What is it?
For those of you that are not familiar with the term swimmers shoulder it is a painful shoulder condition with or without loss of range of movement, that is common in competitive swimmers which can also present as pain in the upper arm and neck. It is most commonly a chronic condition with a gradual onset and occurs with a prevalence of 40-91% in competitive swimmers at some point in their swimming career.
What It Causes
It is a condition caused by repetitive movements of the shoulder and with top swimmers averaging around 4000 plus revolutions of the shoulder per day, the better you get the more likely it is you’ll suffer from this frustrating and painful condition. It also tends to effect female swimmers slightly more than male swimmers and this is thought to be because female swimmers in general have shorter arms and thus tend to have a shorter distance per stroke doing more strokes per session than male swimmers. It also tends to occur more in freestyle and butterfly swimmers as it is linked to overhead movements and is similar to injuries sustained by other overhead athletes, like baseball pitchers.
Why Does It Happen
Well to answer that question we need to go into a bit of shoulder anatomy.
The shoulder joint is a ball and socket joint with the head of the humerus (upper arm bone) forming the ball and the glenoid fossa of the scapular (shoulder blade) the socket. The socket is relatively shallow compared to the hip joint which gives the shoulder a far greater range of movement but at the expense of stability. Above the shoulder joint there is a small space created by the humeral head and a bony prominence on the scapular called the acromion, which contain two muscles, supraspinatus and the long head of biceps and a bursa (a fluid sac that acts as a cushion between bones and tendons).
The shoulder joint itself is surrounded by a joint capsule and a group of four muscles called the rotator cuff (supraspinatus, infraspinatus, teres minor and subscapularis). When the upper arm is lifted, especially in abduction (to the side) the rotator cuff muscles must work to slide the humeral head downwards as it roles in the glenoid fossa to maintain space the two muscles and the bursa or these will become pinched (impinged), which is known as subacromial impingement. To aid in this motion the scapular also rotates so that the glenoid fossa and the acromion move to face upwards to allow for further movement of the upper arm without impingement, this movement is controlled by the actions of serratus anterior and trapezius muscles.
Swimmers need to have very mobile shoulder joints to perform the ROM necessary to move through the water efficiently. As an adaption to this pressure to develop increased ROM of the shoulder they tend develop joint capsule laxity which puts put even more reliance on the rotator cuff to stabilise the humeral head and keep it within the glenoid fossa. This and the high frequency of rotations preformed can contribute towards swimmers shoulder in the following ways.
It is likely that all three of these contribute towards swimmers shoulder. However, in cases where pain is felt more acutely in the ‘catch’ phase of the swimmers stroke when the swimmer starts their pull, microtrauma of the rotator cuff may be larger factor. If pain is felt during the recovery phase of the stoke as the arm come over the water, subacromial impingement is perhaps slightly more likely.