The next approach was based on a gravity effect: The muscle that was positioned against gravity worked the hardest ("muscle on top" approach). The limitations with this approach are similar to the observation of muscle development. More sophisticated approaches were based on the relationship of muscle length, type, position and mass. There was an assumption that if the muscle was positioned at its most biomechanically advantageous position, it would be the prime mover. This also turns out not to be true.
With the advance of electromyography (EMG), direct measures of activity could be used to determine how a muscle or muscles reacted to the demands of a given movement. Although there were numerous studies performed for shoulder exercises, the focus was on the use of small weights, body weight or isokinetic testing. Also, these studies often use one of two measures to determine the activity of a given muscle. Average amplitude is one measure used that has the disadvantages of averaging magnitude and duration and may not necessarily represent whether the muscle is active or not during a specific phase of movement.
A recent study1 has used elastic tubing to measure the activity of shoulder/scapular muscles. The investigators also took a novel approach to the display of EMG activity and combined both average amplitude and peak amplitude into the measurement. They followed these measures through the concentric and eccentric phase of the exercise. Additionally, they monitored the load being applied with each exercise. Some interesting results surfaced that may influence the type of exercises recommended, based not only on what muscles need rehabilitation but also at what phase of rehabilitation.
Seven core exercises were used in the study:
- Internal rotation -- The tubing is anchored at four feet. The subject stands with the arms held against the thorax, shoulders externally rotated 45 degrees, elbow flexed 90 degrees and arms stationary at the side.
- External rotation -- The tubing is anchored at four feet. The subject's arms are against the thorax, elbows flexed to 90 degrees and the forearms against the abdomen. The subject is instructed to externally rotate 90 degrees.
- Shoulder shrug -- The subject stands on the tubing, arms internally rotated, elbows extended and palms facing the body. The subject shrugs the shoulders, then retracts the shoulders, and then lowers the shoulders, keeping the arms in the same starting position.
- Forward punch -- The tubing is anchored at four feet. The subject stands with an initial position of the arms held against the thorax and elbows flexed 90 degrees. The subject punches forward to shoulder height with arms extended.
- Seated row (narrow grip) -- The tubing is anchored at one foot. Both handles of the tubing are grasped and then brought toward the chest.
- Seated row (medium grip) -- The tubing is anchored at one foot. Both handles of the tubing are grasped and then pulled to the width (outside) of chest.
- Seated row (wide grip) -- The tubing is secured at one foot. The tubing is grasped with palms down, elbows almost at shoulder height. The subject pulls toward the chest at shoulder height.
All exercises were performed slowly, with enough tension that the subject could perform 10 repetitions. Both the concentric and eccentric phases were performed.
The results of this study indicate that there may be some value in the use of elastic tubing for strengthening shoulder and scapular muscles. More specifically, certain exercises that have not been previously used as core exercises may have some advantages over other previously recommended exercises without putting the subject at risk if impingement syndrome or instability are present.
Here is a summary of some of the findings and recommendations. It is highly suggested to view the original article, which gives photo illustrations and graphs of activity that will assist in interpreting this summary.
- Shoulder shrug -- This was considered the most effective exercise with regards to how many muscles were active. High activity was noted for the subscapularis (especially during the retraction phase), trapezius and latissimus dorsi. Other muscles that were stimulated included the supraspinatus, infraspinatus and serratus anterior.
- Internal rotation -- This brings low levels of activity for a number of muscles including the subscapularis (which had higher activity with the shoulder shrug and narrow and middle-grip seated rows) and pectoralis major as the two main muscles, with lesser activity of the biceps, latissimus dorsi and serratus anterior.
- External rotation -- The infraspinatus was the primary muscle activated. There was moderate activity of the supraspinatus, subscapularis, pectoralis major and serratus anterior.
- Forward punch -- This was also considered a very effective exercise, with the greatest activity from the supraspinatus, serratus anterior and anterior deltoid; the pectoralis major and infraspinatus were also stimulated.
- Seated row (middle-grip) -- The main activity was in the supraspinatus and subscapularis.
- Seated row (wide-grip) -- This exercise brings the same activity as the middle-grip, with the addition of the trapezius and infraspinatus.
- Seated row (narrow-grip) -- This primarily activates the subscapularis.
The authors suggest that for the subscapularis, it might be appropriate to begin with internal rotation due to the low activity of the subscapularis. One would then progress to more demanding exercises such as the wide-grip seated row, then progress to the narrow and medium-grip seated row. In contrast, for all other muscles, the wide-grip seated row is considered a more advanced exercise.
The advantages of the exercises tested are that elastic tubing provides a constant resistance that allows both concentric and eccentric stimulation throughout the range-of-motion independent of position. The exercises presented were also performed at our below shoulder level, avoiding any aggravation of impingement. It is also important to note that biceps activity is relatively low throughout these exercises. (Personally, I find most patients over-contracting the biceps with shoulder exercise programs leading to aggravation or new injury.)
- Hintermeister RA, Lange GW, Schultheis JM, Bey MJ, Hawkins RJ. Electromyographic activity and applied load during shoulder rehabilitation exercises using elastic resistance. Am J Sports Med 1998;26(2):210-220.
Thomas Souza, DC, DACBSP
San Jose, California