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

Abstract

Background Multiple investigations have compared the electromyographic (EMG) activity of the scapular muscles between stable and unstable support surfaces during the execution of closed kinetic chain exercises. However, these comparative analyses have grouped different unstable surfaces (wobble board, BOSU, therapeutic ball, and suspension equipment) into a single data pool, without considering the possible differences in neuromuscular demand induced by each unstable support surface. This study aimed to analyze the individual effect of different unstable support surfaces compared to a stable support surface on scapular muscles EMG activity during the execution of closed kinetic chain exercises. Methodology A literature search was conducted of the Pubmed Central, ScienceDirect and SPORTDiscus databases. Studies which investigated scapular muscles EMG during push-ups and compared at least two support surfaces were included. The risk of bias of included articles was assessed using a standardized quality assessment form for descriptive, observational and EMG studies, and the certainty of the evidence was measured with the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. A random-effects model was used to calculate effect sizes (ES, Hedge’s g). Results Thirty studies were selected in the systematic review. Of these, twenty-three low-to-high quality studies (498 participants) were included in the meta-analysis. The main analyzes revealed, in decreasing order, greater UT EMG activity during push-ups performed on suspension equipment (ES = 2.92; p = 0.004), therapeutic ball (ES = 1.03; p < 0.001) and wobble board (ES = 0.33; p = 0.003); without effect on the BOSU ball. In addition, no effect was observed for SA on any unstable device. The certainty of the evidence ranged from low to very low due to the inclusion of descriptive studies, as well as high imprecision, inconsistency, and risk of publication bias. Conclusion These findings could be applied in scapular muscles strengthening in healthy individuals. The use of suspension equipment achieves higher UT activation levels. Conversely, the use of any type of unstable devices to increase the activation levels of the SA in shoulder musculoskeletal dysfunctions is not recommended. These conclusions should be interpreted with caution as the available evidence showed a low to very low certainty of evidence, downgraded mostly by inconsistency and imprecision.

Comparison of the Electromyography Activity during Exercises with Stable and Unstable Surfaces: A Systematic Review and Meta-Analysis

“…It is difficult to discuss the findings for the other muscles evaluated, since there are few studies, and none of them had quantitative data. The results of the present study contribute to understanding the effect of adding unstable surfaces on the agonist muscles since systematic reviews have focused on the role of the stabilizer muscles [ 21 , 22 ].…”

“…Only two systematic reviews have compared the effects of using unstable surfaces on electromyographic activity, and both only evaluated periscapular muscles [ 21 , 22 ]. The first study included 33 studies that evaluated 678 subjects and showed that using unstable surfaces generated a slight increase in upper trapezius activity and a slight decrease in serratus anterior activity.…”

“…The second study evaluated whether different types of instability devices provide different EMG responses in the serratus anterior and upper trapezius muscles. The authors verified that only the suspension straps increase the upper trapezius activity and that any instability device decreases the serratus anterior activity [ 22 ].…”

A comparative electromyographic study of scapular stabilizing muscles during five main rehabilitation exercises

“…5,[9][10][11] This impairment of neuromuscular control has been widely detected by surface electromyographic (sEMG) amplitude of the scapular stabilizing muscle (serratus anterior [SA], middle trapezius [MT], lower trapezius [LT], and upper trapezius [UT]), through certain criteria such as low activation amplitude, muscle imbalance (i.e., altered activation ratio), and delayed onset latency. 1,4,9,12 Thus, sEMG amplitude values ≥50% maximum voluntary isometric contraction (MVIC) are categorized as optimal for activation of the scapular stabilizing muscle, facilitating the interpretation of sEMG amplitude in research and clinical practice. 8 Furthermore, optimal muscle balance has been investigated using the activation ratio, that is, the relative activity of one muscle versus another rather than the absolute value of sEMG amplitude.…”

“…Altered scapular position and movement is often caused by an imbalance of agonist and antagonist muscles, either by inhibition or overactivity of the scapular muscles 5,9–11 . This impairment of neuromuscular control has been widely detected by surface electromyographic (sEMG) amplitude of the scapular stabilizing muscle (serratus anterior [SA], middle trapezius [MT], lower trapezius [LT], and upper trapezius [UT]), through certain criteria such as low activation amplitude, muscle imbalance (i.e., altered activation ratio), and delayed onset latency 1,4,9,12 . Thus, sEMG amplitude values ≥50% maximum voluntary isometric contraction (MVIC) are categorized as optimal for activation of the scapular stabilizing muscle, facilitating the interpretation of sEMG amplitude in research and clinical practice 8 .…”