The brachialis muscle has attachments to the anterior portio…

The brachialis muscle has attachments to the anterior portion of the distal half of the humerus and the anterior portion of the proximal ulna.  The main action of the brachialis muscle is forearm or elbow flexion.  Knowing this you can deduce that the ______________ occurs at the more stable, humerus part with the ____________ being at the more mobile ulnar attachment.