Muscle Activity Ratios of Scapular Stabilizers During Closed Kinetic Chain Exercises in Healthy Shoulders: A Systematic Review

Context: Selective strengthening of scapular stabilizers is one of the emphases of the recent literature. Closed kinetic chain (CKC) exercises are used extensively in shoulder rehabilitation. However, a limited number of studies have reported scapular muscle ratios during CKC exercises. Objectives: To determine the CKC exercises producing the optimal ratios of the scapular stabilizer muscles in healthy shoulders. Evidence Acquisition: A systematic search within PubMed, Embase, CINAHL Plus, and SPORTDiscus with Full Text and ULAKBIM National Medical Database was performed up to January 2018. Studies were selected according to the predetermined criteria. If the pooled mean ratios (upper trapezius [UT]/middle trapezius [MT], UT/lower trapezius [LT], and UT/serratus anterior [SA]), which were calculated from the percentage of maximum voluntary contractions of muscles, were <0.60, these exercises were considered as ideal for higher activation of the MT, LT, and SA than the UT. Evidence Synthesis: The search identified 1284 studies, and 29 observational studies were included for review. Seventy-nine CKC exercises were determined. Four exercises for the MT, 9 for the LT, and 59 for the SA were identified from the articles as being optimal exercises to activate the specified muscle more than the UT. Conclusions: This review identified optimal CKC exercises that provide good ratios between the MT, LT, and SA with the UT, Most exercises have optimal UT/SA ratios, but some exercises performed on unstable surfaces may lead to excessive activation of the UT relative to the SA. For the UT/MT, the isometric low row, inferior glide, and half supine pull-up with slings are the ideal exercises. Isometric one-hand knee push-up variations seem to be the best choice for the UT/LT. The results suggest that many CKC exercises may be utilized to enhance scapular muscle balance when rehabilitating shoulder pathology.