Abstract
Shoulder horizontal abduction exercise in the prone position is effective for
strengthening the lower trapezius muscle. However, this exercise is difficult
for patients with acute pain or those undergoing initial rehabilitation because
of the postural characteristics of the exercise. This study aimed to (1)
investigate the effect of a shoulder horizontal abduction exercise when
performed with a different amount of shoulder rotation on the trapezius muscle
activation and scapular anterior/posterior tilt angle and (2) evaluate the
effect of shoulder rotation on the acromiohumeral distance while sitting.
Fifteen healthy men performed shoulder horizontal abduction exercise in three
shoulder positions (internal rotation, neutral rotation, and external rotation).
During exercises, we measured trapezius muscle activity using an
electromyography system and scapular anterior/posterior tilt angle using an
inclinometer application. We also measured the acromiohumeral distance using
real-time ultrasonography before the exercises. Increases in lower trapezius and
middle trapezius muscle activities and a decrease in scapular anterior tilt
occurred in shoulder external rotation compared with other positions
(p<0.001). Shoulder external rotation also significantly increased
acromiohumeral distance in the sitting position (p<0.05). We propose that
shoulder external rotation effectively and safely increases middle and lower
trapezius muscle activities during the sitting shoulder horizontal abduction
exercise.
Keywords
acromiohumeral distance - electromyography - lower trapezius
