Abstract

Context: Knowing the possible association between the isometric strength of the shoulder rotators, scapular muscles, and the Ybalance test upper quarter (YBT-UQ) performance could help identify which indicators of shoulder stability should be considered in this field test. This study aimed to determine whether the isometric strength of the shoulder rotators and scapular muscles is associated with the YBT-UQ performance of the dominant upper limb in amateur volleyball players. Design: Cross-sectional study. Methods: A convenience sample of 22 male and 18 female volleyball players (>= 12 h of training/week) between 18 and 26 years of age. The isometric strength of the middle trapezius, lower trapezius, serratus anterior, internal, and external rotator muscles was assessed with a handheld dynamometer. Participants performed the YBT-UQ in the superolateral, medial, and inferolateral directions. The absolute isometric peak force (in Newtons) was normalized to body weight (in Newtons per kilogram) for each muscle test. For each YBT-UQ direction, the distance (in centimeters) was normalized for upper limb length (in percentage). A backward multiple linear regression analysis was used to determine the associations between variables. Results: The analysis revealed that the isometric strength of the lower trapezius (beta = 26.82; 95% confidence interval, 21.24- 32.40) is associated with inferolateral YBT-UQ performance (adjusted R2 =.706; P<.001). This factor explains 70% of the variability of the YBT-UQ in the inferolateral direction. Conclusions: Lower trapezius isometric strength is associated with inferolateral YBT-UQ performance of the dominant upper limb in amateur volleyball players. These findings could help in the development of more specific training programs and rehabilitation goals according to the performance of the athletes in the test.