Does your shoulder ache after overhead activity? Is it getting worse and now restricting that activity? Has a period of rest apparently resolved the problem only for the pain to recur when you returned to sport? Chronic shoulder pain is unfortunately an all-too-common consequence of repetitive 'overhead activity', such as serving and smashing in tennis, freestyle or butterfly swimming, bowling in cricket, javelin or baseball throwing and above-shoulder weight-training exercises. Chronic pain in the 'overhead athlete' is usually the result of damage to the rotator-cuff muscles of the shoulder (a group of four, small, deeply situated, strap-like muscles). This article will look at how such repetitive damage is caused and how the athlete may be able to prevent it occurring in the first place.
Structure of the shoulder
The shoulder joint complex is in fact made up by four joints: the glenohumeral joint (the 'ball-and-socket' joint between the upper arm or humerus and the shoulder blade or scapula, that most non-experts consider to be the shoulder joint), the acromio-clavicular joint (the joint between the lateral end of the collar bone or clavicle and the scapula), the sternoclavicular joint (the joint between the medial end of the clavicle and the breast bone or sternum) and the scapulo-thoracic joint (the 'virtual' joint between the undersurface of the scapula and the chest wall). Problems at any of these four joints may result in ineffective function of the shoulder joint complex and consequently pain.
There is more movement possible at the shoulder joint than at any other joint in the body. Over 1600 positions in three-dimensional space can be assumed by the shoulder. The price to be paid for such an extreme range of movement is an inherent lack of stability. To achieve peak performance during overhead activity, there must be optimal balance between mobility and stability. It is well known that swimmers who over-stretch their shoulders in an attempt to increase the range of their stroke, without improving their functional stability, are at increased risk of injury to the rotator cuff. Tennis players and throwing athletes, activities that are essentially asymmetrical, tend to develop greater shoulder external rotation in their dominant shoulder and this is commonly associated with functional instability. Shoulder-injury prevention strategies need to focus on improving shoulder stability.
Impingement and the rotator cuff
The bony anatomy of the glenohumeral joint comprises a large ball (the head of the humerus) and small socket (the glenoid of the scapula) with the muscles of the rotator cuff and scapular rotating (stabilising) muscles acting as the most important dynamic stabilisers of the joint. The muscles of the rotator cuff envelop the glenohumeral joint itself, and comprise the supraspinatus, infraspinatus, teres minor and subscapularis muscles. Supraspinatus abducts the arm (moves it laterally away from the side of the body), infraspinatus and teres minor externally rotate the shoulder, and subscapularis is prin-cipally an internal rotator of the shoulder. Sitting above the cuff is the coracoacromial arch, made up of the coracoid and acromion bony processes of the scapula and a ligament connecting the two processes. As the arm is abducted away from the body or flexed (brought forward), 'impingement' or squeezing of the rotator cuff between the head of the humerus below and the coracoacromial arch above can occur. The healthy, conditioned rotator cuff functions effectively as an integrated unit to stabilise and depress the head of the humerus, opposing the action of the large deltoid muscle and thereby preventing impingement. Any overhead activity that involves the arm being taken often enough from below shoulder level to above shoulder level has the capacity to damage the rotator cuff. With repeated impingement, a poorly conditioned cuff can become damaged, and a cycle of cuff damage, impaired function, further impingement and worsening cuff damage is initiated.
This form of primary impingement is most commonly seen in weight trainers who over-emphasise the development of their 'prime moving muscles' (pectoralis major, latissimus dorsi and deltoid) at the expense of their rotator cuff. It seems to be increasingly common in athletes as they reach their thirties. Primary impingement is preventable and, if the cuff is appropriately conditioned, exercises such as behind-the-neck press, incline bench press and extended front laterals, will not lead to pain. Differences in the shape and bony configuration of the undersurface of the acromion may dispose an athlete to this particular injury. A Type II (curved) or Type III (hooked) acromion will reduce the effective space through which the supraspinatus tendon slides during abduction. Plain X-rays should enable these two variations to be identified.
Secondary impingement refers to impingement secondary to underlying glenohumeral instability, when the rotator cuff is fatigued by its efforts to keep the humerus centred on the glenoid and consequently allows the head of the humerus to ride up, reducing the subacromial space. This is probably the most common mechanism of cuff injury seen in younger athletes, particularly those with increased joint laxity, and is seen frequently in swimmers and throwers. The primary problem here is instability and, unless this is treated, pain will be ongoing and progressive.
A strong and healthy rotator cuff is essential to the overhead athlete. In recent years, the role of the scapula-stabilising muscles in positioning the glenohumeral joint for optimal rotator-cuff function has been increasingly emphasised. Co-ordinated action of this group of muscles is needed to provide a stable base for pain-free overhead activity. The overly simplistic 'ball and socket' model of the shoulder joint has been superceded by a model similar to the performing seal that can balance a ball on its nose. The seal equates to the scapula, and constant small adjustments by the seal (scapula) are needed to prevent the ball falling off its nose (glenoid). Overhead athletes must be able to effectively control the position of their scapula for optimal cuff function.
Injury prevention strategies
Most cuff injuries can be prevented relatively simply. The crucial point is not to overwork the rotator cuff by increasing shoulder work too rapidly. Keeping increases in workload to less than 10% per week will significantly reduce the risk of injury. The important balance between stability and range of shoulder movement has already been emphasised. Athletes with access to sports medicine support will benefit from a formal assessment of dynamic shoulder function.. This should encompass a comprehensive review of static and dynamic anatomy, range of motion at all four joints of the shoulder joint complex, muscle strength and balance (particularly of the rotator cuff and scapular stabilisers) and an assessment of inherent glenohumeral stability in all three planes. Significant abnormalities detected need to be address and corrected. Such screening is becoming increasingly routine for the more elite overhead athlete and validated assessment and treatment protocols have been defined. Technique should be evaluated by the coach and appropriate technical changes integrated into the rehabilitation programme.
The role of the kinetic chain
Increasingly, the role of force generation by other body components is being assessed. For instance, the power generated by the shoulder in the tennis serve has been preceded by power generated by the legs, trunk and back. The muscle mass of the shoulder is relatively small, and if inadequate power is generated by the preceding links in the kinetic chain the shoulder has to play 'catch-up' and generate power rather than acting as a force regulator. Improving the server's leg action, lumbar strength and trunk rotation during the serve will reduce the incidence of rotator-cuff injury. Such biomechanical analysis is difficult but, in skilled hands, is a crucial and effective element in injury prevention.
How can an athlete prevent injury?
Although shoulder rehabilitation protocols after injury need to address subtle muscle imbalances and joint restrictions, and thus need supervision, isolated rotator-cuff strengthening exercises can be very effective as part of a pre-participation conditioning programme and can be done using the following three simple exercises. The key is to strengthen the internal rotator (subscapularis), external rotators (infraspinatus and teres minor) and abductor (supraspinatus) muscles of the shoulder. This is most easily and safely done using the variable resistance of a cliniband - a length of flat rubber available from large chemists in varying resistances. You will need about two metres; start with the lowest resistance and work up!
To strengthen the right scapularis muscle, start by holding your right arm by the side of your body with your elbow bent/flexed at 90 degrees (the forearm will be at right angles to the upper arm and the line of the forearm points forward). Attach or loop one end of the cliniband over a door handle to the right of your body and hold the other end in your right hand. Internally rotate your humerus against the resistance of the cliniband (seen from above the forearm moves in an anti-clockwise direction towards the left) while keeping your elbow bent at 90 degrees and at the side of your body. Let your forearm return to its starting position by the pull of the cliniband in a controlled fashion.
The external rotators are strengthened by the opposite action. From the same starting position but with the cliniband looped over a door handle to your left, externally rotate your right humerus against the resistance of the cliniband (seen from above the forearm moves in a clockwise direction to the right) while the elbow is again kept to the side of the body at 90 degrees. The forearm is again allowed to return to the starting position in a controlled fashion. Single sets comprise a minute of either external or internal rotation exercises and can be repeated three to five times a day. The cliniband needs to follow you around during the day! To strengthen the internal and external rotators of the left shoulder requires similar but mirror-image manoeuvres.
Supraspinatus conditioning requires abduction work and initially should be performed below shoulder level. The starting position is quite different from the previous two exercises. To strengthen your right supraspinatus, place one end of the cliniband under your left foot and extend (keep straight) your right elbow. Hold the other end of the band in your right hand and then internally rotate your right arm so that your right thumb points towards the floor and the back of your right hand faces forwards. Then, keeping your elbow extended, move your right arm away from your body (keeping the elbow straight) against resistance to just below shoulder level, and then let it return to the starting position in a controlled fashion. An easy refinement is to combine pure abduction with a little flexion so that you bring the arm forward as you move it away from your side.
Pinch your scapulae together
Pain should not be felt during any of the three exercises. Three-to-five minute sets over the course of a day will produce a conditioning effect. By shortening the length of the band you will be able to progressively increase resistance. There are a huge number of variations on the exercises described which achieve similar conditioning gains, and I make no claims for the superiority of the chosen three. However, they have worked well in my clinical practice and rarely cause unanticipated problems. Similar exercises can be carried out using the pulley systems found in most gyms and with further adaptations can be done with free weights. Maintaining scapular retraction (the scapulae are 'pinched together' towards the middle of your back and 'pushed down') while carrying out these exercises enables you to develop your scapular stabilising muscles at the same time.
Strengthening the scapular stabilisers without expert supervision is more difficult, but there is benefit in integrating wall leans (standing push ups against a wall), knee push ups and regular push ups in any conditioning programme. Seated rowing will strengthen the latissimus dorsi and should be undertaken while attempting to maintain scapular retraction.
A recent clinical supplement to Medicine & Science in Sports & Exercise, vol. 30 (4), April 1998, provides an excellent overview of the diagnosis, investigation and treatment of sporting shoulder injuries.