The relationship between scapular dyskinesis and rotator cuff strength in adolescent baseball players

Article type: Research Article

Authors: Yu, Il-Young^a | Ma, Rui^b | Kim, Tae-Gyu^{a; *}

Affiliations: [a] Department of Major of Marine-Sports, Division of Smart Healthcare, Pukyong National University, Busan, Korea | [b] Department of Physical Education, Henan Agricultural University, Zhengzhou, China

Correspondence: [*] Corresponding author: Tae-Gyu Kim, Department of Major of Marine-Sports, Division of Smart Healthcare, Pukyong National University, 45, Yongso-ro, Nam-gu, Busan 48513, Korea. Tel.: +82 51 629 5007; E-mail: Ktk7718@gmail.com.

Abstract: BACKGROUND: In overhead athletes, including adolescent baseball players, scapular dyskinesis is linked to rotator cuff muscle weakness. This relationship exists because the scapula provides a stable platform and maintains the optimal length – tension relationship essential for maximal rotator cuff muscle force. While the link between scapular dyskinesis and the isometric strength of the rotator cuff has been studied, the connection with dynamic strength, particularly isokinetic concentric and eccentric strength, and their effects on functional strength ratios (agonist concentric strength to antagonist eccentric strength ratio), remain less clear. OBJECTIVES: This study aimed to explore the association between scapular dyskinesis and the isokinetic concentric and eccentric strength of the rotator cuff muscles, functional strength ratios, and shoulder function, as well as to determine the differences in these parameters between the dominant shoulder with scapular dyskinesis and the non-dominant shoulder without dyskinesis in adolescent baseball players. METHODS: This study included 50 adolescent baseball players with scapular dyskinesis. Measurements included scapular movement patterns in the scapular dyskinesis test, scapular dyskinesis scores, isokinetic concentric and eccentric internal and external rotation torques (expressed as peak torque/body weight, %), functional strength ratios, and shoulder function. Correlations between scapular dyskinesis scores and various strength and functional measurements were analyzed, as well as differences between the dominant and non-dominant shoulders using the paired t-test. RESULTS: Internal and external rotation torques were reduced on the scapular dyskinesis side across all types of contractions. A weak negative correlation was observed between the scapular dyskinesis score and eccentric internal rotation torque, with no significant correlations seen for the other variables. A moderate negative correlation was found between concentric internal rotation torque and the eccentric external rotation/concentric internal rotation ratio. Additionally, concentric and eccentric external rotation torques showed a weak negative and a positive correlation with the eccentric internal rotation/concentric external rotation ratio, respectively. CONCLUSIONS: Reduced isokinetic strength was noted on the scapular dyskinesis side, correlating particularly with eccentric internal rotation torque. This study highlights the relationship between rotator cuff muscle strength and functional strength ratios, suggesting the need for targeted strategies to restore balance between scapular positioning and rotator cuff strength.

Keywords: Scapular dyskinesis, rotator cuff muscle strength, functional strength ratio, adolescent baseball players

DOI: 10.3233/IES-240018

Journal: Isokinetics and Exercise Science, vol. Pre-press, no. Pre-press, pp. 1-9, 2024