Shoulder strength and scapular position in swimmers

Background and Aims Shoulder pain is common in swimmers, resulting in many young athletes leaving the sport. Despite the investigation of factors associated with shoulder pain in swimming, no consensus exists regarding risk factors for the development of swimmers' shoulder pain. Clinicians commonly assess shoulder strength and scapular position, which have been postulated as factors contributing to swimmers' shoulder pain. However, normative data is lacking, making it difficult to identify optimal parameters for shoulder strength or scapular position. Indeed, until normal parameters are defined using reliable and valid assessment tools and procedures, the relevance and association of these factors with shoulder pain in swimmers, remains uncertain. The overarching aim of this research was to investigate the relationship (association and predictive value) of shoulder strength and scapular upward rotation (UR) with the development of shoulder pain in young swimmers. To complete this investigation, four concomitant studies were undertaken. The first study aimed to examine the reliability of measurements taken with two clinically useful tools, the hand-held dynamometer (HHD) and the inclinometer, in elevated shoulder positions (90¬¨‚àû and 140¬¨‚àû shoulder abduction), that are relevant to swimming. The second and third studies aimed to establish normative data for shoulder strength in pain-free swimmers (internal rotation [IR], external rotation [ER], flexion [FL] and extension [EX]) and scapular UR in the functional, elevated shoulder positions of 90¬¨‚àû and 140¬¨‚àû shoulder abduction. The fourth study aimed to investigate prospectively whether shoulder strength or scapular UR had any association with, or predictive value for, the development of shoulder pain in young swimmers. Methods and Results A protocol for the measurement of isometric shoulder IR, ER, FL and EX strength using a HHD in elevated shoulder positions was tested for reliability in supine, prone and sitting positions. Good to excellent intra-rater reliability was found for all shoulder strength tests (ICC 0.87-0.99) which was not affected by body position. The minimal detectable change (MDC) percentage was <16% for every test and ‚Äöv¢¬ß11% for all tests performed in supine (Chapter 3). The reliability for scapular UR measurements in 90¬¨‚àû and 140¬¨‚àû of shoulder abduction, using an inclinometer was also established (ICC 0.62-0.86). Standard error of measurement (SEM) values ranged from 1.2¬¨‚àû to 2.7¬¨‚àû (Appendix D). Following the establishment of a reliable protocol, shoulder strength and scapular UR angle measurements were performed on 85 pain-free swimmers (mean age 15.5; range 14-20 years[yrs]) who swam a minimum of six hours per week. Training and shoulder pain history were recorded via a questionnaire and established that 32% of swimmers had a history of shoulder pain that caused the swimmer to miss or modify two or more swim training sessions. Strength measurements normalised to body weight (BW) and strength ratios for IR:ER and FL:EX were calculated to establish normative data for the group (Chapter 4). Relative strength differences between males and females were found (p<0.002); however, there were no differences in shoulder strength ratios. Relative shoulder strength was the same for the dominant and non-dominant arms (except for shoulder EX in males), and for the swimmers with and without a history of shoulder pain for all strength tests. Scapular UR angle measurements were found to be highly variable between swimmers, with a large range of values recorded (Chapter 5). The mean (¬¨¬±SD; range) scapular UR angle recorded at 90¬¨‚àû and 140¬¨‚àû shoulder abduction was 30¬¨‚àû (¬¨¬±8.7; 10-50¬¨‚àû) and 52¬¨‚àû (¬¨¬±7.8; 30-70¬¨‚àû) respectively. However, side-to-side symmetry for scapular UR was found within swimmers and was not affected by a history of shoulder pain or arm dominance. This was confirmed when a sub-group of swimmers (n=17) who reported a history of unilateral shoulder pain were investigated using paired t-tests. No differences in scapular UR angles were found between shoulders with and without a history of pain (p‚Äöv¢‚Ä¢0.11). To explore any relationship between shoulder strength and scapular UR angle and the development of shoulder pain, a longitudinal study was conducted (Chapter 6). Swimmers were followed up via a questionnaire emailed initially at a minimum of nine months and again up to 24 months (for non-responders and if pain was not reported on the initial questionnaire) after testing. The questionnaire aimed to establish if significant shoulder pain had been experienced by the swimmer in the 24 months after testing and if so, in which shoulder. Analysis of the strength data from 37 (47%) swimmers who responded (27 shoulders with reported pain and 47 without pain) was performed using Mann Whitney U tests and receiver operating curves (ROC). A relationship was confirmed between low shoulder EX strength in males (and consequently a higher FL:EX strength ratio) and the development of shoulder pain (p=0.04). Furthermore, the predictive value of shoulder EX strength was fair (0.72; p=0.03) for males, with a cut off value for EX strength calculated at below 13.5% BW. There were no differences between the swimmers who development shoulder pain and those who did not for shoulder rotation strength, scapular UR (Appendix J), swim training hours, age or shoulder pain history. Conclusions This body of work has established a reliable testing protocol and normative strength values for shoulder FL, EX, IR, ER, shoulder strength ratios and scapular UR values, which are specific to a young swimming population. The results provide a reference point for clinicians and indicate that the unaffected shoulder is valid for comparison in the assessment of shoulder strength and scapular UR, regardless of a history of shoulder pain. The results from the longitudinal study support functional shoulder strength testing of young swimmers, finding that reduced shoulder EX strength is a potential risk factor for the development of shoulder pain in young male swimmers. Low shoulder EX strength may help identify swimmers at risk of developing shoulder pain, specifically, males with shoulder EX strength below 13.5% BW.