A recent workout brought up a few questions on the validity of the shoulder exercise, the empty can. The empty can has long been a staple in physical therapy circles when it comes to shoulder rehabilitation. Dr Frank Jobe, a well known shoulder specialist, was the first the come up with this exercise. Since then it has become widely known as an isolation execise for the supraspinatus, even though in truth it is not.
According to a study by Mike Reinold, the EMG activity of the supraspinatus in the empty can (thumbs down) vs. the full can (thumbs up) is the same. The difference lies in the activity of the deltoid. The empty can produces high levels of activity in the middle deltoid when compared to the full can. Why is this a problem? The strong pull of the deltoid pulls the head of the humerus superiorly. It overpowers the supraspinatus and rotator cuff muscles that act to depress and stabilize the head of the humerus. It basically creates forced impingement. Not a good thing for an athlete!
The full can (thumbs up) offers the same benefits for the supraspinatus but produces much less surrounding musculature activity in the deltoid. This allows the humerus to stay nice and comfy in the glenoid fossa in a neutral position. As well, by not forcefully internally rotating the humerus, we don’t re-create impingement in the sub-acromial space. Along with internally rotating an abducted arm we can also get scapular protraction, and anterior tilt. The combination decreases the sub-acromial space resulting in. . .you guessed it, more possiblity for impingement.
In my opinion the empty can shouldn’t even be an considered when programming training for the shoulder. I can’t do it due to the pain it creates, and now we have evidence that the full can produces the same effect without creating possible impingement.
Mike’s study of the full can vs. empty can exercise can be found HERE.