Rehabilitation of Scapular Muscle Balance Which Exercises to Prescribe?

Ann M. Cools,*† PT, PhD, Vincent Dewitte,† PT, Frederick Lanszweert,† PT, Dries Notebaert,† PT, Arne Roets,‡ MPSS, Barbara Soetens,‡ PhD, Barbara Cagnie,† PT, PhD, and Erik E. Witvrouw,† PT, PhD

From: American Journal of Sport Medicine.
From the †Department of Rehabilitation Sciences and Physiotherapy, Faculty of Medicine and Health Sciences, University Hospital, Ghent, Belgium, and the ‡Department of Developmental, Personality and Social Psychology, Faculty of Psychology and Educational Sciences, Ghent University, Ghent, Belgium

Background: Strengthening exercises for the scapular muscles are used in the treatment of scapulothoracic dysfunction related to shoulder injury. In view of the intermuscular and intramuscular imbalances often established in these patients, exercises promoting lower trapezius (LT), middle trapezius (MT), and serratus anterior (SA) activation with minimal activity in the upper trapezius (UT) are recommended.

Hypothesis: Of 12 commonly used trapezius strengthening exercises, a selection can be performed for muscle balance rehabilitation, based on a low UT/LT, UT/MT, or UT/SA muscle ratio.

Study Design: Controlled laboratory study.
Methods: Electromyographic activity of the 3 trapezius parts and the SA was measured in 45 healthy subjects performing 12 commonly described scapular exercises, using surface electromyography.

Results: For each intramuscular trapezius ratio (UT/LT, UT/MT), 3 exercises were selected for restoration of muscle balance. The exercises side-lying external rotation, side-lying forward flexion, prone horizontal abduction with external rotation, and prone extension were found to be the most appropriate for intramuscular trapezius muscle balance rehabilitation. For the UT/SA ratio, none of the exercises met the criteria for optimal intermuscular balance restoration.

Conclusion: In cases of trapezius muscle imbalance, some exercises are preferable over others because of their low UT/LT and UT/MT ratios.

Clinical Relevance: In the selection of rehabilitation exercises, the clinician should have a preference for exercises with high ctivation of the LT and MT and low activity of the UT.

Keywords: shoulder rehabilitation; scapula; exercise; muscle balance; electromyography

INTRODUCTION

Shoulder pain and dysfunction are common complaints among individuals seeking care from physical medicine and rehabilitation specialists.1,46 Recently, clinicians25-27,36,42 and investigators11,29,31,33 have focused increased attentionon the role of the scapula in the pathogenesis of shoulder pain in general and impingement symptoms in particular. Scapulothoracic dysfunction, defined as alterations in the resting position or dynamic motion of the scapula, and changes in scapular muscle recruitment can affect many aspects of normal shoulder function.24 An increasing number of studies have correlated abnormalities in scapular position and motion (dyskinesis) with impingement symptoms, rotator cuff dysfunction, and instability.18,29,31,34,48. Various authors have suggested that shoulder abnormalities and abnormal scapular motions may be linked to global weakness of the scapulothoracic muscles8,9,15,16,38,43; others attribute scapular dyskinesis to scapular muscular imbalance rather than absolute strength deficits.8-10,29,40 In particular, excess activation of the upper trapezius (UT), combined with decreased control of the lower trapezius (LT) and the serratus anterior (SA), has been proposed as contributing to abnormal scapular motion.8-11,29,31,37,47 In view of the new insights and research findings on the role of the scapula in shoulder pathologic abnormality, current exercise protocols emphasize the importance of scapular muscle training as an essential component of shoulder rehabilitation.3,5,12,20,22,28,35,42,49 Restoration of muscle control and balanced coactivation in particular is a challenge to the clinician. For patients with an imbalance in the scapular muscles, selective activation of the weaker muscle parts with minimal activity in the hyperactive muscles is an important component in the reduction of the imbalance. Because a lack of activity in the LT, middle trapezius (MT), and SA frequently is combined with excessive use of the UT, the balance ratios UT/LT, UT/MT, and UT/SA are of particular importance.10,11,29,47 In addition, integration of shoulder girdle exercises into a global functional kinetic chain pattern has become a treatment goal in shoulder rehabilitation, specifically in overhead athletes.5,14,25 The selection of appropriate exercises in the rehabilitation of scapular muscle performance depends on the actual strength of the muscles but also on the relative strength of 1 muscle in relation to another. In a study by Ludewig et al,30 a selection of exercises was introduced with a low UT/SA ratio, meaning high activity in the SA with simultaneous minimal activation of the UT. However, no other exercises have been described to optimize the muscle balance within the trapezius muscle by calculating UT/LT and UT/MT muscle ratios. In addition, UT/SA ratios have not been calculated for exercises other than push-up exercises. Therefore, the purpose of this study was to determine the UT/LT, UT/MT, and UT/SA muscle ratios for a number of commonly used shoulder girdle strengthening exercises to determine which exercises are appropriate to optimize scapular muscle balance.

MATERIALS AND METHODS

Subjects Forty-five healthy volunteers (20 men, 25 women), recruited from the student population, participated in the study. Their mean age was 20.7 years (}1.7 years), mean height was 1.73 m (}0.09 m), mean weight was 65.15 kg (}10.89 kg), and mean body mass index was 21.75 (}2.39). Exclusion criteria for participation in the study were a history of cervical spine and shoulder injury or surgery, participation in overhead sports at a competitive level, and upper limb strength training for more than 5 hours per week. Inclusion and exclusion criteria were assessed with a questionnaire. Before participation, subjects read and signed the informed consent form. The investigation was approved by the Ethical Committee of Ghent University. Instrumentation Before electrode application, the skin was shaved if necessary and prepared with alcohol to reduce skin impedance (typically, <10 kÙ). Bipolar surface electrodes (Blue Sensor, Medicotest, Ballerup, Denmark) were placed with a 2-cm interelectrode distance over the upper, middle, and lower portions of the trapezius muscle and the lower portions of the SA muscle. Electrodes for the UT were placed midway between the spinous process of the seventh cervical vertebra and the posterior tip of the acromion process along the line of the trapezius. The MT electrode was placed midway on a horizontal line between the root of the spine of the scapula and the third thoracic spine. The LT electrode was placed obliquely upward and laterally along a line between the intersection of the spine of the scapula with the vertebral border of the scapula and the seventh thoracic spinous process.4,8,9,11 The last set of surface electrodes was applied on the SA parallel to the muscle fibers, below the axilla, anterior to the latissimus dorsi, and posterior to the pectoralis major.12,28-30 A reference electrode was placed over the clavicle. In all of the subjects, the dominant arm was tested. Each set of bipolar recording electrodes from each of 4 muscles was connected to a Noraxon Myosystem 2000 electromyographic (EMG) receiver (Noraxon USA, Scottsdale, Ariz). The sampling rate was 1000 Hz. All raw myoelectric signals were preamplified (overall gain = 1000, common rate rejection ratio 115 dB, signal to noise ratio <1 ìV RMS [root mean square] baseline noise, filtered to produce a bandwidth of 10-1000 Hz). Testing Procedure We began by recording the resting level of the electrical activity of each muscle. Then, verification of EMG signal quality was completed for each muscle by having the subject perform maximal isometric contractions in manual muscle test positions specific to each muscle of interest.21,23 For the UT muscle, resistance was applied to abduction of the arm because Schludt and Harms-Ringdahl41 found this position superior to shoulder girdle elevation in activating the UT muscle. The MT muscle was tested by applying resistance to horizontal abduction in external glenohumeral rotation.23 For LT testing, the arm was placed diagonally overhead in line with the lower fibers of the trapezius. Resistance was applied against further elevation.23 Serratus anterior manual muscle testing was performed by resisting humeral elevation at an angle of 135° of forward flexion.8,23 Subjects performed three 5-second maximum voluntary isometric muscle contractions against manual resistance by the principal investigator (A.C.). A 5-second pause occurred between muscle contractions.13,19 A metronome was used to control duration of contraction. As a normalization reference, EMG data were collected during maximal voluntary contraction (MVC) for each muscle. After signal filtering with a low-pass filter (single pass, Butterworth, 6-Hz low-pass filter of the sixth order) and visual inspection for artifacts, the peak average EMG value over a window of 1 second was calculated for each trial. Further calculations were performed with the mean of the repeated trials as a normalization value (100%).