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 series is designed to give you a basic introduction to how various parts of your body move. Knowing these basics will help you become aware of your movements and move better.
Part II of this series will introduce you to the movements of your upper arm bone, commonly known as the humerus.
Your humerus is a long bone and the only bone in the upper arm. It is located between the shoulder and the 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, commonly called the shoulder joint.
The shoulder joint is the most mobile joint in the human 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!
The head of the arm bone moves in the shoulder joint in 8 directions in 4 pairs.
The head of the arm bone moves in the shoulder joint in 8 directions in 4 pairs. You can try these pairs of movements for yourself. Start standing with your arms at your side body. This is 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 the arm bone so that the elbow faces forward. Initiate this move at the head of the arm bone, not the elbow.
b. Rotate the head of the arm so that elbow moves behind you. Initiate this move at the head of the arm bone, not the elbow.
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).
When you move your arms in a big circle at the shoulder, involving all 8 directions of movement, it is called circumduction.
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. Part I of this series addressed human body biomechanics at the shoulder blade.
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. You may experience a great deal of pain and discomfort.
Practice the movements listed above. Arm yourself with the knowledge of how your upper arm bones move. 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 the shoulder joint support your everyday movements. And improve your athletic endeavors.
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.