In 1982, two doctors wrote a paper that changed the way shoulder exercises were done. Dr Jobe and Dr. Moynes studied the movements of baseball pitchers when throwing a ball. They saw that one muscle in the rotator cuff is very important for athletes using a throwing motion. Called the supraspinatus, this muscle moves the arm out away from the body. It also keeps the shoulder joint in the socket when the arm is hanging down at the side. Their research showed which exercises strengthen the supraspinatus muscle.
Since that time, doctors, physical therapists, and athletic trainers have used the “Jobe exercises” to strengthen the rotator cuff. Now, twenty years later, researchers have newer and better technology available. It is possible to retest these exercises and see if they really are the best ones to strengthen the supraspinatus muscle.
In the past, EMG (electromyography) studies were done. Needle electrodes were put into the muscles. These measured the electrical activity of the muscle fibers. The results with EMG were different from study to study. This is because the electrodes change position when the muscle moves. Only a small number of muscle activity could be measured at one time.
Today, MRI (magnetic resonance imaging) is used to measure muscle activity and relaxation. This is a much better measure of muscle function than EMG. Researchers found that two of the three Jobe exercises are still the best in moving the supraspinatus muscle.
The “empty can” exercise is done by lifting the straight arm upward and slightly outward with the thumb down, as though a can were being emptied. The “full can” exercise is similar, only the thumb is up. Thumb up or down, MRI results show these two exercises give the best workout for the supraspinatus muscle.