## 1 Introduction  
Wheelchair rugby is a popular Paralypic team discipline available to individuals with different disabilities that affect arms and legs; most athletes present a cervical spinal cord injury (SCI) with full or partial paralysis [1].  
Wheelchair rugby is considered a sport with high risk of injury, and athletes are more prone to injuries of the upper extremities [2, 3, 4]: manual wheelchair use may determine shoulder joint overload, and repetitive microtraumas can cause rotator cuff tendinopathy and muscle tears [5, 6]. The presence of chronic shoulder pathologies often causes symptoms such as pain, stiffness, weakness, and joint instability, hence it could also impact the wheelchair athletes' propulsion ability during sport activities [2, 7, 8].  
Shoulder ultrasound represents an extremely sensitive imaging tool to investigate the presence of shoulder joint and rotator cuff disease, even in manual wheelchair users. It represents a non-invasive, cost-effective, rapid, easily accessible real-time exam, and can be employed on the sport field during training and competitions. However, the inconvenience is that it does not provide any direct information about the wheelchair performance of athletes [9].  
In order to assess athletic performance, many wheelchair skills tests (WSTs) have been employed [10; 11; 12]. Among them, team coaches seem to prefer the field-based test for their ease of execution and reliability in mimicking game situations [13]. During these tests, participants must perform motor skills required in wheelchair sport activities such as sprints, changes of direction, obstacle avoidance, braking, etc. Together with information about the athlete's performance, these tests can provide several biomechanical parameters that could be affected during wheelchair propelling (e.g., the change in human body center of gravity position, which is connected to the different rolling resistance between initial and final stages of the propulsion phase, and between front and rear wheels) [14]. The analysis of these parameters provides important information about the musculature involved during wheelchair propulsion, because acceleration, braking, turning, and ball handling are hardly dependent on trunk stability and upper extremity strength. These characteristics are often compromised in athletes with SCI, who compensate the impairment with alternative postural strategies and the activation of compensatory muscles [15; 16; 17].  
The results of these tests give some quantifiable information related to the propulsion ability of the athlete [10; 11; 12; 13; 18], but they do not provide any clue about the factors that affect wheelchair performance.  
Many studies have shown the negative influence of manual wheelchair use on the shoulder joint and rotator cuff muscles [5; 19], but, to the best of our knowledge, the relationship between shoulder pathology and wheelchair performance has never been explored.  
Therefore, the purpose of this study was to conduct a clinical and ultrasonographic evaluation of dominant and non-dominant shoulder conditions of a cohort of wheelchair rugby players, and their correlation with the results of two wheelchair performance tests evaluating the propulsion speed and the wheelchair mobility skill. The hypothesis was that the worse the results of the WST, the more the shoulder damage would have been.