Adaptation Characteristics in the Range of Motion of the Shoulder Among Young Male Volleyball Players

Background/Objectives: Repeated spiking and serving movements in volleyball can lead to alterations in shoulder range of motion among athletes, potentially increasing the risk of shoulder instability and injury. Hence, assessing and understanding the shoulder range of motion of volleyball players is a critical concern. Therefore, this study aimed to understand and evaluate the bilateral shoulder joint range of motion (ROM) in high-school male volleyball athletes and to discover the adaptation characteristics. Methods: Forty high-school male volleyball athletes participated in this study. Shoulder ROM measurements were taken via video with an iPhone 12 Pro Max, and we analyzed the ROM data using Kinovea software (Version 0.9.5) for both the dominant and non-dominant side. The shoulder ROM measurements included shoulder hyper-extension (SE), flexion (SF), internal rotation (IR), external rotation (ER), horizontal adduction (Sadd), and horizontal abduction (Sabd). After taking shoulder ROM measurements, the total rotational range of motion (TROM) was calculated based on the participants' shoulder internal rotation and external rotation data, and we calculated the incidence of glenohumeral internal rotation deficiency (GIRD) among participants. Paired samples t-tests were used to analyze shoulder ROM differences between the dominant and non-dominant side. Results: The dominant side of the shoulder showed significantly lower internal rotation (dominant side: 42.17 ± 11.23°; non-dominant side: 52.14 ± 10.46°; p = 0.000) and total rotational ROM (dominant side: 137.11 ± 13.09°; non-dominant side: 141.96 ± 13.22°; p = 0.021) compared to the non-dominant side. Conversely, the dominant side of the shoulder exhibited significantly greater external rotation (dominant side: 94.96 ± 10.02°; non-dominant side: 89.83 ± 7.84°; p = 0.001) and shoulder horizontal adduction (dominant side: 44.87 ± 8.10°; non-dominant side: 39.60 ± 7.24°; p = 0.000) than the non-dominant side. No significant differences were found in other measured parameters. The incidence of glenohumeral internal rotation deficiency (GIRD) among all subjects was 37.5%. Conclusions: High-school male volleyball athletes in this study exhibited tightness in the posterior shoulder of their dominant side, indicating specific adaptations in shoulder ROM and a considerable prevalence of GIRD, observed in approximately one-quarter of the athletes. In conclusion, these data suggest that stretching and eccentric muscle training focusing on the posterior shoulder have potential value in mitigating these adaptations and reducing the risk of shoulder injuries.