Magnetic Resonance Imaging Evaluation of Muscle Usage Associated With Three Exercises for Rotator Cuff Rehabilitation.

Magnetic Resonance Imaging Evaluation of Muscle Usage Associated With Three Exercises for Rotator Cuff Rehabilitation Horrigan JM, Shellock FG, Mink JH, Deutsch AL (Horrigan Sports Chiropractic; University of Southern California; Tower Imaging, Los Angeles, Calif), Med Sci Sports Exerc. 1999;31:1361-1366.

In recent years, researchers have begun to use magnetic resonance imaging (MRI) to analyze skeletal muscle immediately after exercise. An increase in signal intensity from specific muscles indicates that these muscles are used during a given exercise or activity. This study analyzed the MRI changes seen with 3 common exercises used in rotator cuff rehabilitation. Five healthy subjects (3 men, 2 women, mean age = 31.4 years) without shoulder pathology were studied using MRI before and after performing the following exercises: scaption (abduction in the plane of the scapula) with internal rotation, side-lying abduction, and the military press. The exercises were performed in 4 sets of 15 repetitions interrupted by a 1-minute rest period. Depending on the exercise, resistance varied from 3-lb dumbbells to 25% of the subject's body weight.

Magnetic resonance imaging studies were performed before exercise and within 60 seconds after each exercise. The measure of interest was signal intensity at approximately 20 sites on the each of the muscles studied (ie, supraspinatus, infraspinatus, teres minor, subscapularis, deltoid, trapezius muscles). An ANOVA was used to compare the resting and postexercise signal intensities at each muscle for each of the 3 exercises.

Side-lying abduction was found to have the greatest statistically significant increase in signal intensity for the supraspinatus, deltoid, infraspinatus, and subscapularis muscles, whereas it produced the least change in the trapezius muscle. Scaption with internal rotation demonstrated the second highest increase in all muscles except the deltoid, where it produced the least change. The military press exercise was found to produce the highest increase in the trapezius muscle, the second highest increase in the deltoid, and the least increase in supraspinatus and infraspinatus muscles. No exercise produced an increased signal intensity at the teres minor muscle.

The authors concluded that the increased signal intensity reflected an increase in muscle water content because of the production of lactate and other metabolites. They also noted that the scaption with internal rotation exercise was reported by some subjects to cause symptoms of impingement, and, as a result, the researchers argued that it should not be used for rehabilitation. They further recommended the sidelying abduction exercise as the best overall exercise for increasing the activity of the rotator cuff muscles.

Anne K Swisher West Virginia University Morgantown, WVa