## 4 Discussion
The reduction in the deltoid muscle contraction and the increase in the activity of the teres minor and anterior serratus obtained at the end of the treatment proposed (T1) could counteract the upward migration of the humeral head and increase joint stability. This contributes to improving the shoulder biomechanics and dynamic stabilization of the humerus in the glenoid, which is very important for the prevention and treatment of shoulder rotator cuff impingement syndrome [33]. Ergonomics plays an important role in minimizing the frequency and strength needed to complete upper limb activities and to avoid extreme or potentially harmful positions in alljoints during wheelchair propulsion. Numerous studies have reported propulsion kinetics and kinematics and have suggested several ways to improve propulsion efficiency [7; 37]. For this reason, wheelchair athletes were trained to improve efficiency through long and fluid propulsion strokes [6; 14]. To quantify the smoothness of movement, we used the APR, a mathematical measure of the relationship between the area and the perimeter of a regular geometric figure. The APR is maximum for a circle. Generally, for the same perimeter of a regular polygon, the greater the number of sides, the greater the area. As a result of analyzing the most common propulsion model, the semicircle is the recommended model because it offers some biomechanical advantages compared to the other model and therefore could reduce the risk of shoulder injuries [8]. It also has the highest APR. Thus, at T1, the increase in APR indicates a propulsion model with a more regular propulsion stroke, with no sudden changes of direction and no extra hand movement. The optimization of the thrust arc can determine the best balance between peak force and task repetition. To estimate the efficiency, the acceleration of a single stroke was used. Within each propulsion stroke, significant braking moments and power loss are generated. If F = ma, and m is a constant because a standard system was used, a higher acceleration at T1 means that the resultant of the force applied to the wheel is higher, because the wasted vector of force is less, and the stroke pattern is more efficient. This is consistent with the results of a study by [PERSON] [37], who found that the semicircular pattern (under-rim stroke) resulted in smaller negative deflection in axle moment. Considering the symmetry ratio (sym), an average score of less than 45% at T0 is indicative of a preference for the non-dominant hand during wheelchair acceleration, which can contribute to the development of shoulder injuries. At T1, a sym of between 45 and 55% is the result of better coordination during the stroke cycle. The significant improvements in APR, acceleration, and sym showed that athletes had changed their propulsion technique, and had a more fluid, efficient, and symmetrical push mode. Therefore, our results showed that shoulder injury prevention might be accomplished by performing exercises that improve flexibility and strength, and wheelchair athletes can achieve the goal of improving the range of shoulder movements to prevent injury [6; 14; 33; 34]. The present study is not free from limitations. Firstly, the small sample size and the lack of a control group could affect the results and the generalizability of the results, with a potential overestimation of the outcomes. Secondly, sEMG measurements could present artifacts due to muscle crosstalk, although we tried to minimize this by considering and carefully selecting the appropriate electrode size, inter-electrode distance, and locations for electrode placement. Study participants were recruited from a local adapted sports team. Moreover, in this study we did not consider ultrasound as an examination tool [38] for muscle and tendons. Lastly, the small team size and inclusion-exclusion criteria limited the number of eligible participants. Further studies are needed to improve the generalizability of the results, including a larger sample size and a control group.