Use of unstable exercises in periscapular muscle activity: A systematic review and meta-analysis of electromyographic studies.

BACKGROUND: The use of unstable surfaces has been proposed to increase the neuromuscular demand. This strategy has been adopted to generate an increase in the activity of periscapular muscles due to its role in the stabilization of the scapula. However, the influence of this instability on the EMG activity remains uncertain. The aim of this study was to analyze the effects of using unstable surfaces on the EMG activity of the periscapular muscles. METHODS: A comprehensive search in the PubMed, EMBASE, SCIELO, Web of Science, SCOPUS, Cochrane and LILACS databases was undertaken from their year of inception up to December 2019. Studies which directly investigated the EMG activity of periscapular muscles in healthy individuals while performing exercises for the upper limbs in stable and unstable conditions. RESULTS: A total of 33 studies which evaluated a total of 678 healthy individuals were found according to the eligibility criteria. A meta-analysis identified that the EMG activity of the upper trapezius showed a trivial increase with the insertion of the unstable surface (P = 0.04; SMD = 0.14 [95%CI 0.00, 0.27]). No significant effects were observed on the middle trapezius (P = 0.10) and lower trapezius (P = 0.25). A decrease of the anterior serratus EMG activity with a small effect size was observed by implementing an unstable surface (P = 0.01; SMD = -0.21 [95%CI -0.36, -0.05]). CONCLUSION: The use of unstable surfaces generated a trivial increase in the upper trapezius activity, and a slight decrease in the anterior serratus activity. No effect was observed on the middle and lower trapezius.

Electromyographic analysis of the serratus anterior and trapezius muscles during push-ups on stable and unstable bases in subjects with scapular dyskinesis.

The present study was performed to assess the electromyographic activity of the scapular muscles during push-ups on a stable and unstable surface, in subjects with scapular dyskinesis. Muscle activation (upper trapezius [UT]; lower trapezius [LT]; upper serratus anterior [SA_5th]; lower serratus anterior [SA_7th]) and ratios (UT/LT; UT/SA_5th; UT/ SA_7th) levels were determined by surface EMG in 30 asymptomatic men with scapular dyskinesis, during push-up performed on a stable and unstable surface. Multivariate analysis of variance with repeated measures was used for statistical analyses. The unstable surface caused a decrease in the EMG activity of the serratus anterior and an increase in EMG activity of the trapezius (p=0.001). UT/SA_5th and UT/ SA_7th ratios were higher during unstable push-ups (p=0.001). The results suggest that, in individuals with scapular dyskinesis, there is increased EMG activity of the trapezius and decreased EMG activity of the serratus anterior in response to an unstable surface. These results suggest that the performance of the push up exercise on an unstable surface may be more favorable to produce higher levels of trapezius activation and lower levels of serratus anterior activation. However, if the goal of the exercise program is the strengthening of the SA muscle, it is suggested to perform the push up on a stable surface.