That's great you're noting the strain it would cause, but I still don't see how the limb could move at all. It'd be like having the top and bottom of a conveyor belt move parallel to each other, if you get my drift. Poor simile aside, I'm pretty sure you wouldn't be able to move the limb. At all.
Like when you flex your arm. The bicep contracts so you can pull up your forearm, while the lower muscle relaxes. Extending the arm works vice versa. Doing both at the same time wouldn't really do much of anything, besides put stress on the bone and move nothing I'm pretty sure. You could probably build up more force by swinging your arm and using momentum than just... not moving at all.