The Epidemiology and Pathogenesis of Swimmer's Shoulder¶
Shoulder pain is the most commonly reported musculoskeletal complaint in competitive swimmers, with prevalence rates estimated to range from 40% to 91% across various populations. The condition, often referred to as "swimmer's shoulder," is primarily attributed to overuse mechanisms resulting from the extraordinary repetitive demand of training; elite athletes may perform up to 1.5 million stroke cycles per arm annually. Despite advancements in understanding, the injury burden has shown no significant reduction since the 1980s, and shoulder injuries remain the leading cause of missed or modified training time.
The epidemiology of these injuries varies significantly across different age groups and ability levels:
Epidemiology by Age Group¶
Youth Swimmers (\<14--15 years):¶
This group typically reports the lowest prevalence of shoulder pain, with rates cited between 19% and 20%. At this stage, injury risk is often linked to scapular dyskinesia, periscapular muscle weakness, and core endurance deficits. Interestingly, in male youth swimmers, the relationship between shoulder strength and swimming performance is fully mediated by biological maturation, suggesting that growth is a more significant factor than strength assessment during these years.
Knowledge Check
This demographic experiences rates up to 91.3%, attributed to the transition to high training volumes during periods of rapid physical growth.
Adolescent Swimmers (15--17 years):¶
This demographic experiences the highest rates of shoulder pain, reaching up to 91.3%. This peak is attributed to the transition to high training volumes (often twice-daily practices) during periods of rapid physical growth, which can overload soft tissues. Adolescent females may be particularly susceptible to acute muscle imbalances following a single training session compared to their male counterparts.
Knowledge Check
The combination of transitioning to high training volumes (often twice-daily practices) during periods of rapid physical growth can overload soft tissues.
Adult and Collegiate Swimmers (18--22/27 years):¶
In collegiate settings, shoulder injuries account for 27% of all reported injuries. Data from NCAA men's programmes show an injury rate of 1.56 per 1,000 athlete-exposures. While these athletes handle the highest absolute volumes, they may be better adapted to the load than adolescents; however, preseason functional scores (such as the KJOC) are significant predictors of their end-of-season performance.
Masters Swimmers (>27 years):¶
Reported prevalence is lower than adolescents, at approximately 19.4%. Unlike younger cohorts, some studies suggest a negative association in Masters swimmers where lower training volumes are related to higher pain levels, potentially due to deconditioning or age-related tissue changes.
Epidemiology by Ability Level¶
Elite and National Swimmers:¶
These athletes possess superior baseline physical qualities, such as greater shoulder rotator torque, which may protect against acute drops in performance after training. However, asymptomatic structural abnormalities are nearly universal in this group; MRI and ultrasound studies have found supraspinatus tendinopathy in 70--93% and subscapularis tendinopathy in 73% of elite swimmers' shoulders. These findings are often considered normal adaptive changes rather than active pathologies.
Knowledge Check
MRI and ultrasound studies have found supraspinatus tendinopathy in 70-93% and subscapularis tendinopathy in 73% of elite swimmers' shoulders. These findings are often considered normal adaptive changes rather than active pathologies.
University and Club Swimmers:¶
Compared to elite counterparts, university-level swimmers often have lower load capacity and experience greater drops in shoulder force and range of motion after high-intensity sessions. This lower tolerance for maintaining loads may put them at a higher relative risk of injury when training intensity is increased.
Common Risk Factors and Pathogenesis¶
The development of injury is multifactorial, involving extrinsic factors like hand paddle use, inconsistent training loads, and sudden spikes in volume. Intrinsic factors include Glenohumeral Internal Rotation Deficit (GIRD), found in 18% of young elite swimmers, and scapular dyskinesis, which alters the subacromial space. While traditional models focused on subacromial impingement, newer research highlights the prevalence of internal impingement (specifically Antero-superior Internal Impingement) driven by repeated loading in high degrees of elevation and internal rotation.
Pathological Presentations and Clinical Classifications of Swimmer's Shoulder¶
Patient presentations for "swimmer's shoulder" are diverse because the term serves as an umbrella for a spectrum of coexisting or consecutive pathologies rather than a single diagnosis. While prevalence is high, many athletes present with asymptomatic structural changes on imaging, such as supraspinatus tendinopathy in 70--93% and subscapularis tendinopathy in 73--80% of elite swimmers, which may represent normal physiological adaptations to training rather than active pathology.
Typical patient presentations can be categorised by the following usual pathologies:
1. Subacromial (External) Impingement¶
• Subjective Report: Swimmers typically report a gradual onset of pain located at the anterior or lateral aspect of the shoulder.
• Clinical Presentation: Pain is often elicited during a painful arc of active movement and is reproduced by clinical tests like the Neer sign or Hawkins-Kennedy test, which compress the supraspinatus tendon and subacromial bursa against the coracoacromial arch.
• Classification: This is often defined as Type A Swimmer's Shoulder, characterized by isolated bursitis and supraspinatus inflammation without instability.
2. Internal Impingement (ASII and PSII)¶
• Subjective Report: Patients often experience deep shoulder pain that occurs specifically during the initial catch and early pull-through phases of the freestyle stroke.
• Clinical Presentation:
◦ **Antero-superior Internal Impingement (ASII):** Pain is provoked
by flexion and internal rotation, where the deep surface of the subscapularis and the biceps pulley impinge against the anterior-superior glenoid rim.
◦ **Posterior-superior Internal Impingement (PSII):** Often presents
as pain at the posterior aspect of the shoulder during the late recovery or early catch phase.
• Classification: This corresponds to Type B Swimmer's Shoulder, involving labral fraying and articular-side rotator cuff lesions.
3. Labral Injuries and Instability¶
• Subjective Report: Swimmers may report a "dead arm" sensation when using the arm overhead, or a clicking/catching sensation deep within the joint.
• Clinical Presentation:
◦ **Clicking from the back** of the shoulder may indicate a
posterior labral tear, while clicking at the front may relate to the long head of the biceps.
◦ **Instability:** Many swimmers present with **multidirectional
laxity**; however, pathological instability (Type D) is often asymptomatic unless it leads to secondary impingement.
◦ **Apprehension Sign:** This is frequently positive in **135
degrees of elevation** rather than the standard 90 degrees, reflecting the vulnerable position at the start of the pull-through.
4. Scapular Dyskinesis and Postural Imbalances¶
• Subjective Report: Swimmers may experience early fatigue during sessions, which coaches might observe as a "dropped elbow" during the recovery or pull-through phases.
• Clinical Presentation:
◦ Typical features include **rounded shoulders, forward head
posture**, and an enlarged thoracic kyphosis.
◦ On examination, the scapula often appears **protracted, abducted,
and anteriorly tilted**.
◦ The **Scapular Assistance Test** or **Scapular Retraction
Test** often provides immediate relief of pain during active movement, suggesting the scapula is failing to maintain a stable base for the humerus.
5. Suprascapular Neuropathy¶
• Subjective Report: Swimmers, particularly backstrokers, may present with unexplained weakness or dull aching.
• Clinical Presentation: This is often linked to a dropped elbow during the pull-through and reduced body roll, which places traction on the suprascapular nerve as it passes through the suprascapular notch.
6. Muscle Imbalances (GIRD and Ratios)¶
• Subjective Report: While not a "pain" presentation itself, it is a precursor; swimmers often have 40 degrees less internal rotation than non-swimmers.
• Clinical Presentation:
◦ **Glenohumeral Internal Rotation Deficit (GIRD):** Defined as a
loss of IR in the dominant arm of 20 degrees or more compared to the non-dominant side, often coupled with a tight posterior capsule.
◦ **Strength Imbalance:** A **low eccentric external rotation to
concentric internal rotation ratio** (\<0.68) is a significant predictor of in-season injury.
Knowledge Check
GIRD is defined as a loss of internal rotation in the dominant arm of 20 degrees or more compared to the non-dominant side, often coupled with a tight posterior capsule.
Knowledge Check
The Apprehension Sign is frequently positive in 135 degrees of elevation rather than the standard 90 degrees, reflecting the vulnerable position at the start of the pull-through.
Clinical Pathways for Swimmer's Shoulder Management¶
The optimal care pathways for the common pathological presentations of "swimmer's shoulder" prioritise conservative management, as surgical outcomes often show low return rates to pre-injury performance levels. Treatment is generally structured into three phases: Phase 1 (active rest and technical correction), Phase 2 (restricted swimming and anti-inflammatories), and Phase 3 (surgical consideration after 3+ months of failure).
1. Subacromial (External) Impingement (Bak Type A)¶
• Care Pathway: Management focuses on reducing inflammation in the subacromial bursa and supraspinatus tendon while correcting mechanics.
• Conservative Care: Active rest, ice after practice, and NSAIDs for up to one week are standard. Corticosteroid injections into the bursa should be reserved only for cases with constant, persistent pain.
• Surgical Pathway: If conservative efforts fail, arthroscopy with bursectomy and partial coracoacromial ligament release is indicated.
2. Internal Impingement (ASII and PSII) (Bak Type B)¶
• Care Pathway: Pathways for Antero-superior (ASII) and Posterior-superior (PSII) internal impingement should follow a tendinopathy model of rehabilitation, utilising a graded loading approach.
• Conservative Care: Exercises must target the scapular stabilizers and the rotator cuff. Coaches should encourage increased body roll and early initiation of external rotation during the recovery phase.
• Surgical Pathway: Debridement or repair of labral fraying and PASTA lesions (Partial Articular Surface Tendon Avulsions).
3. Labral Injuries and Instability (Bak Types C and D)¶
• Care Pathway: This is divided into Complex Impingement (Type C), which involves both intra- and extra-articular pathology, and Isolated Minor Instability (Type D).
• Conservative Care: Youth athletes particularly benefit from neuromuscular control exercises to optimise shoulder stability in the developing joint. Strengthening focuses on the core and posterior shoulder muscles to maintain the humeral head in the glenoid.
• Surgical Pathway: Type C requires a combination of labral/PASTA repair and capsular plication. Type D is typically managed with capsular plication alone. Surgery in these athletes is not for the feint of heart, and would almost never be a first line intervention.
4. Scapular Dyskinesis and Postural Imbalances¶
• Care Pathway: A 6--8 week targeted exercise program is effective in reducing pain and incidence.
• Specific Exercises: Pathways include push-ups with a plus (to engage the serratus anterior), scapular push-ups, shoulder taps, and serratus wall slides.
• Manual Therapy: The addition of myofascial release and joint mobilisations of the glenohumeral, cervical, and thoracic spines to a strengthening program has been shown to decrease pain more effectively than exercise alone.
5. Suprascapular Neuropathy¶
• Care Pathway: This presentation is often associated with technical errors that place traction on the nerve.
• Conservative Care: Coaches must correct the "dropped elbow" during the pull-through phase and ensure adequate body roll to reduce nerve strain.
• Surgical Pathway: Neurolysis for suprascapular neuropathy is one of the few surgical procedures in swimmers with high success rates for returning to prior training volumes.
6. Muscle Imbalances (GIRD and Ratios)¶
• Care Pathway: Pathways focus on restoring symmetry and eccentric strength to counteract the internal rotation (IR) dominance of the swimming stroke.
• Stretching (GIRD): Daily use of the "sleeper stretch" or "swimmer's stretch" is recommended to restore posterior capsule flexibility.
• Strengthening (Ratios): A land-based eccentric external rotation (ER) program targeting the infraspinatus is critical, as a preseason functional ratio below 0.68 is a major risk factor for in-season injury.
• Monitoring: Coaches are encouraged to regularly assess IR and ER torque to identify individual trends and adjust dryland volume accordingly.
Knowledge Check
The optimal care pathways prioritise conservative management, as surgical outcomes often show low return rates to pre-injury performance levels. Treatment is structured into three phases with surgery considered only after 3+ months of conservative treatment failure.
Knowledge Check
Neurolysis for suprascapular neuropathy is one of the few surgical procedures in swimmers with high success rates for returning to prior training volumes, particularly for backstrokers.
Comprehensive Screening Protocols for Swimmers' Shoulder Injury Prevention¶
A feasible and valid screening programme for competitive swimmers must address both extrinsic training factors and intrinsic physical qualities. Because the presentation of "swimmer's shoulder" is multifactorial, screening protocols should be tailored to the athlete's biological maturity, competitive level, and historical injury data.
1. Core Screening Components & Valid Tools¶
To be feasible in a clinical or poolside setting, the programme should utilize the following validated tools:
• Subjective Assessment: Use the Kerlan-Jobe Orthopaedic Clinic (KJOC) questionnaire. A high preseason KJOC score is a significant predictor of end-of-season performance.
• Strength Testing: Hand-held dynamometry (HHD) is a reliable and valid tool for measuring shoulder rotator strength and ratios when isokinetic testing is unavailable.
• Dynamic Stability: The Closed Kinetic Chain Upper-Extremity Stability Test (CKCUEST) is a low-cost, validated measure of functional performance.
• Range of Motion: Shoulder rotational ROM, Combined shoulder elevation (prone), thoracic spine rotation in sitting when performed skilfully can be helpful in monitoring individual athletes' responses to training loads.
• Biological Tracking: For youth athletes, the Mirwald method (estimating years from peak height velocity) is essential to distinguish between training-induced strength gains and growth-mediated development. Better, of course, is skeletal age but this requires hand/wrist X-Ray, and expert interpretation of these scans.
2. Normative Data and Cut-offs by Age Group¶
Youth Swimmers (\<14 Years)¶
• Core Endurance: A side plank/bridge time of \<8.5 seconds is identified as a risk factor for developing shoulder pain in this age group.
• Periscapular Strength: Deficits in middle trapezius strength are associated with pain in younger age groups (8--11 years).
• Biological Maturation: Strength assessments should be interpreted with caution, as maturation fully mediates the relationship between shoulder strength and performance in male youth swimmers.
Adolescent Swimmers (15--17 Years)¶
This group has the highest prevalence of pain (up to 91.3%) and is the most sensitive to training volume changes.
• Isokinetic Strength Ratios: A preseason functional ratio (eccentric ER to concentric IR) below 0.68 is associated with a 4.5-fold increased risk of in-season injury.
• Conventional Ratio: For injury prevention, the ER:IR ratio should be between 0.66 and 0.75 (external rotators having at least ⅔ the strength of internal rotators).
• Glenohumeral Internal Rotation Deficit (GIRD): Defined as an internal rotation (IR) loss of >18° compared to the non-dominant side, or an IR discrepancy of 20° or more.
• Total Rotational Motion (TRM): A difference in TRM (IR + ER) between shoulders of greater than 5° is related to a 2.5 times increase in injury risk.
Knowledge Check
A preseason functional ratio (eccentric ER to concentric IR) below 0.68 is associated with a 4.5-fold increased risk of in-season injury in adolescent swimmers.
Adult and Collegiate Swimmers (18--27 Years)¶
• Muscle Length: Tightness in the pectoralis minor (measured from the coracoid process to the 4th rib) is a significant predictor of pain.
• Horizontal Adduction: A cut point of less than 39° of horizontal adduction is associated with 3.6 times the risk of developing pain.
• Total Motion Threshold: TRM (sum of IR and ER) should not exceed 187° to maintain joint integrity.
3. Intervention Triggers by Ability Level¶
Elite and National Swimmers¶
• Structural Norms: High-resolution MRI shows that supraspinatus tendinopathy (70%) and subscapularis tendinopathy (73%) are nearly universal in elite asymptomatic swimmers. These findings should be viewed as normal adaptive changes; MRI should be reserved for athletes who fail 3+ months of conservative management.
• Baseline Torque: Elite athletes possess significantly higher baseline rotator torque (normalized to body weight) compared to university-level swimmers, which acts as a protective buffer against fatigue.
University and Club Swimmers¶
• Load Tolerance: This group experiences greater acute drops in shoulder force (15--21% drop in IR) and ER range of motion after a high-intensity session compared to elite athletes.
• Monitoring Trigger: Because club swimmers have a higher risk of pain than regional/national counterparts, they require more frequent monitoring of their training loads to avoid sudden spikes in volume.
Training Volume Cut-offs (General)¶
Screening should flag any adolescent or club swimmer exceeding 15 hours or 35 km of swimming per week, as 85% of supraspinatus tendinopathy cases can be predicted by these thresholds. For collegiate men, an injury rate of 1.56 per 1,000 athlete-exposures is the established norm for comparison.
Knowledge Check
Screening should flag any adolescent or club swimmer exceeding 15 hours or 35 km of swimming per week, as 85% of supraspinatus tendinopathy cases can be predicted by these thresholds.