Optimal activation ratio of the scapular muscles in closed kinetic chain shoulder exercises: A systematic review

Abstract

BACKGROUND: Muscle synergies contribute to scapular position during arm movement. The trapezius and serratus anterior (SA) muscles are the main stabilizers and are therefore the main target muscles of therapeutic exercises. OBJECTIVE: To systematically review the current literature investigating the optimal activation ratio of the scapular muscles during a range of closed kinetic chain exercises. METHODS: A systematic review search was conducted to identify studies reporting shoulder electromyography (EMG) activity during rehabilitation exercises in healthy participants. The search was conducted in PubMed, Cochrane Library, MEDLINE, CINAHL, Scopus, SPORTDiscus, and ScienceDirect. The included studies reported closed kinetic chain exercises and the muscle activity as a percentage of maximum voluntary isometric contraction (%MVIC) or muscle ratios of the lower trapezius (LT), middle trapezius (MT), and SA with respect to the upper trapezius (UT). Muscle ratios were classified as optimal if they were equal to or lower than 0.6, and the adapted Newcastle-Ottawa Scale (NOS) was used to evaluate the methodological quality of the selected studies. RESULTS: Twenty-nine studies were included in this review; 7 main exercises and 30 variations of these were reported. The average electromyographic activity of the concentric and eccentric phase was considered. Half Push Up, Push Up Plus, and Scap Protraction exercises showed optimal SA activity (UT/SA < 0.6), while Press Up, Half Push Up, and One Hand Plank exercises showed optimal LT activity (UT/LT < 0.6). According to the NOS, 15 studies were classified as moderate methodological quality. CONCLUSIONS: The exercises in higher positions (e.g. exercises with the trunk closest to the vertical line) or unstable surfaces tend to favor UT activity over the MT, LT and SA. The exercises including scapular retraction showed optimal UT/MT and UT/LT ratios, while those including scapular protraction showed optimal UT/SA ratios. This will assist therapists in the correct selection of exercises for shoulder rehabilitation.

Electromyographic analysis of the serratus anterior and upper trapezius in closed kinetic chain exercises performed on different unstable support surfaces: a systematic review and meta-analysis

“…The present investigation had limitations: (i) this report was based only on the EMG activity normalized by MVIC and did not consider the UT/SA ratio as a valid outcome measure for inter-subject comparisons. This measurement has been widely reported as the outcome that allows making comparisons between individuals and exercises, as well as this allows evaluating and analyzing the intra and inter-muscular balance ( Ludewig et al, 2004 ; Berckmans et al, 2021 ); (ii) as reported by other reviews ( Kang et al, 2019 ; Mendez-Rebolledo et al, 2021 ) most of the included studies did not present a priori a sample size or the statistical power of the analyzes, and they recruited participants healthy and asymptomatic, which make difficult to fully extrapolate the results of this research to populations with shoulder musculoskeletal dysfunctions; (iii) 93,3% the included studies showed a moderate methodological quality, mainly due internal validity aspects; and (iv) the present investigation was not able to carry out a meta-analysis for the push-up plus exercise, considering that add scapular protraction may increment the myoelectrical activity of the SA, involved directly in this movement. Finally, and according to GRADE, the certainty of evidence ranged from “very low” to “low” for the outcomes, harming the confidence in the presented estimates.…”

“…An author (OC) completed the extraction of data from selected studies. Due to the heterogeneity of the nomenclature and design of the exercises reported in the literature, these were categorized according to previously described criteria ( Mendez-Rebolledo et al, 2021 ; Cappato de Araújo et al, 2021 ). A second author (MV) checked the accuracy and consistency of all entries and made relevant clarifications when necessary.…”

“…In this context, there is evidence that suspension mechanisms and the therapeutic ball could generate a greater neuromuscular recruitment demand compared to other support surfaces such as BOSU or floor ( Lehman, Hoda & Oliver, 2005 ; Imai et al, 2010 ; Behm & Colado, 2012 ; Czaprowski et al, 2014 ; Borreani et al, 2015a ; Youdas et al, 2020b ). However, the comparative analyzes observed in previous reviews ( Kang et al, 2019 ; Cappato de Araújo et al, 2021 ) have grouped in a single data pool different types of unstable support surfaces—BOSU, therapeutic ball, suspension equipment, among others—without considering the possible and potential differences in neuromuscular demand induced by the individual analysis of each unstable support surface ( Mendez-Rebolledo et al, 2021 ). In this context, to our knowledge, there is no quantitative analysis of the evidence that groups the data according to these differences.…”

Shoulder and Scapular Muscle Activity During Low and High Plank Variations With Different Body-Weight-Bearing Statuses

“…There are previous reports on 4-point and 3-pod variations of the plank exercise (11,22,25,34). In previous studies, higher UT, MT, LT, SA, and IS muscle activation levels have been observed in the 3-pod plank and push-up variations compared with the 4-point exercises (11,21,25,32).…”

No pain, no gain? (Re)opening up research in 2021

“…These, from now on free to read, 65 reviews provide us a meaningful insight in the current 66 evidence of MSD-related therapies. The first study, car-67 ried out by Mendez-Rebolledo and colleagues [1]…”