New research is showing that muscle is not what we think it is.
http://www.anatomytrains.com/ligaments
“This means that the ligaments, far from being active only at the moment of the greatest elbow extension in your preacher curl, are dynamically active in stabilizing the joint all through the movement, during both concentric and eccentric contraction. This muscle-ligament combination Jaap termed a ‘dynament’ (by a contraction of ‘dynamic ligament’) and the implications of his findings are profound.”