Everyday Action

Every morning when I leave for school, I have to open the door to my apartment. When I reach out to twist the door knob to open the door, my elbow extends, my shoulder flexes just a little, and there is slight supination of the forearm. As I open the door my elbow flexes, shoulder goes back in a neutral position (0°) and my forearm stays supinated. Flexion and extension of the elbow and flexion of the shoulder are in the sagittal plane about a frontal axis. Supination of the forearm is moving within the transverse plane about a vertical axis. The osteokinematics of the elbow are extension to flexion in a closed kinematic chain. As for arthrokinematics, the moving ulna is the concave part which glides in the same direction on the stable convex part of the humerus. The prime movers for elbow flexion are the biceps brachii, brachioradialis, and brachialis, which results in a concentric contraction.