Characteristics of Scapular Muscles during a Side-lying-to-sitting Movement

Abstract

[Purpose] To clarify the characteristics of scapular muscles when sitting up from a side-lying position with the shoulder flexed at different angles. [Participants and Methods] Thirteen healthy adult males initially lay on the right side with the shoulder flexed at an angle of 0° (Condition 1) or 60° (2), and then moved to an on-elbow position (propping the upper body with one elbow to raise it). During this movement, muscle activity was measured with surface electromyography electrodes attached to 4 muscles: the posterior fibers of the deltoid, middle and inferior fibers of the trapezius, and external abdominal oblique. Comparing measurement values between the 2 conditions, the activity levels of the target muscles before/after peak contraction and after the end of the movement were calculated. [Results] The activity levels of the inferior fibers of the trapezius before/after peak contraction and those of all muscles after the end of the movement were higher under Condition 1 compared with 2. [Conclusion] The pattern of scapular muscle activity during a side-lying-to-sitting movement may vary according to the shoulder flexion angle in the initial position.