Abstract
The intended scapular motion is a strategy to strengthen the lower trapezius (LT). However, few studies have explored the effects of the intended scapular posterior tilt motion on selective LT activation. Thus, the present study investigated the effect of the intended scapular posterior tilt on the electromyography (EMG) activity of trapezius muscles during prone shoulder horizontal abduction (PSHA). Eighteen asymptomatic men performed three types of PSHA: (1) preferred PSHA, (2) PSHA with the intended scapular posterior tilt, and (3) PSHA with the intended scapular posterior tilt and trunk extension. EMG activity of the upper trapezius (UT), middle trapezius (MT), and LT were measured during PSHAs. Scapular posterior tilt angle, with and without the intended scapular posterior tilt, were measured using inclinometer. The results indicated that LT muscle activity increased when scapular posterior tilt was applied with and without trunk extension (14–16%), compared to the preferred condition, during PSHA (p < 0.05). However, the addition of trunk extension to PSHA with the intended scapular posterior tilt increased the UT muscle activity (28%) and the UT/LT (29%) and UT/MT (31%) ratios (p < 0.05). The scapular posterior tilt angle was higher (15%) when applying the intended scapular posterior tilt (p = 0.020). These findings suggest that the intended scapular posterior tilt may be a useful strategy for selective LT muscle activation.
Highlights
Altered scapular movement or position can lead to various shoulder injuries, including subacromial impingement, rotator cuff disease, and superior labral injury [1,2,3,4]
The trapezius muscle EMG data obtained for all prone shoulder horizontal abduction (PSHA) conditions are shown in posterior tilt with and without the intended scapular posterior tilt were an
No significant change in upper trapezius (UT) muscle activity was detected between the preferred PSHA and PSHA with the intended scapular posterior tilt (p = 1.000)
Summary
Altered scapular movement or position (i.e., scapular dyskinesia) can lead to various shoulder injuries, including subacromial impingement, rotator cuff disease, and superior labral injury [1,2,3,4]. A crucial factor for altered scapular movement and/or shoulder injury is imbalanced scapular muscle activation [3,4,5,6], which includes reduced activity of the lower trapezius (LT) or middle trapezius (MT) muscle and enhanced activity of the upper trapezius (UT) [6,7,8]. Previous studies have shown elevated UT/LT activity ratios during arm elevation [8] and enhanced UT muscle activity, together with reduced MT and LT muscle activities, during shoulder abduction and external rotation [7] in individuals with subacromial impingement, compared with healthy individuals. The LT contributes to scapular upward rotation and posterior tilt, increasing the space in the subacromial region; this allows efficient glenohumeral joint movement [5,10,11]
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