Rehabilitation Exercises for Dysfunction of the Scapula: Exploration of Muscle Activity Using Fine-Wire EMG

Abstract

Background: Scapular muscle activity during shoulder exercises has been explored with surface electromyography (EMG). However, knowledge about the activity of deeper-layer scapular muscles is still limited. Purpose: To investigate EMG activation of the deeper-layer scapular stabilizers (levator scapulae [LS], rhomboid major [RM], pectoralis minor [Pm] muscles) together with superficial muscle activity (upper [UT], middle [MT], and lower trapezius [LT] and serratus anterior [SA]) during 4 exercises often used for training scapular function. Based on the amplitude EMG of the deeper-layer muscles, scapular muscle activation ratios for the 4 exercises were calculated, hereby providing knowledge of the optimal muscle balance. Study Design: Descriptive laboratory study. Methods: A total of 26 healthy participants performed 4 shoulder exercises (side-lying external rotation [ER], side-lying forward flexion, prone horizontal abduction with ER, and prone extension) while simultaneously measuring scapular muscle activity. Intramuscular electrodes were used for the deeper layer, in contrast to surface electrodes for the superficial muscles. All data were normalized to percentage of maximal voluntary isometric contraction (%MVIC), and the activation ratios (the muscle activity of the deeper layer relative to the other muscles) were calculated. A 1-way analysis of variance with Bonferroni correction was applied for statistical analysis. Results: Moderate activity was found in all exercises for the LS and RM (25%-45% MVIC). The Pm resulted in low activity during both side-lying exercises (13%-18% MVIC). Ratios involving LS or RM showed values >1 for all exercises (1.28-12.41) except for LS/MT, LS/LT, and LS/RM (0.85-0.98) during side-lying ER, and LS/MT, RM/MT and RM/LS (0.85-0.99) during side-lying forward flexion. Likewise, values <1 were found when MT (0.85) and LS (0.99) were involved with RM in the numerator during side-lying forward flexion. Ratios with Pm in the numerator showed values <1, apart from the ratios with UT and SA in the denominator. Conclusion: The study provides extended knowledge about the deeper-layer scapular muscle activity and related ratios during the 4 shoulder exercises mentioned here. Putting theory into practice, based on our results, we advise both side-lying exercises to be performed to strengthen LT and MT, even in case of hyperactivity of the Pm. However, the 4 exercises should be given carefully to patients with hyperactivity in the LS and/or RM. Clinical Relevance: The findings of this study may assist clinical decision making in exercise selection for restoring scapular function.

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.…”

“…It is widely recognized that scapular dyskinesis rehabilitation programs focused on decreasing UT activation and increasing SA and LT activation in early stages of the rehabilitation process contribute to restoring normal scapular position and movement ( Cools et al, 2007 ; Youdas et al, 2020b ; Berckmans et al, 2021 ). Several closed kinetic chain exercises have been reported as efficient to increase SA and LT myoelectrical activity, such as “push-up” ( Calatayud et al, 2014a ; Santos et al, 2018 ), “push-up plus” (scapular protraction posture in the end of the ascending phase of a push-up) ( Cools et al, 2014 ; Batbayar et al, 2015 ; Gioftsos et al, 2016 ; Hwang et al, 2017 ), “scapular protraction” (scapular protraction and retraction with elbows extended) ( Andersen et al, 2012 ; Lee, Lee & Park, 2013 ; De Mey et al, 2014 ), and “plank” (prone position, with the trunk and leg fully extended, the shoulders flexed at 90° and elbows in extension) ( Pontillo et al, 2007 ; Tucker et al, 2010 ; Ashnagar et al, 2016 ; Oliver et al, 2018 ).…”

Center of pressure (COP) measurement in patients with confirmed successful outcomes following shoulder surgery show significant sensorimotor deficits

“…Finally, a standardized method to assess the sensorimotor function of the shoulder is yet to be determined. Other commonly used methods are the joint position sense and kinesthesia examinations [26][27][28][29][30][31].…”

Analyzing Human Muscle State with Flexible Sensors

“…And EMG signals are measured to determine the electrical current generated by muscle contractions in neuromuscular activity [46]. Therefore, electromyography (EMG) is often used as a tool to determine muscle activity [47][48][49][50]. Bogey et al [44,51] recently developed a method to estimate force from EMG signals and based on normalization of activation during maximum voluntary contraction to record maximum muscle force.…”