OT430 Blog 1: Activity Analysis

Every day I grab a coffee mug out of my kitchen cabinet. When I arrive at the cabinet and face it, my arm is in full adduction by my side. My forearm is in a neutral position and in full extension at the elbow joint, and palms facing in toward my body. In order to reach for my mug my shoulder must first go into concentric flexion to the height of the mug inside the cabinet. All of my DIP, PIP, and MIP joints go into concentric flexion as well as my thumb going into opposition in order to grasp and hold the mug. After I have grasped the mug, my elbow goes into concentric flexion in order to bring the mug in closer to my body meanwhile my shoulder is performing extension by eccentric muscle contraction to bring my arm back beside my body lowering the mug. The action of flexion and extension in the shoulder joint, elbow joint, as well as the DIP, PIP, and MIP joints takes place in the sagittal plane around a frontal axis. The osteokinematics of the shoulder is flexion to extension in an open kinematic chain. The arthrokinematics of the shoulder in flexion is the convex segment of the humerus spins and rolls inferiorly with a slight anterior glide within the stable  concave segment of the glenoid fossa on the scapula. The prime movers for the shoulder flexion is the anterior deltoid and coracobrachialis which perform a concentric contraction. The same muscles act in an eccentric manner to allow shoulder extension.