Influence of muscle stiffness on scapular movement during arm elevation in elderly people

This study examined the influence of trapezius muscle stiffness on scapular movements, involving 24 elderly females without shoulder disorders. The degree of stiffness was measured at 3 points: the upper, middle, and lower parts of the trapezius. The females performed scapular elevation within the arm elevation range between 30 and 120° as a motor task to calculate the scapular upward rotation, posterior tilt, and external rotation angles. Each muscle stiffness (mean ± SD) were as follows: upper: 1.0±0.2 N; middle: 1.2±0.2 N; and lower: 1.5±0.1 N. The muscle stiffness of the lower trapezius showed a significant negative correlation with the scapular posterior tilt angle when elevating the arm at 90°(rs=-0.41 p<0.05) and 120°(rs=-0.43 p<0.05). Trapezius muscle stiffness was not significantly correlated with any other scapular movement. Based on the results, the scapular posterior tilt angle after the middle phase of arm elevation may decrease with an increase in the stiffness of the lower trapezius muscle.