Most shoulder injuries are caused by insufficient development of the muscles at the back of the shoulder joint. The most vulnerable shoulder muscle of all is the supraspinatus. In 2007 sports scientists at Massachusetts General Hospital in the US worked out which exercise can help strengthen this muscle group specifically - and thus reduce the chance of shoulder injury.
SupraspinatusThe supraspinatus stabilises the shoulder joint in nearly all movements made by the upper body. Although the muscle is located at the back of your upper body, it is still also involved in bench presses or the shoulder press for example.
StudyThree exercises that physiotherapists and trainers use to help shoulder muscles better withstand injury are the full can [first photo], the empty can [second photo] and the prone full can [third photo].
The researchers got 22 subjects to perform the exercises, and used electrodes to monitor the activity of the subjects' rear and middle delts and the supraspinatus.
ResultsThe prone full can, or reverse fly as it's also called, turned out to be the best overall exercise for the muscles at the rear of the shoulder joint.
ConclusionIf you're looking for an isolation exercise specifically for the vulnerable supraspinatus, then you're best off doing the full-can.
Strength athletes who want to protect their shoulders against injury will do the preventive exercises at the end of their workout. They'll have already trained their delts enough, but not the supraspinatus. The full can stimulates the supraspinatus as much as the other exercises do, but gives the delts rest.