Article Review — Electromyographic analysis of specific exercises for scapular control in early phases of shoulder rehabilitation

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Study Title:  Electromyographic analysis of specific exercises for scapular control in early phases of shoulder rehabilitation

Authors:  Kibler WB, Sciascia AD, Uhl TL, Tambay N & Cunningham T

Publication Information:  American Journal of Sports Medicine 2008; 36(9): 1789-1798.

Summary:

Recently there has been much attention in clinical and exercise rehabilitation research on scapular movement as it relates to shoulder girdle function and injuries. Specifically, it is now widely accepted that scapular dyskinesis (SD), encompassing alterations in static scapular position and loss of dynamic control, relates directly to the development and proliferation of many shoulder conditions.  In general, SD results in increased anterior tilt, decreased upward rotation, and increased internal rotation of the scapula. Together, these changes have been shown to alter the function of the joint by:

– altering normal scapulohumeral rhythm

– increasing tension in the anterior inferior glenohumeral ligament

– decreasing subacromial space with arm abduction

– inhibiting supraspinatus muscle activity

In a normal shoulder, specific patterns of muscle activation position the scapula to optimize the spatial relationship between the stable trunk and the mobile glenohumeral complex during movement. These muscle activation patterns have been shown to be altered in injured shoulders1. As such, rehabilitation of these deficits should be integral in any shoulder rehabilitation program.  Early rehabilitation of most shoulder conditions focuses on scapular control. The goal of these  protocols should be to restore retraction of the scapula – a position of posterior tilt and external rotation. However, many exercises often employed in early rehabilitation are difficult to achieve for many injured shoulders as they require high degrees of arm elevation, glenohumeral rotation, or forward flexion/scapular protraction.  The goal of this study was to investigate the amplitude and sequence of muscle activation with specific exercises that can be used safely in early rehabilitation protocols. 39 subjects (average age ~ 30) were studied – 18 who were asymptomatic for shoulder pain, and 21 with shoulder pathology diagnosed by the first author (WBK) as impingement (n=9), labral injury (n=5), or rotator cuff tendinopathy (n=7), all of whom demonstrated scapular dyskinesis on clinical examination. Subjects were excluded from the study if they had any neurological condition or had previous shoulder surgery.

Four exercises were performed (described below) while EMG recordings (MVC normalized) were gathered from the following muscles: the upper trapezius (UT), lower trapezius (LT), serratus anterior (SA), anterior deltoid (AD), and posterior deltoid (PD). The UT, LT, and SA were selected because they are considered the most important muscles in the force couples that govern scapular motion.

The exercise protocol included the following exercises (with targeted muscles):

1) Inferior Glide (SA/LT) – is an isometric exercise that emphasizes humeral head depression and scapular retraction. In a sitting position, the arm is placed in 90° of abduction on a supportive surface. The subject then applied force through their fist (which was resting on the surface) in an adduction direction while inferiorly depressing their scapula for 5 seconds.

2) Low Row (SA/LT) – was performed as an isometric exercise emphasizing scapular external rotation and posterior tilt. With the arm at the side, subjects placed their hand on the anterior edge of a surface (ex. a table) with their palm facing posteriorly. They were then instructed to extend their trunk and push their hand into the surface in the direction of shoulder extension while maintaining retraction and depression of the scapula for 5 seconds.

3) Lawnmower (SA/LT) – is a multi-joint exercise performed with the subject standing with the trunk flexed forward and rotated contralateral to the arm performing the motion (hand at opposite patella) – subject the rotates the trunk, extends the hip and trunk to vertical, and attempts to put their elbow in their back pocket (hence retracting and depressing the scapula) – this motion mimics starting a “pull lawnmower”.

4) Robbery – is a multi-joint exercise that uses hip/trunk extension and bilateral arm motion to induce scapular retraction. The subject stands with the trunk forward flexed roughly 50° with arms forward (hands facing thighs). Then the trunk and hips are extended while pinching both scapulae toward the “back pockets” for a 5 second contraction.

Pertinent results of this study include:

– there were no significant differences in muscle activation between symptomatic and asymptomatic subjects

– the SA and LT were activated between 15-30% for all exercises – an amplitude known to provide strength gains

– UT activity was higher (21-36%) in the lawnmower and robbery exercises

– the inferior glide and low row, both safe to perform very early in rehabilitation, activated the SA/LT adequately to provide strength gains

– when the scapula begins in a retracted position (as in the low row) – the SA is activated early – when retraction occurs later in the motion (as in the lawnmower and robbery), the SA is activated last

– the trapezius showed task-specific patterns: when the shoulder begins in a closed-chain position (as in the inferior glide and low row), the trapezius (UT and LT) activate later; in the open chain exercises, the UT/LT become active sooner (see below for clinicalapplication)

Conclusions and Practical Application:

The exercises evaluated in this study are effective in sufficiently activating key scapular stabilizing muscles in task-specific patterns. This suggests that these exercises may be used in early and middle phases of a comprehensive shoulder rehabilitation program.  Clinicians and exercise specialists should focus on the LT/SA force couple, which is responsible for reducing a common finding in scapular dyskinesis – inferior/medial scapular border prominence. The astute clinician will recognize that de-emphasizing activation of the UT (the “shrug”) is a key in this type of rehabilitation. The results from this study suggest that the two closed-chain exercises (inferior glide and low row) create a muscle activation pattern that limits UT activation while stimulating the LT/SA in a manner that does not impinge the shoulder – making these exercises more useful very early in the program. The open-chain exercises may best be used a bit later in the program, as they incorporate dynamic patterns and larger motions that generate more joint shear.

NOTE: the authors acknowledge that the exercises chosen for this study are but a few of the possibilities for this type of rehabilitation. Future research will continue to elaborate on muscle activation patterns of other exercises to guide evidence-based implementation of this type of exercise.

Additional References:

1) Cools AM et al. Isokinetic scapular muscle performance in overhead athletes with and without impingement symptoms. Journal of Athletic Training 2005; 40(2): 104-110.

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