As the upper extremity progresses to higher levels of elevation, the moment arm for the lower trapezius to upwardly rotate the scapula becomes larger.

Question

Quizplus · Accepted Answer

The moment arm is the distance between the point of force application and the axis of rotation. As the upper extremity elevates, the line of pull of the lower trapezius on the scapula becomes more perpendicular to the spine, increasing the moment arm and therefore its ability to upwardly rotate the scapula.

As the Upper Extremity Progresses to Higher Levels of Elevation