Activity Analysis- Eating a Meal

One movement that is part of my routine is eating a meal. This starts with me in a seated position with my arms at my side. The first movement done is reaching forward to pick up a fork which creates flexion at the shoulder and extension at the elbow. Flexion and extension both take place in the sagittal plane around the frontal axis.  The flexion at the shoulder has the glenoid fossa of the scapula (concave) stationary while the humerus (convex) rotates on it. The head of the humerus rolls back and slides down to achieve this movement. The prime mover of this action at the shoulder is the anterior deltoid completing a concentric contraction. For extension at the elbow, the distal end of the humerus (convex) remains stationary while the proximal end of the ulna (concave- trochlear notch) glides back. The prime mover of this movement due to gravity is the biceps brachii contracting eccentrically in order to control the movement. When the effects of gravity are not present, the triceps brachii act as a prime mover in elbow extension.

Once my arm is extended, I have to grab my utensil. To complete this movement, I have to flex my MCP, PIP, and DIP joints. For each of these joints, there is a concave proximal end that glides on the distal convex end of the previous bone. The prime movers in the flexion of these joints are the flexor digitorum profundus and superficialis and the flexor digiti minimi through concentric contractions. The thumb also flexes at the IP joint through the concentric contraction of the flexor pollicis longus. The flexion of the thumb takes place in the frontal plane and around a sagittal axis whereas flexion in the fingers takes place in the sagittal plane around a frontal axis. 

The last major movement is to bring the fork to my mouth.  This movement requires the flexion of my elbow and extension of my shoulder, so the plane of motion and axis of rotation are the same as reaching for a fork. In shoulder extension, there is the same articulation between the scapula and the humerus, but it rotates and slides in the opposite directions (rolls forward and slides up). Some prime movers of this movement are the posterior deltoid and the latissimus dorsi muscles when gravity is not a factor. Since gravity is applied in this situation, the anterior deltoid is contracting eccentrically to control the movement back down. In elbow flexion, the articulation is also the same between the ulna and the humerus, but the ulna glides forward on the humerus instead of back. The prime mover in elbow flexion is the biceps brachii contracting concentrically. Throughout this step, the phalanges stay in flexion holding onto my utensil.

Breaking down the steps and all the moving parts in an activity really leave me marveling at how complex and intricate seemingly basic activities can really be.