Background: Asymmetric musculoskeletal adaptations, resulting from the type of sports, may lead to shoulder injuries due to altered shoulder mechanics and increased pressure on tissues. This study compared the scapulohumeral rhythm (SHR) ratio, flexibility, posterior capsule stiffness (PCS), and shoulder muscle strength between volleyball players as unilateral overhead athletes and swimmers as bilateral overhead athletes. Methods: Fifty-seven young overhead athletes, 30 volleyball players, and 27 swimmers participated in this study voluntarily. The SHR, PCS, and shoulder internal and external rotation ranges of motion (ROM) and strength in dominant and non-dominant limbs were measured using an inclinometer. Nicholas’s hand dynamometer was also used to evaluate the strength of internal and external shoulder rotators. Results: Findings indicated sport type had a significant effect on SHR ratio from 0˚ to 45˚ (p = 0.002), and from 0˚ to 135˚ (p = 0.002), external rotation (ER) ROM (p = 0.004), PCS (p = 0.002), internal (p = 0.004), and external (p = 0.002) rotator strength. Furthermore, the main effects of the dominance or non-dominance limb were significant for the scapular upward rotation (SUR) at 0˚ humeral elevation (p = 0.03) and external rotator strength (p = 0.01). On the other hand, the SHR ratio from 0˚ to 45˚ (p = 0.01) and from 0˚ to 90˚ (p = 0.01) was significantly less for the dominant limb than the non-dominant limb in volleyball players. Also, the pectoralis minor length was significantly shorter in the dominant limb compared to the non-dominant limb in volleyball players (p = 0.01). Furthermore, the dominant limb exhibited greater ER.ROM (p = 0.01) and external rotator strength (p = 0.02) compared to the non-dominant limb in volleyball players. Finally, swimmers had a significant difference in internal (p = 0.01) and external rotator strength (p = 0.01) between the dominant and non-dominant limbs. Conclusions: The effect of type sport on SUR at 0˚ and 135˚ humeral elevation, SHR from 0˚ to 45˚ and 135˚ hemeral elevation, internal rotators strength, PCS, and ER.ROM also the effect of dominance or non-dominance limb on SUR at 0˚ humeral elevation and external rotators strength can help physiotherapists and sports trainers to design prevention of injuries strategies in young overhead athletes.
