Natural Arm Movement

Hi all,

I'm wondering if there are any tricks that someone may have learned that can give a 2D cutout of a long sleeve shirt natural arm movement as you raise and bend the arm. I currently have a torso, an upper arm, an elbow (which is used as a patch when the upper and lower arm parts move), and a lower arm. I have set the pivot points at the joints for each part.

What I'm looking to do is make it look as natural as possible and not so stiff and mechanical. i.e., muscle movement, and cloth movement.

thanks,

Justin