Rotator cuff strengthening - treating and preventing shoulder injury

Nagging shoulder pain can sideline an athlete for a season or more. As Alicia Filley explains, to remain competitive and keep symptoms from progressing, rotator cuff strengthening must be an integral part of an athlete’s training programme; especially those who frequently use overhead arm movement in their sport.At a glance:

• The anatomy and function of the shoulder complex is full explained
• The signs and symptoms of a stressed shoulder are assigned to the varying stages of injury
• A portable and practical exercise programme for optimal shoulder health is given.

The shoulder

Consisting of four muscles and their tendons, the ‘rotator cuff’ provides connection, protection, and mobility to the shoulder joint. It attaches the humerus to the scapula, and forms a ring or cuff around the joint that helps prevent the bone from slipping out of its shallow socket called the glenoid fossa. The muscles of the rotator cuff, the subscapularis, the infraspinatus, the teres minor, and the supraspinatus, are often referred to by the acronym SITS muscles (see figure 1).

The subscapularis originates on the front of the scapula and attaches to the upper humerus. It is the only rotator cuff muscle to be located on the anterior portion of the shoulder joint and resists motion of the humeral head in the forwards direction. It functions primarily to rotate the arm inward.

The supraspinatus originates on the posterior (rear) aspect of the scapula above the scapular spine, courses underneath the coracoacromial ligament, and attaches to the top of the humerus. The supraspinatus tendon is the most commonly involved tendon in rotator cuff pathology and understanding the anatomical placement of this tendon is important(1). Between this tendon and the coracoacromial ligament is the ‘subacromial bursa’, which acts as a cushion to the supraspinatus tendon. This complex architecture leaves little room for variability without one structure affecting its neighbour.

The infraspinatus muscle is located below the spine of the scapula and teres minor originates below it, along the lateral border of the scapula. Both tendons pass over the posterior portion of the shoulder joint and insert on the backside of the arm bone. The role of these muscles working together is to externally rotate the arm and assist the supraspinatus in stabilising the humeral head during arm elevation.

Rotator cuff biomechanics

The rotator cuff functions straightforwardly in the internal and external rotation of the arm. However, its function as a humeral head stabiliser is more complex. For example, try moving your arm away from your side with your palm facing down. In this position the shoulder cannot extend past 90 degrees of abduction. As the deltoid muscle abducts the arm, it also elevates the humerus, which butts against the acromion of the scapula and can go no further.

Now turn your palm upward and you are able to complete the range of motion overhead. The infraspinatus and the teres minor function to externally rotate the arm and, along with the supraspinatus, draw the humeral head inward and down, thus clearing the acromion and allowing the arm to abduct to 120 degrees (see figure 2). At that point, the scapula begins to rotate away from the spine, effectively extending the position of the shoulder in space, moving the acromion away from the head of the humerus, and allowing the arm to abduct the remaining 60 degrees(2). Therefore, complete range of motion in the shoulder requires synchronous activation of the rotator cuff with the other shoulder muscles.

Impingement syndrome

While athletes can suffer an acute rotator cuff tear as a result of a traumatic event, chronic rotator cuff conditions usually start with a tendonitis of the supraspinatus muscle. The term ‘impingement syndrome’ refers specifically to the irritation of the supraspinatus tendon as it repeatedly butts against the underside of the acromion during movement. As the anatomy in this region is very precise, the presence of a bone spur, anomaly in the shape of the acromion, or weakness in one of the rotator cuff muscles, can easily result in an impingement of the tendon when the arm is raised overhead.

The impingement causes inflammation of the offended tendon as well as the bursa that lies above it. The greatest impingement occurs with the arm reaching forward and internally rotated. This is the position after release in throwing, when the rotator muscles are contracting eccentrically, and at the beginning of pull-through phase in freestyle swimming, when the rotator cuff muscles are working concentrically.

A ‘secondary’ impingement syndrome can be caused by shoulder instability(2). Laxity in the shoulder ligaments means that when the arm moves, the head of the humerus does not stay snugly depressed within the glenoid fossa. This increased range of motion affects the length-tension relationship of the rotator muscles, impairing their ability to stabilise the humeral head in the socket(1). This applies particularly to swimmers, who often demonstrate increased shoulder range of motion.

Repeated overhead movements can also irritate the tendon and produce an inflammatory response. The cramped anatomy only compounds the situation as an inflamed tendon now becomes pinched under the coracoacromial ligament. While rotator cuff injuries are degenerative in nature and their incidence increases with age, the sustained overuse of the shoulder in athletes seems to speed up the process. For instance, estimates suggest the average American collegiate swimmer performs more than one million strokes per year with each arm(1)!

Classification of disease and swimming

Physicians in Canada have divided the spectrum of rotator cuff disease into three stages(3). The first stage, which usually affects athletes aged 25 and under, is bruising and swelling in the rotator cuff tendons as a result of microtrauma from overuse. The athlete may complain of a dull ache or tenderness at the very top of the shoulder joint, and experience pain as he moves the arm away from the body. Injury at stage I is usually reversible with rest and conservative treatment.

In overhead athletes, swimmers are the most susceptible to shoulder strain because of the constant motion and arm strength required. A swimmer’s arms perform 90 percent of the propulsion during swimming(2). Because of this, the small muscles of the shoulder are vulnerable to fatigue. The first to tire in swimmers with non-painful shoulders is usually the subscapularis.

In swimmers with shoulder pain, the subscapularis may fatigue earlier, or diminish function to avoid pain during internal rotation at pull-through. Scapular stabilising muscles may also be weak, interrupting the normal scapular-humeral rhythm required for full shoulder range of motion. With a painful shoulder, a swimmer may exhibit early hand exit, a dropped elbow during recovery, or a wider hand entry(2). Coaches and trainers should be attuned to these subtle signs of stage I injury and avoid assigning ‘lazy’ swimmers more laps to fix the problem.

Stage II injury is primarily seen in athletes age 25 to 40. At this point, the tendons of the rotator cuff are inflamed, thickened and fibrotic. The aching pain in the shoulder becomes more prevalent, often increasing at night, and inhibiting performance of the offending athletic manoeuvre. Swimmers with increasing pain may demonstrate an asymmetric pull and have difficulty staying in the centre of the lane. Changes in the beat of kicking or an increase in body roll may be compensatory strategies to avoid pain in the shoulder. If any of these compensations are noted, a swimmer should be pulled immediately from a workout and tested for shoulder injury. Once the injury reaches stage II, rest alone is unlikely to heal the shoulder. Treatment often includes physiotherapy, exercises, and cortisone injections.
At the age of 40, the risk for developing a stage III injury increases significantly. The combination of years of overuse, as well as the degenerative changes associated with age leave the rotator cuff more vulnerable. Partial tears can occur in the tendons and a seemingly minor incident can result in a complete tear. Pain occurs as before, usually with associated limitations in shoulder range of motion. Surgical intervention is usually necessary.

Staying strong

Greek researchers sought to find the most effective way to train the rotator cuff muscles and restore strength balance around the shoulder joint(3). When comparing training methods of multi-joint dynamic resistance exercises, isolated dumbbell training, and isokinetic exercises, they found all interventions improved the muscle balance around the joint when compared to controls. However, the best results were with the isokinetic programme.

Seeking a more practical method of training, researchers at the University of Pittsburgh examined on-field, resistance-tubing exercises for throwing athletes(4). After evaluating EMG data from the shoulder muscles of athletes performing 12 different exercises, they concluded that performing seven of the exercises activated all the important muscles for throwing. Though these results are specific to throwing, all overhead athletes, including swimmers, utilise the same muscles in similar movement patterns.

While studies conclude that any programme to strengthen the shoulder will yield positive results, researchers at Northeastern University in Boston, sought the most specific exercise for the supraspinatus muscle(5). EMG data revealed that the ‘full can’ exercise in standing, performed in the scapular plane, proved to be the most effective (see figure 5).

Of course, the key to any training programme is doing the exercises correctly and in a focused manner. Special attention must be paid to the stretching component of the programme. Frontal shoulder capsule mobility is rarely a problem in overhead athletes. Making the front of the shoulder more mobile only increases the vulnerability of the rotator cuff. In fact, one pair of authors contend that knowing which shoulder stretches not to do is more important than doing any at all(6)! The wall stretch and the partner stretch (pulling the arm from behind) should be eliminated from every athlete’s programme! Making sure athletes are individually instructed will avoid risky training techniques.

Alicia Filley, PT, MS, PCS, lives in Houston, Texas and is vice president of Eubiotics: The Science of Healthy Living, which provides counselling for those seeking to improve their health, fitness or athletic performance through exercise and nutrition.

References

1. Clin Sports Med. 2001 Jul;20(3):491-503
2. Orthop Clin North Am. 2000 April;31(2):295-311
3. Br J Sports Med. 2004,38:766-772
4. J Athl Train. 2005;40(1):15-22
5. J Athl Train. 2007;42(4):464-469
6. Orthop Clin North Am. 2000 Apr;31(2):247-61