Shoulder muscle activation levels during range of motion exercises
May 17, 2012
Shoulder rehabilitation patients often perform range of motion exercises using shoulder pulleys and bars. These “active-assisted” exercises are often used as the next-step in shoulder rehabilitation after passive range of motion (ROM) exercises. Active-assisted range of motion (AAROM) exercises are usually performed to begin muscle activation when it’s important to protect healing tissue, especially after shoulder surgery.
Researchers wanted to compare the muscle activation during different AAROM exercises. They divided 11 forward shoulder elevation exercises into 3 types: gravity minimized, upright-assisted, and upright active. 15 healthy subjects performed these exercises in random order while EMG levels were collected in the anterior deltoid, supraspinatus, and infraspinatus. The authors measured maximal activity of these muscles to determine the greatest demand on healing tissue. Each exercise was performed at 30 degrees per second.
During the shoulder pulley exercises, the subjects raised their dominant arm by allowing the non-dominant hand to primarily assist arm elevation. Standing active forward elevation produced the highest maximal levels of muscle activation. The exercise produced an average activation level of 17%, 14%, and 31% MVIC (maximum voluntary isometric contraction) of the supraspinatus, infraspinatus, and anterior deltoid, respectively. Their findings of activation levels during rope-and-pulley exercises were consistent with those of Dockery and colleagues (1998), who found similar activation levels.| Supraspinatus | Infraspinatus | Anterior Deltoid | |
| Gaunt et al. 2010 | 17% | 14% | 31% |
| Dockery et al. 1998 | 18% | 10% | 25% |
Table: %MVIC of muscle activation during shoulder pulley forward elevation AAROM in healthy subjects
The subjects also performed a supine exercise with a Red Thera-Band® resistance band starting with the shoulder flexed to 90°, externally rotated, and elbow straight. They actively moved the arm to 160°, lengthening the band and slowly returning to the starting position. Interestingly, the supine Thera-Band exercise produced less EMG activation than the shoulder pulley exercise at 8%, 13%, and 15% of the supraspinatus, infraspinatus, and anterior deltoid, respectively.
| Supraspinatus | Infraspinatus | Anterior Deltoid | |
| Active Shoulder Elevation in standing | 29% | 21% | 45% |
| Supine Thera-Band 90-160° | 8% | 13% | 15% |
| Shoulder Pulley forward elevation | 17% | 14% | 31% |
| AAROM elevation in standing with bar | 16% | 13% | 30% |
Table: %MVIC of muscle activation during other ROM exercises in healthy subjects (from Gaunt et al. 2010)
The authors found that all gravity-minimized activities including the Thera-Band 90-160° flexion exercises would be appropriate “in the earliest stages of a rehabilitation continuum to regain active motion.” Furthermore, these exercises would be a good ‘first-step’ in progressing patients from passive ROM to active-assisted ROM exercises. The authors also concluded that upright assistive exercises using a shoulder pulley produced low-to-moderate activation levels.
All exercises produced lower EMG activation than active shoulder elevation to 160° in the scapular plane. The authors noted that exercises that protect the supraspinatus and infraspinatus don’t have to be progressed first in gravity-minimized, then to upright active-assisted ROM exercises since low levels of activation (<20%) were seen during those exercises. However, patients who need to protect the deltoid (particularly after open rotator cuff repair) should perform gravity-minimized exercises first, then upright-assisted.
In conclusion, shoulder pulley exercises produce low levels of activation in the rotator cuff (14-17%) and moderate levels in the deltoid (31%). The supine Thera-Band exercise from 90 to 160° produced 8% to 13% rotator cuff activation, and 15% deltoid activation. Clinicians can use this information to make better clinical decisions for exercise prescription in post-operative shoulder patients.
REFERENCE: Gaunt BW, et al. An electromyographic evaluation of subdividing active-assistive shoulder elevation exercises. 2010. Sports Health. 2(5):424-432.
