ORIGINAL ARTICLE Adaptation of muscle activity in scapular dyskinesis test for collegiate baseball players Masaaki Tsuruike, PhD, ATC a, *, Todd S. Ellenbecker, DPT, SCS, OCS, CSCS b a Department of Kinesiology, San José State University, San José, CA, USA b Physiotherapy Associates Scottsdale Sports Clinic, Scottsdale, AZ, USA Background: The characteristics of scapular muscle activities in elevation and descent exercises have yet to be elucidated to assess scapular dyskinesis. The purpose of this study was to identify the adaptation of electromyograph (EMG) activities of the upper trapezius (UT), lower trapezius (LT), serratus anterior (SA), and anterior deltoid (AD) muscles with different weight loads in flexion (FLX) and abduction (ABD) in collegiate baseball players. Materials and methods: Twenty eight individuals, including 13 pitchers, were tested. Normalized EMG signals for the UT, LT, SA,AD muscle of the both the dominant (DOM) and nondominant (NON) side were blocked at every 1 second during each of the exercises. A 3-way repeated analysis of variance design was used to identify differences in the mean values between DOM and NON and between FLX and ABD for DOM. Results: The mean EMG value of the UT in the DOM was significantly less than that of the NON for all joint angles (P < .01), whereas the mean EMG value of the LT in the DOM was significantly greater than that of the NON (P < .01). In contrast, no difference in the SA EMG activity was determined between DOM and NON. However, the mean EMG value of SA in FLX was significantly greater than in ABD (P < .01). Conclusion: This study identified an apparent adaptation of scapular muscle activities in the currently advocated scapular dyskinesis test for healthy active overhead athletes who are vulnerable to shoulder pathologies. Level of evidence: Basic Science Study; Kinesiology © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. Keywords: Scapular dyskinesis test; EMG; Baseball players; Muscular adaptation; Bilateral comparison; Lower trapezius; Upper trapezius A dynamic test of scapular dyskinesis has been of interest to clinicians and researchers for the purposes of diagnosis and rehabilitation in the symptomatic shoulder. 2,4,5,7,8,10,12,15-18,20,23,25,28,30 Scapular dyskinesis is defined as altered scapular position in dynamic motion such as excessive internal rotation and ante- rior tilt of the scapula in the scapulohumeral rhythm (SHR). 7,9,12 The Institutional Review Board at San José State University (IRB Protocol #F1304025) approved this study. *Reprint requests: Masaaki Tsuruike, PhD,ATC, One Washington Square, San José, CA 95192-0054, USA. E-mail address: masaaki.tsuruike@sjsu.edu (M. Tsuruike). www.elsevier.com/locate/ymse ARTICLE IN PRESS 1058-2746/$ - see front matter © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. http://dx.doi.org/10.1016/j.jse.2016.03.004 J Shoulder Elbow Surg (2016) ■■, ■■–■■