Shoulder muscle activation in closed kinetic chain exercises
Exercises targeting the middle (MT) and lower trapezius (LT) and serratus anterior (SA) with low activation levels of the upper trapezius (UT) and other major muscle groups are often advocated in the rehabilitation of shoulder pathologies. On top of that, closed kinetic chain exercises trigger mechanoreceptors and elicit activity in the stabilizing muscles around the shoulder complex.
In this study, 47 healthy subjects performed four different exercises aimed at training the MT, LT and SA, each exercise both on a stable and an unstable surface. Muscle activation levels were recorded using surface EMG, EMG activation levels were normalized and scapular muscle ratios (i.e. UT/MT, UT/LT and UT/SA) were calculated. The exercises included half push up, knee push up, knee prone bridging plus and pull up.
Generally, the scapular muscles showed lower activation levels and the glenohumeral muscle showed higher activation levels when the surface was unstable; especially the amplitude of SA activation and of pectoralis major activation showed a distinct decrease and increase, respectively. Concerning scapular muscle activation ratios, for all exercises included, unstable surface was not significantly better than a stable surface.
> From: De Mey et al., J Strength Cond Res 28 (2014) 1626-1635. All rights reserved to National Strength and Conditioning Association. Click here for the Pubmed summary.