & Jørgensen, 2000). How- ever, a possible instability in the shoulder is often ‘‘silent’’ and difficult to demonstrate by ordinary tests and has therefore been termed ‘‘functional Scand J Med Sci Sports 2007: 17: 25–33 COPYRIGHT & BLACKWELL MUNKSGAARD 2006 Printed in Singapore . All rights reserved DOI: 10.1111/j.1600-0838.2006.00570.x 25