## 5 Discussion
Abbreviations: D, dominant; ND, non-dominant; PESS, Physical Examination Shoulder Score; SCI, spinal cord injury; USPRS, Ultrasound Shoulder Pathology Rating Scale; NA, not applicable; \(\rho\) = Spearman’s rho. These data could be explained by the fact that manual wheelchair propulsion is an asymmetrical act, during which the magnitude of contribution of rotator cuff muscles while propelling is different from side to side; this difference may become more pronounced during challenging conditions [23; 26]. A previous study investigating asymmetries in bilateral scapular kinematics in a cohort of wheelchair athletes during activities of daily life (ADL) found limited associations to shoulder pain [27]. However, as the authors claimed, the ADL wheelchair propulsion can be considered a \"low risk\" activity in developing shoulder pain, probably due to the lower shoulder elevation required during ADL and the lower stresses to which rotator cuff muscles and tendons are subjected. In our study, the consequences of asymmetrical shoulder joint overload during challenging conditions are documented by the clinical (PESS) and ultrasonographic (USPRS) scores. The non-dominant shoulder had better scores than the dominant one, even if the differences were not statistically significant; this could be due to the small sample size. We speculate that the statistical correlation between non-dominant USPRS scores and WST performances could be consequent to the fact that during ADL, the non-dominant shoulder is probably less used by manual wheelchair users and therefore less damaged. Consequently, it could make a more significant contribution than the other shoulder during speed tasks. To the best of our knowledge, this is the first investigation of the relationship between shoulder pathology documented on ultrasound examination and WST performances, and no analogue studies were found in the literature search. The correlation between the non-dominant USPRS and the WST, both at baseline and after one year, seems to indicate that USPRS has evidence for external validity and may have a clinical impact in predicting the performance of wheelchair athletes in some specific tasks. Previous studies showed that chronic manual wheelchair uses severely impacts on shoulder joints [6; 22; 28; 29]. Our study confirms the existing literature concerning the high prevalence of rotator cuff pathology in manual wheelchair users [29; 30]: subacromion-deltoid bursa distension, supraspinatus tendinopathy, and supraspinatus ultrasound impingement signs were the most common shoulder ultrasound pathologic findings. Moreover, years of SCI seemed to correlate with the grade of rotator cuff tendon impairment of the dominant shoulder (USPRS score, \(p<0.005\)), with PESS and USPRS scores considerably high in the participants, despite their young age. These results agree with previous literature and confirm the importance of ultrasound evaluation in wheelchair athletes, because it can identify rotator cuff pathologies more frequently than common clinical tests [31]. A lack of correlation between the ultrasound shoulder scores (USPRS) and the corresponding findings of the clinical evaluation (PESS) was not surprising, because USPRS does not evaluate all the structures examined in the physical examination, and the presence of ultrasound pathology does not often correspond to the presence of pain symptoms [22; 31]. The skill tests (WST) were conducted under the same conditions in both sessions: the players sprinted on smooth terrain in a sports hall, using their defensive wheelchair chair. The presence of statistical correlation between the baseline results and those obtained after one year for both 20 m sprint (\(p<0.001\)) and the 30 m figure-of-eight sprint (\(p<0.05\)) proves that these results are reliable. However, no correlation was found between the performance tests and PESS. Probably, unlike the severity of shoulder pathology, the presence of low-intensity shoulder pain at rest or during physical testing does not influence the results of the WST.