Activation of the trapezius muscle during varied forms of Kendall exercises

The trapezius muscle plays a crucial role in maintaining proper shoulder mechanics and is often considered a source of weakness and dysfunction in patients.

The purpose of this study was to investigate the activation patterns of the middle and lower trapezius during four prone horizontal abduction exercises of the glenohumeral joint (GHJ).

The muscle activation patterns of 19 female and 13 male volunteers were measured using surface EMG during horizontal arm abduction exercises commonly used in rehabilitative settings. Each subject performed 10 repetitions of horizontal abduction (ABD) at each position using only the weight of the arm. Function was assessed during shoulder horizontal abduction while positioned at: 75 degrees , 90 degrees , 125 degrees and 160 degrees of GHJ ABD. Electromyographic activity was collected during the concentric phase during each test repetition in the lower (LTRAP) and middle trapezius (MTRAP). A repeated measure ANOVA was performed followed by Bonferroni's post hoc test.

The MTRAP had significantly greater recruitment at 90 degrees and 125 degrees , compared to 160 degrees . Similarly, results for the lower trapezius indicated that recruitment at 90 degrees and 125 degrees was significantly greater than 160 degrees .

Most significant muscle activation for the middle and lower trapezius occurred at 90 degrees and 125 degrees of GHJ ABD. For the clinician, training at 90 degrees is easy to identify, and provides maximal activation, negating the need for multiple training angles.