Every morning I retrieve and drink orange juice from my refrigerator.
The starting position of my right arm is elbow extension by my side and it is functioning in a sagittal plane about a frontal axis. Next, I reach forward to open the refrigerator door. My right hand grips the refrigerator door and pulls back. Here, my elbow is moving into flexion as it pulls the refrigerator door back. During this movement, my right shoulder experiences slight shoulder extension, and the end position of my right arm is elbow flexion.
Next, I reach forward with my left arm towards the orange juice. The starting position of my left arm is elbow extension by my side, and my left shoulder is flexed, which are both functioning in a sagittal plane about a frontal axis. After I have grasped the orange juice with my left hand, I pull the orange juice towards my mouth. The end position of my left arm is flexion at the elbow, which occurs in the sagittal plane about a frontal axis.
The osteokinematics of the left elbow is extension to flexion in an open kinematic chain.
In terms of arthrokinematics, elbow flexion occurs at the humeroulnar and humeroradial joints. For the humeroulnar joint, the concave ulnar segment rolls and glides anteriorly on the stable, convex humerous. For the humeroradial joint, the concave radial head rolls and glides anteriorly on the stable, convex humerous.
The prime movers for elbow flexion are the biceps brachii, brachialis, and brachioradialis muscles, which perform a concentric contraction.
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