Biomechanics Blog 1: Reaching for Food

Each day, I reach into the refrigerator to grab food. I start with my arm in a relaxed position by the side of my body. This position is similar to anatomical position, but my hand faces towards my thigh instead of being in a supine position. In the final position, I flex my shoulder joint, extend my elbow and wrist joints, and flex my MTP, PIP, and DIP joints to grasp the item. These actions occur in the sagittal plane and about the coronal/frontal axis. The osteokinematic movement of the shoulder joint is flexion of an open kinetic chain from a relaxed, more extended position, and it comes from the concentric (isotonic) movement of the prime movers. These prime movers are the deltoid, coracobrachialis, and pectoralis major muscles. The arthrokinematics movement at the shoulder joint occurs between the glenoid fossa (concave) and the head of the humerus (convex). The head of the humerus rolls superiorly and glides inferiorly on the glenoid fossa.