Swimmer’s Shoulder Part 1: Aetiology

Author: Becki Knight, Sports Physiotherapist, PhysioKinetic

Swimmer’s shoulder is characterised by pain in the anterior lateral aspect of the shoulder, although sometimes symptoms can migrate down the arm and into the posterior aspect of the glenohumeral joint. It is believed that swimmer’s shoulder is due to subacromial impingement involving the rotator cuff tendon, bicipital tendon, or subacromial bursa.

So why are swimmer’s at risk?

Swimmer’s often present with hypermobile shoulders- specifically increased anterior glenohumeral laxity. So as with overhead athletes, they present with excessive external rotation and limited internal rotation. This greater range of external rotation places greater demand on the rotator cuff and the long head of the biceps to prevent elevation and anterior translation humeral head. Any failure of the rotator cuff or scapular stabilizers to maintain the position of the humeral head can lead to excessive humeral head migration and either increased load on the tendons or compression of the tendons between the humeral head and acromian. It is likely that a combination of both exists in swimmer’s presenting with shoulder pain.

So why does this happen?

The causes are likely multi-factorial and are thought to be a result of a combination of: –

• impaired posture
• impaired glenohumeral joint mobility-specifically internal rotation
• poor stroke technique ( impaired neuromuscular control or proprioception-depending on your terminology!!)
• reduced muscle performance (either activation or strength)
• overuse/inadequate recovery-training errors

However if we analyse the free-style swimming technique it gives us some insight into the potential reasons as to why swimmers are so at risk from these symptoms

So what happens during a free-style swimming stroke?

The stroke is split into 2 main phases- Pull through (early, mid and late) and Recovery (elbow lift, mid and late) (Richardson et al, 1980; Souza, 1994). More simply-catch, pull, and recovery. The table below gives an insight into both the kinematics and muscle action during these phases.

Phase		Muscle Action	Kinematics GH Jt	Kinematics Scapula
Catch	Hand enters water	Upper trapezius and the rhomboids. The serratus anterior protracts, rotates the scapula up, and is highly active from this point in the catch and through the pull. These opposing actions hold the scapula in place.	External rotation and abduction	Upward rotation and retraction
Pull		Just after the catch, the pectoralis major adducts the humerus while internal rotation is balanced by the antagonistic external rotation of the teres minor. The latissimus dorsi and subscapularis activate from mid pull.	Internal rotation and adduction	Downward rotation and adduction
Recovery	Hand leaves water	The deltoid and supraspinatus are the prime movers through recovery.	External rotation and abduction	Protraction and upward rotation

So what implication does this have?

We can see from the table that the free style stroke will increase strength in the shoulder adductors, extensors and internal rotators. In fact swimmers often show a reduction in their external to internal rotator endurance ratios (Fowler, 1990). Falkel et al. (1987) argued that this ratio was correlated to shoulder pain in swimmers. They also postulated that when the ratio of external rotator to internal rotator endurance dropped below 50% the swimmer no longer had sufficient endurance to maintain optimal stroke mechanics during the recovery phase thus increasing the risk of subacromial pain. Pink et al (1996) argued weakness in serratus anterior and increased rhomboid activation during the pull to be responsible for pain in swimmers. They hypothesised that this muscle imbalance causes impingement of the biceps tendon and supraspinatus due to altered scapula kinematics.

Another key contributing factor for swimmers is the volume of training that is undertaken compared to other overhead sports. Johnson et al, (1987) assessed the training habits of several upper limb dominant sports. They reported that on the average shoulder revolutions per week of a golfer, javelin thrower, baseball pitcher and swimmer (see table below).

Sport	Revolutions per week	Injury incidence at Clinic
Golf	200	7%
Javelin Thrower	300	29%
Baseball Pitcher	1000	57%
Swimmer	16000	66%

These statistics may have actually been too conservative as Kammer, Young, Niedfeldt (1999) calculated that highly competitive swimmers actually perform more than 1 million shoulder revolutions per week. The implications for this are significant given that shoulder injuries are occur 30% and 38% of all swimming injuries per year (Bak et al, 1989 & Cole et al 2002). In fact, McMaster and Troup (1993) reported a lifetime shoulder injury incidence of 47% to 73% for competitive swimmers.

Rehabilitation and injury prevention.

 Treatment and prevention of this condition has historically focused on addressing high risk factors associated with the condition. Continual analysis of swim stroke is paramount to ensure that stroke mechanics are optimised for performance and injury prevention.

Exercises aimed at addressing deficits in muscle and joint function are the main stay of managing this condition. An example of common rehabilitation goals are:-

• improve glenohumeral joint instability
• reduce posterior capsule restrictions
• improve muscle endurance specifically serratus anterior and subscapularis

A follow up article will focus on discussing rehabilitation strategies and exercise prescription.

 

References

Bak K, Bue P, Olsson G: Injury patterns in Danish competitive swimming. Ugeskr Laeger 1989;151(45):2982-2984

Cole A, Johnson JN, Fredericson M: Injury incidence in competitive swimmers. Presented at USA Sports Medicine Society and American Swim Coaches Association meeting; September 7, 2002; Las Vegas

Kammer CS, Young CC, Niedfeldt MW: Swimming injuries and illnesses. Phys Sportsmed 1999;27(4):51-60

McMaster WC, Troup J: A survey of interfering shoulder pain in United States competitive swimmers. Am J Sports Med 1993;21(1):67-70.

Pink M, Jobe F: Biomechanics of swimming, in Zachazewski JE, Magee DJ, Quillen WS: Athletic Injuries and Rehabilitation. Philadelphia, Saunders, 1996, p 317

Souza TA: The shoulder in swimming, in Sports Injuries of the Shoulder: Conservative Management. New York City, Churchill Livingstone, 1994, pp 107-24