Human Body Biomechanics for Beginners: Part II: Shoulder Joint

Your upper arm bone (humerus) moves in the shoulder (glenohumeral) joint. This joint is the most mobile joint in the human body. 

This column will give you a basic introduction to your humerus, commonly known as your arm bone, and your glenohumeral joint, commonly known as your shoulder joint. It is designed to help you become more aware of your movements at this joint.  

Your humerus is a long bone and the only bone in your upper arm. It is located between your shoulder and your elbow. The plural of humerus is humeri. 

The head of the humerus is shaped like a ball. It sits in a shallow socket on the upper outside of the scapula. This ball and socket create the glenohumeral joint, or the shoulder joint. 

Your shoulder joint is the most mobile joint in your body. The head of the humerus fits very loosely in the socket, similar to the way that a golf ball fits on a tee. Ligaments, tendons, and muscles help keep the humerus centered in the socket. Thank goodness! 

High mobility in your shoulder joint creates a very vulnerable environment that puts your shoulder joint at risk for injury. Especially as you, and everyone of us, continue, over the years, to overuse, underuse, and abuse with repetitive, compensatory movement at this joint.  

The head of the arm bone moves in the shoulder joint in 8 directions in 4 pairs. 

The head of your arm bone moves in your shoulder joint in 8 directions, in 4 pairs. You can try these pairs of movements for yourself.  

Note: Don’t confuse “shoulder joint” movement and “shoulder blade” movement. When someone says “my shoulder hurts”, they may be referring to pain in the shoulder joint. But they may also be referring to pain in the shoulder blades, which rest on the upper back. Check out last week’s column for a discussion of the shoulder blades. 

Start standing with your arms at your side body. This is called the “anatomical position”. All of the instructions below assume that you are starting from the “anatomical position.”  

1. abduction – adduction 

a.  Lift your arms up and out to the side. 

b.  Lower your arms back to your side. 

2. flexion – extension 

a.  Lift your arms up in front of you. 

b. Lower your arms back to your side and bring them behind you. 

3. internal shoulder rotation – external shoulder rotation 

a. Rotate the head of your arm bone so that your elbow faces forward. Be sure to initiate this movement at  the head of your arm bone, not at your elbow or wrist. 

b. Rotate the head of your arm so that your elbow moves behind you. Be sure to initiate this movement at the head of your arm bone, not at your elbow or wrist.  

Note: You can rotate your shoulders internally or externally while you are moving in the other directions described here. E.g., in flexion, extension, abduction, adduction, horizontal abduction, and horizontal adduction.  

4. Horizontal abduction – horizontal adduction 

a. From the anatomical position, lift your arms forward in front of you. Then move your arms out to the side (horizontal abduction). 

b. From the anatomical position, lift your arms out to the side. Then move your arms forward in front of you (horizontal adduction).  

Move your arm bones the way they are designed to move. Notice what is working and what is not. 

Are you experiencing pain, tightness, or tension in your shoulders or your upper arms? When your upper arm bone is not moving well, your arms will not move freely. Your movement will be limited. You may experience a great deal of pain and discomfort. 

Practice the movements listed above. The more often, the better. Move slowly, paying attention to your movement and your breath. Arm yourself with the knowledge of how your upper arm bones move (pun intended). Notice what is working when you move and what is not working. With that awareness, you will be able to create healthier movement patterns. 

Remember to keep your movements pain-free. If you meet tension, tightness, or pain in your movement, make it slower, smaller, or stop altogether. 

Healthy movement patterns at your shoulder joint will support your everyday movements. And improve your athletic endeavors. You will be able to reach a high cupboard, lift your grandchildren, and play better tennis and golf, and more! 

Medical Disclaimer: This article contains information intended to assist you in improving your health and well-being. However, the information presented is offered only as-is for informational and educational purposes. It is not a substitute for the professional judgment of a medical professional.

Via Anderson, E-RYT, is a Yoga and movement coach and teaches the Intelligent Movement Forever system of healthy movement in a weekly online class, in private sessions, and at Yoga Vallarta during the high season. This 77-year-old grandmother practices what she preaches and teaches. She is the author of “How to Move Without Pain: A Compendium of Intelligent Movement”, to be released in 2019. www.intelligentmovementforever.com