Background: Scapular dyskinesis (SD) is closely related to imbalance of the rotator cuff (RC) muscles. However, previous studies have only focused on isometric strength. To our knowledge, there has been no study examining potential differences in concentric and eccentric strength and functional strength ratio (FSR) of the RC muscles based on functional parameters related to throwing in with or without SD. Objects: This study aimed to determine whether there was a difference in the RC muscle strength and FSR between the dominant shoulder with SD and the non-dominant shoulder without SD in adolescent baseball players. Methods: Forty adolescent baseball players participated and classified types of SD based on movement patterns using the SD test by two examiners. The isokinetic concentric and eccentric peak torque of the internal rotation (IR) and external rotation (ER) were measured and quantified as peak torque to body weight (PT/BW). Also, the FSR was obtained by calculating the strength ratios of eccentric IR to concentric ER (IRecc/ERcon) and eccentric ER to concentric IR (ERecc/IRcon), respectively. Results: There was a significant decrease in the IR and ER PT/BW in the dominant shoulder with SD compared to the non-dominant shoulder without SD (p < 0.05), regardless of contraction types. However, no significant difference was observed in the FSR in both IRecc/ERcon and ERecc/IRcon ratios. Conclusion: The findings indicate that the isokinetic concentric and eccentric PT/BW of the IR and ER muscles were significantly lower in the dominant shoulder with SD than in the nonthrowing shoulder without SD. Therefore, when establishing a strategy for addressing RC muscle weakness in adolescent baseball players with SD, it is essential to consider an approach that accounts for scapular kinematic recovery.

Background: Scapular dyskinesis is characterized by altered scapular position and motion. Specifically, excess activation of the Upper trapezius (UT) combined with decreased Lower trapezius (LT) and Serratus anterior (SA) have been observed. The Standard push-up plus exercise (SPP) is considered as a therapeutic exercise for increasing SA activity and maintaining the scapular kinematics. In addition, Using the Sling surface can lead to higher muscle activity. However, the advantage of an unstable surface has been uncertatin. Objects: To compare the activation of the UT, LT, and lower serratus anterior (LSA) muscles during various push-up plus exercises with and without sling in subjects with scapular dyskinesis. Methods: Total 18 male subjects with scapular dyskinesis were recruited. The UT, LT, and LSA electromyographic activities and the UT/LSA and UT/LT EMG activity ratios were measured during three push-up plus exercises with and without sling. Two-way repeated of analysis of variance was used to determine the statistical significance. Results: The UT activity was significantly lower in all postures without sling than that with sling. In addition, the LSA activity was significantly greater without than with sling, and significantly large in SPP, Low back supported push-up plus (LSPP), and Quadruped push-up plus. Additionally, the UT/LSA and UT/LT activity ratios were lower in SPP and LSPP without sling than with the other four push-up plus exercises. Conclusion: The push-up plus without sling were considered to decrease UT and increase LSA activity compared with exercises with sling. Furthermore, SPP without sling seems to be a more effective exercise for increasing LSA activity and lowering the UT/LSA and UT/LT activity ratios in scapular dyskinesis subjects.