## 2 Materials and Methods  
This was an observational prospective study on a cohort of wheelchair rugby athletes. Nineteen quadriplegic male members of the Italian National Wheelchair Rugby Team with a history of traumatic spinal cord injury (SCI) were enrolled. The athletes were included in the study if they had a history of at least five years of SCI that limited mobility of both arms, and if they used a manual wheelchair as the primary means of mobility during daily life and a defensive wheelchair rugby chair during sport activities. The exclusion criterion was a history of shoulder joint traumatic injuries such as fractures or traumatic rotator cuff muscles tears. This study followed all the recommendations for research in human beings and all participants signed an informed consent form before the assessments, in accordance with procedures of the Institutional Review Board. Age, level and age of SCI, number of daily transfers, body mass index (BMI), and defensive wheelchair rugby chair weight were measured. Moreover, the International Wheelchair Rugby Federation Classification (IWRFC) score for each participant was registered. IWRFC classifies players in seven groups depending on their level of disability, ranging from 0.5 (most impaired) to 3.5 (least impaired) [20]. Each athlete underwent a neurological physical examination to determine the motor level, the sensory level, and the completeness of SCI, and the American Spinal Injury Association Impairment Scale (AIS) score was determined accordingly. AIS classification identifies key muscles and sensory points corresponding to different myotomes and dermatomes for each side of the body. The motor score is based on the strength of 10 pairs of key muscles in the upper and lower limbs; the sensory score is based on pin-prick and light touch scores in each of the key sensory dermatomes [21]. Shoulder examination was also performed, and the Physical Examination Shoulder Score (PESS) of both the dominant and non-dominant shoulder was calculated. PESS is a shoulder evaluation scale that was firstly described and validated by [PERSON] et al. [22]. It consists of 11 physical examination maneuvers for rotator cuff disease and shoulder pain that are graded 0 (no pain), 1 (equivvocal for pain), or 2 (pain present). PESS maneuvers consist of palpation over the bicipital groove/bicep tendon; palpation over the greater tuberosity/supraspinatus tendon; palpation over the acromioclavicular joint; Neer sign; Hawkins-Kennedy sign; shoulder range of motion; [PERSON]'s test; resisted external rotation; resisted internal rotation; and O'Brien test for the labrum, O'Brien test for the acromioclavicular joint. PESS can range from 0 (best score) to 22 (worst score). A B-mode sonographic evaluation of both shoulders was performed by a radiologist with a SonoSite M-Turbo(r) machine (Fujifilm Sonosite Europe, Amsterdam, 1114 AB, Netherlands) and a 6-13 MHz linear transducer. The examiner (a certified medical sonographer) was blind to the results of the physical examination. Subjects were evaluated in a sitting position and the examination was conducted according to the Musculoskeletal Ultrasound Technical Guidelines of the European Society of Musculoskeletal Radiology [23]. The Ultrasound Shoulder Pathology Rating Scale (USPRS), developed and validated by [PERSON] et al. [22], was used to quantify the severity of shoulder pathology of each athlete. This scale considers 5 pathologic findings: greater tuberosity cortical surface irregularity; supraspinatus tendinopathy; bicipital tendinopathy; supraspinatus impingement; and subscapularis/biceps/coracoid impingement. The USPRS score is determined by the sum of the 5 scores, with a maximum total score of 20 (worst score), and the shoulder pathology depends on the presence and the severity of these findings. The USPRS results of the dominant and non-dominant shoulder were recorded. The WSTs were conducted in the sports hall at the beginning (within one day after the shoulder examination) and the end of the study (after one year).