Differential activation of scapular muscles, during arm elevation, with and without trigger points

Background: Latent Myofascial Trigger Points (LMTrPs) are defined as certain pain-free hyperirritable spots in a muscle taut band which lead to muscle activation pattern alternation in both loaded and unloaded conditions during scaption. The current study aimed to investigate the onset of upward scapular rotator muscle activations during rapid arm elevation in three planes of movement in patients with upper trapezius LMTrPs compared to healthy control participants. Method: Three planes of scapular movement were evaluated. The onset of Deltoid (DEL) was considered as the starting point in marking the onset of Upper Trapezius (UT) and Serratus Anterior (SA) muscle activations. Results: There were significant differences in the relative muscle latencies between the LMTrPs and the control group. Those with LMTrPs showed a delayed and inconsistent activity of UT during all three planes of elevation (< 0.05) and the same pattern happened for SA during flexion (< 0.05). Conclusions: Both hosted and synergistic muscles experience delay in muscle activation and alterations in their recruitment pattern during rapid arm elevation in all planes of movement. These changes may serve as adaptive motor control strategies due to the presence of LMTrPs in UT muscles. © 2015 Elsevier Ltd