Exploration of upper trapezius muscle activation during arm elevation with high-density electromyography

To explore muscle activation in different portions of UT during arm elevation using high-density EMG.To explore muscle activation in different portions of UT during arm elevation using high-density EMG.

Ten participants without shoulder and neck pain were recruited (6 males and 4 females, 1.69±0.08m, 62.4±8.47kg). Three measurements of scaption, shoulder abduction, and shoulder flexion were performed for the normalization process. The 32-channel (8 row*4 column) high-density surface EMG (TMSi, Enschede, The Netherlands) was used to collect UT muscle activation. The grid was applied on the right UT muscle, and the most proximal row was aligned with the margin of the UT. The root-mean-square values were analyzed for every 30-degree humeral-thoracic elevation from 30 to 120 degrees. Repeated measures of analysis of variances (ANOVAs) were used to assess the differences in muscle activation for different UT portions (rows) and elevation angles on muscle activation. The pairwise comparisons were conducted with Bonferroni corrections. The significance level was set at 0.05.

During shoulder abduction, significant row effects (F=8.175, p=0.005) were found, and the pairwise comparison indicated that the UT activation at the 8^th row was significantly higher than that of the 5^th row (p=0.034). During scaption and shoulder flexion, significant row effects (Scaption: F=4.650, p=0.033, Flexion: F=3.081, p=0.049) were also found; however, no significant pairwise comparison was identified. During arm elevation, there were no significant angle effects, indicating no significant difference in UT muscle activation for different arm elevation angle.

During arm elevation, different portions of the UT muscle seemed to have different activation levels. However, further research is needed to clarify the roles of different portions of the upper trapezius.

Different portions of the upper trapezius muscle might have different roles during arm elevation. Clinicians should take it into consideration when managing patients with upper trapezius dysfunction.