The shoulder is the most flexible joint in the human body. It is also one of the most complex, with a greater range of motion than any other joint. It enables us to raise, bend, rotate and swing our arms. A properly functioning shoulder is not only critical to the golf game, but to many activities of daily living.
The shoulder is our most mobile, yet least stable joint. Its tremendous range of motion makes the shoulder less stable, and it is generally more prone to injury and dislocation than our other joints.
The shoulder is made up of three bones: the upper arm bone (humerus), the shoulder blade (scapula) and the collarbone (clavicle).
These bones are joined together by muscles, ligaments and tendons that support and stabilize the shoulder, allowing the arm to function.
The shoulder is composed of four joints:
- The glenohumeral joint is the main joint of the shoulder. It is where the rounded top part of the arm bone, the humeral head or "ball", meets the "socket" (glenoid) of the shoulder blade. This joint is referred to as a "ball and socket" joint in terms of its shape and function. The joint surfaces interact in a manner similar to a golf ball on a tee. The socket is very shallow and smaller than the ball, therefore the joint is inherently less stable than a true ball and deep socket, such as the hip joint.
- The sternoclavicular joint is the joint between the sternum (chest bone) and collar bones.
- The acromioclavicular joint, commonly called the AC joint, is where the collarbone meets the highest point of the shoulder blade (acromion).
- The scapulothoracic joint is between the rib cage and the shoulder blade
Shoulder Joint and Ligaments
Several important ligaments can be found in the shoulder joints. The primary function of the ligaments is to provide stability to the inherently unstable joint and to strengthen the capsule that surrounds the shoulder.
Many muscles are responsible for movement in the shoulder, but the primary muscle groups are the rotator cuff, the deltoid and the trapezius.
The rotator cuff is a group of muscles and their tendons that attach our upper arm to our shoulder blade. The most important job of the rotator cuff muscles is to provide stability for the ball (the end of the upper arm bone) in the socket and specifically center the ball within the socket during functional movements. The rotator cuff is also responsible for lifting the arm out to the side, as well as external and internal rotation of the shoulder.
The deltoid muscle group is responsible for shoulder flexion (raising our arm straight out in front), abduction (raising our arm directly out to the side), and extending our arm behind our back.
The trapezius is a large kite-shaped group of muscles extending from the low back to the neck. These muscles, known as "traps", are divided into an upper, middle and lower portion and work along with other muscles on the joints of the shoulder. The upper traps elevate the shoulder (shrug), the middle traps retract the shoulder (shoulder blade squeeze) and the lower traps depress the shoulder (shoulder blade pushed downward).
Normal Range of Motion
The normal range of motion of the shoulder can vary. A golfer who lacks normal range of motion may be at greater risk of shoulder injuries. The average golfer should have normal range of motion of the shoulder in three directions:
- Golfers should be able to comfortably raise their arms overhead
- They should be able to reach directly behind their back and touch the space between their shoulder blades with their thumbs
- They should be able to place their hands behind their head and open both elbows equally out to the side.