Associations Between Pelvis, Trunk, and Shoulder Girdle Muscle Activity; Age; and Scores During the Closed Kinetic Chain Upper Extremity Stability Test in Baseball Pitchers

OBJECTIVE: To evaluate associations between muscle activity, age, and scores on the Closed Kinetic Chain Upper Extremity Stability Test (CKCUEST). DESIGN: Quasi-experimental. METHODS: Pelvic, trunk, and shoulder girdle surface electromyography (sEMG) and kinematic data were measured in 21 high school and college male baseball pitchers (17.4 ± 2.0 years, 184.4 ± 5.7 cm, 78.4 ± 14.2 kg) while they performed the CKCUEST. Mean sEMG data were computed while in sole support on the throwing-arm side (TS) as the glove-arm side (GS) was horizontally translating. Correlations and local regressions were used to assess associations and general patterns between mean sEMG data, age, and scores. RESULTS: TS serratus anterior, TS external oblique, GS serratus anterior, and TS gluteus medius had the highest mean sEMG data. Low-to-high significant correlations were found between proximal muscle groups. Correlations with the highest magnitudes in descending order were TS external oblique and TS gluteus maximus, TS external oblique and TS serratus anterior, and GS external oblique and TS gluteus medius. Small significant associations were observed between other muscle groups and age; there were no associations between muscle activity and test performance. CONCLUSION: Associations were observed between mean muscle activity among muscle groups and age but not test outcome. J Orthop Sports Phys Ther 2024;2(4):1-9. Epub 7 June 2024. doi:10.2519/jospt.2024.1023