Scapulothoracic muscle activity and recruitment timing
Correct functioning of the scapulothoracic joint is essential for load transfer between the trunk and the upper extremity. This largely depends on sufficient activity levels and adequate recruitment timing in the periscapular musles: among others the upper, middle and lower trapezius (UT, MT and LT, respectively) and the serratus anterior (SA). Dysfunction in the scapulothoracic joint have been linked to the development of a number of shoulder disorders.
A systematic review of the literature regarding scapulothoracic muscle activity and recruitment timing (measured by EMG) in patients with and subjects without SIS and glenohumeral instability was conducted. 191 relevant articles were obtained, of which 12 were included for analysis in this review after screening and exclusion procedures.
It was found that generally, in patients with subacromial impingement syndrome, the UT showed increased activity whereas the LT and SA demonstrated a decrease in activity levels compared to asymptomatic controls. The relationship between instability in the glenohumeral joint and activity levels and recruitment timing remains unclear. Furthermore, no conclusive evidence was present on patterns in timing of muscle recruitment.
> From: Struyf et al., J Electromyogr Kinesiol 24 (2014) 277-284. All rights reserved to Elsevier Ltd. Click here for the Pubmed