Quick Hit Summary
A common source of shoulder pain is torn rotator cuff muscles or shoulder impingement. Shoulder impingement occurs when the deltoid muscles overpower the rotator cuff, resulting in the humeral head pinching the structures located under the acromion process. Thus, goal of rehabilitating this injury is maximizing the rotator cuff muscle activity while minimizing that of the deltoid. This is best accomplished through external rotation exercises. In contrast, commonly prescribed exercises such as full/empty can arm raises may flair up shoulder pain.
If I had to take a guess, I’d hypothesize that shoulder pain is one of the primary conditions treated by orthopedic doctors. I’m sure almost everyone has heard of individuals with rotator cuff problems. This is a common problem for many athletes, especially those whose sports requiring overhead throwing/hitting motions (volleyball, baseball pitchers). Shoulder problems also tend to pop up in individuals with muscle imbalances between the anterior and posterior sides of their upper body (Yes, I’m talking to all you out there who do nothing but bench press!!!!). These individuals will often appear to have rounded shoulders.
Shoulder pain can often be attributed to problems with the rotator cuff. To understand why this occurs, one must first understand the function of this muscle group. This muscle group is located on the posterior (back) side of the shoulder. It consists of the following 4 muscles:
- Teres Minor
Figure 1. This is a picture of the posterior side of the shoulder blade and upper arm bone. All the muscles of the rotator cuff except the subscapularis, which is located underneath the shoulder blade, can be seen. As one can tell by looking at the picture, these muscles are responsible for holding the “ball” of the upper arm into the shoulder socket.
Functions of the Rotator Cuff
The rotator cuff stabilizes the humeral head (ball part of upper arm bone) within the shoulder joint (See Figure 1). When this muscle group is weak it can cause excessive movement of the humeral head, especially with movements involving abduction (moving arm away from the side of your body). The rotator cuff is also extremely important during overhead throwing/hitting motions where it functions in decelerating the arm. Weakness in these muscles can cause a couple things to happen. First, one can tear there rotator cuff. This can happen over time or upon high impact situations. The second problem seen is a condition known as Shoulder Impingement Syndrome that results when the deltoid muscles overpower the rotator cuff, resulting in the humeral head pinching the structures located under the acromion process (bone at tip of top side of shoulder).
Recent Research on Rehabilitating the Rotator Cuff
In a recent study, Boettcher et al. noted that the most commonly injured of the rotator cuff muscles was the supraspinatus. During abduction of the arm, the supraspinatus prevents the deltoid muscles from pulling the humeral head up into the subacromial space (space just under the acromion process). Thus, the focus of Boettcher et al.’s study was to examine various exercises commonly recommended for shoulder rehab and to see which ones minimized deltoid activity while maximally working the supraspinatus. Using EMG readings (tool used to measure muscle activity during contractions), the group looked at 5 different exercises and muscle activity elicited during maximal voluntary isometric contractions. Description of the exercises and positions used for the isometric EMG testing are as follows:
1. Full Can: This exercise is completed while standing. Also one’s arms at their waist, thumbs up while holding a weight. The individual raises their arms up from there a 30º angle anterior to the frontal plane (the frontal plane can be thought of as an imaginary sheet of paper that separates the anterior side of your body from the posterior side of your body. Once the arms are at shoulder width height, the individual pauses and then lowers them back down to starting position.
: Shoulder abduction in the scapular plane (30º anterior to the frontal plane) with external rotation and resistance applied at the wrist.
2.Empty can: same exact movement as the “Full Can” except now the thumbs are pointed down, as if one was trying to empty a can of pop.
: Shoulder abduction in the scapular plane with internal rotation and resistance applied at the wrist.
3. Prone Elevation: This involves lying down on one’s stomach and raising their arm out in front of them (as if they were making a “Y” shape with their body). The arms are at ~100º angle with respect to the sides of the body.
: Shoulder elevation with the subject in prone, the shoulder abducted approximately 100º, the arm externally rotated, and resistance applied at the wrist.
4. Pendant External Rotation: This exercise is completed with a bungy/cable that is attached to a wall/exercise machine that is perpendicular to your body. While in the standing position, ones elbow is kept tight against his/her side (the arm being exercises is the one farthest from the wall). The individual then externally rotates (rotates arm outward) their lower arm while still keeping their elbow tight against their side.
: Shoulder external rotation in 0 º abduction with the elbow at the side and flexed 90 º – and resistance applied at the wrist.
5. Prone External Rotation. While lying on the stomach the upper arm is at a 90º with respect to the side of the body. The elbow is then flexed to a 90º angle. While maintaining these angles the hand (with or without weight) rotates towards the ground and then back up again.
: With the subject in prone, the shoulder abducted to 90º and the elbow flexed to 90º and resistance applied at the wrist to end range external rotation.
For all of these exercises, the shoulder blades should be held tight against the backside of the ribcage throughout the entire movement.
Results of the study showed that all exercises worked the supraspinatus muscle to the same degree. However, the prone elevation, empty can, and full can exercises significantly increased the activity of the deltoid muscles in comparison to the prone and pendent external rotation exercises. Thus Boettcher et al. conclude that their results.
“strongly indicate that exercises involving external rotation are preferable to empty can, full can, and prone elevation for specifically strengthening supraspinatus in subjects with normal dominant shoulder function.”
Study Limitations and Other Notes
There are a few limitations that should be mentioned regarding this study. First the measurements were obtained during isometric contractions (muscle contracting but no movement occurs). These exercises are commonly done in a dynamic fashion, thus muscle activity changes during the movement. Secondly, these results were completed in healthy individuals. For individuals that have already injured their shoulder, muscle activity may be slightly altered. However, based off these results, I’d still recommend the external rotation exercises for someone rehabbing their shoulder or trying to prevent shoulder injuries from happening in the first place (ie-prehab).
On a final note, I must emphasize the fact the rotator cuff/ shoulder pain can also result from weakness in other scapular muscles (middle trapezius, etc). Thus one should not focus solely on the muscles of the rotator cuff while trying to prevent/rehab shoulder problems.
Rotator Cuff Issues commonly pop up for most overhead sport athletes. When ones rotator cuff muscles are week, they can easily be torn under high velocity movements. Of the rotator cuff muscles, the supraspinatus is the one most commonly injured. In addition shoulder impingement can occur as the deltoid overpowers these muscles. Thus, if you’re having shoulder pain related to shoulder impingement you want to maximize activity of the supraspinatus while minimizing activity of the deltoid. This is best accomplished through external rotation exercises vs. the traditional empty/full can exercises.
Not to be forgotten, shoulder pain can also stem from weak scapular muscles such as the middle trapezius muscles, etc. Thus, if tolerable, include exercises targeting these muscles (ie- Scapular Wall Slides).
1 Boettcher CE, Ginn KA, Cathers I. Which is the Optimal Exercise to Strengthen Supraspinatus? Med. Sci. Sports Exerc., Vol. 41, No. 11, pp. 1979–1983, 2009.
2 Accessed June 16, 2010 from: commons.wikimedia.org/wiki/File:Shoulderjoint.PNG
3 Created by mcmorgan08. Accessed June 18, 2010 from: flickr.com/photos/mcmorgan/3113753707/