Lake Erie College of Osteopathic Medicine Saint Petersburg, Florida, United States
Background and Hypothesis: Previous studies have demonstrated that the significant amount of repetition and stress load on the shoulder throughout the entire overhead throwing motion in baseball can lead to shoulder injuries. Restricted hamstring range of motion (ROM) may place additional stress on the throwing shoulder and increase the risk of injury. Current literature emphasizes the effects of hamstring inflexibility and throwing shoulder total ROM in adult baseball players. We aim to identify the association between the contralateral hamstring-popliteal angle and throwing shoulder total ROM in high school baseball players, specifically.
Methods: 14 high school varsity baseball players (ages 14 to 18 years old) volunteered for this study. All the athletes played 5 times a week and played different positions. The study was completed at local baseball field where the high school team practiced under the supervision of a board-certified physician. Inclusion criteria included high school aged males on the varsity baseball team. Exclusion criteria included current leg or arm injuries, as documented with a pre-screening questionnaire. Bilateral hamstring and throwing shoulder total ROMs were measured using a goniometer by the same examiner. Three examiners determined maximum ROM by joint end feel for each measurement to ensure quality control. Contralateral hamstring flexibility was measured using the popliteal angle test. These measurements were compared to the throwing shoulder total ROM to determine the presence of an association. The relationship between the contralateral hamstring flexibility and throwing shoulder total ROM was determined using a linear regression analysis.
Results: Baseball players with higher popliteal angles were found to have higher throwing shoulder total range of motion, which represents the overcompensation that occurs with hamstring inflexibility. The correlation coefficient, r, of this study was + 0.3928, indicating a moderate positive linear relationship. The stride position is the component for proper positioning of the trunk and lower extremity in the transfer of energy to the throwing shoulder by increasing the distance and time that the trunk can rotate. A short stride would decrease force development by reducing trunk rotation potential. A key factor limiting stride length is soft tissue flexibility restrictions in the lead leg hamstring muscle group. We conclude that higher contralateral hamstring-popliteal angles may cause a compensatory increase in throwing shoulder total ROM, which may increase the risk for shoulder injuries due to excessive stress and ROM.
Conclusion: Overhead throwing athletes with limited hamstring flexibility should be counseled appropriately regarding their risk for shoulder injury. Baseball players should stretch and prepare their bodies to throw to reduce the compensatory mechanisms that may occur from hamstring inflexibility. Future applications of this study findings include developing a muscle energy and spencer technique protocol that improves hamstring flexibility and shoulder TROM, respectively to reduce the risk of throwing shoulder injuries. Additional research with a larger sample size is encouraged to further establish the association between contralateral hamstring-popliteal angles and throwing shoulder total ROM. We highlight the role hamstring inflexibility may play in shoulder injury development in adolescent baseball players.
Acknowledgement of Research Study Sponsors and IRB: Thank you to the Lakewood Ranch baseball team for participating in this study.
