Shoulder pain is a common complaint, especially for those of us whose leisure and occupation require repetitive overhead motion. Whether it’s landscaping, painting, exercise, or throwing, overhead use of your arm can result in injury. The structure of the shoulder joint is similar to that of a ball and socket, allowing for a wide range of motion, making it the most mobile joint in the body.(1) This wide range of motion; however, comes with a price. Overhead activity requires an adequate balance of shoulder mobility with dynamic stability to prevent injury.
Anatomy
The shoulder joint is complex; it requires synchronous movement from your humerus (upper arm bone), scapula (shoulder blade) and clavicle (collar bone). The head of the humerus fits into a rounded socket on your scapula called the glenoid fossa (you can think of this as a golf ball on a tee), while the clavicle forms a joint with the scapula to allow for additional flexibility. The rotator cuff is the dynamic stabilizer of the shoulder; it is made of up four muscles and is responsible for providing stability of the shoulder joint.(3) The bursa lies between the rotator cuff and the acromion (top of the scapula) to allow for smooth motion.
Injury Resulting from Overhead Activity
You may have heard of impingement syndrome. Impingement occurs when subacromial space narrows and compression of the tendon and bursa results. Consistent impingement often results in inflammation and pain. Impingement of the shoulder is common, accounting for 44-65% of all shoulder complaints in primary health care.(2) As you raise your arm, the subacromial space naturally narrows; this is especially true at 90 degrees abduction, or when your arm is at shoulder height and out to the side. The space narrows more when 45 degrees internal rotation is added, placing the greatest injury risk to the supraspinatus muscle. (4) When our daily activites consist of repetitive overhead activity, this can turn into a vicious cycle of pain and inflammation.
Impingement can be caused by several factors both structural (such as a bone spur) and functional (such as muscular weakness/imbalance).(5) It is also important to consider our posture, as the position of our thoracic spine affects how the shoulder blade moves.(6) Research suggests that when we “slouch”, it results in decreased muscle force and range of motion when lifting our arm out to the side.(6) It should come as no surprise that having a slouched posture and working overhead can be a risk factor for impingement syndrome. Much research has been conducted on overhead athletes with shoulder impingement, suggesting muscle imbalance, primarily increased upper trapezius activation(7) and decreased serratus anterior/lower trapezius activation(8) can result in abnormal positioning of the shoulder blade and instability. To further contribute, stiffness through the mid back (thoracic spine) can block normal motion and tilting of the shoulder blade, further narrowing the subacromial space and causing impingement syndrome.
In most cases of shoulder impingement, you’ll need to address the cause of injury by restoring muscle balance in terms of flexibility and strength. A focus on spine mobility is important, too. For those who are painful modifying your activity to limit repetitive, overhead motion along with a focus on posture is a good place to start. At the gym, you’ll want to refrain from military press or front and lateral raises. In addition to traditional rotator cuff strengthening, a focus on scapulothoracic muscle strengthening (especially the serratus anterior and lower trapezius) should be incorporated into your exercise program.
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References:
1. Quillen DM, Wuchner M, Hatch RL. Acute shoulder injuries. Am Fam Physician. Nov 15 2004;70(10):1947-54.
2. Van der Windt D.A., et al. Shoulder disorders in general practice: prognostic indicators of outcome. Br J Gen Pract. 1996; 46:519-523.
3. Escamilla RF, Hooks TR, Wilk KE. Optimal management of shoulder impingement syndrome. Open Access Journal of Sports Medicine. 2014;5:13-24.
4. Graichen H., et al. Subacromial space width changes during abduction and rotation- a 3/D MR imaging study. Surg Radiol Anat. 1992:21(1):59-64.
5. Page P. Shoulder muscle imbalance and subacromial impingement syndrome in overhead athletes. Int J Sports Phys Ther. Mar 2011; 6(1):51-58.
6. Kebaetse M, McClure P, Pratt NA. Thoracic position effect on shoulder range of motion, strength, and three-dimensional scapular kinematics. Arch Phys Med Rehabil. 1999 Aug;80(8):945-50.
7. Cools A.M., et al. , Trapezius activity and intramuscular balance during isokinetic exercise in overhead athletes with impingement symptoms. Scand J Med Sci Sports. 2007;17(1):25–33
8. Cools A.M., et al. , Evaluation of isokinetic force production and associated muscle activity in the scapular rotators during a protraction-retraction movement in overhead athletes with impingement symptoms. Br J Sports Med. 2004;38(1):64–68.
