Biomechanics of Sipping Coffee

An action that I do everyday, several times a day is taking a sip from my cup of coffee. As I hold my coffee mug and pull it toward my mouth, my shoulder flexes, elbow flexes, and fingers flex. The motions of flexing my shoulder, elbow, and fingers occur in the sagittal plane about the frontal axis. The osteokinematics of all of of these motions are open chain kinematics because the distal segments are moving. Regarding arthrokinematics as you flex the shoulder to take a sip, the convex humeral head rolls superiorly and glides inferiorly in the concave glenohumeral fossa of the scapula. At the elbow, the concave head of the ulna rolls and slides along the convex trochlea of the humerus. In flexion, the concave ulna rolls superiorly and glides superiorly along the convex humerus. The primary mover of shoulder flexion is the anterior fibers of deltoid that works concentrically to flex the shoulder.  The primary mover in elbow flexion is the biceps working concentrically to move the forearm. The primary mover in finger flexion is the flexor digitorum profundus which is performing a concentric action to keep the fingers flexed around the mug.