Scapular muscle-activation ratios during shoulder exercises
While the theoretical concept of altered scapular muscle balance in patients with shoulder injuries is generally accepted, and exercises are widely prescribed to improve scapular muscle strength and coordination, evidence on activation of the upper, middle and lower trapezius (UT, MT and LT, respectively) and serratus anterior (SA) remains inconclusive.
In this study, 39 subjects (20 patients with shoulder injuries and 19 asymptomatic controls) performed four functional shoulder exercises: the bow and arrow (BA), external rotation with scapular squeeze (ERSS), lawnmower and robbery exercise. Surface electromyography was used to record activation of the UT, MT, LT and SA – all values were normalized and muscle-activation ratios were calculated.
For none of the activation ratios (UT:MT, UT:LT and UT:SA), significant differences were found between groups, although trends towards group differences were present, indicating more UT activation in the injury group. Significant differences in activation ratios and individual muscle activation were present between exercises: the BA exercise elicited the highest activation ratios (i.e. relatively high UT activation) while the lowest UT activation was present in the ERSS exercise.
> From: Moeller et al., J Athl Train 49 (2015) 345-355. All rights reserved to the National Athletic Trainers’ Association, Inc. Click here for the Pubmed summary.