Pitchers are weird people, mostly because of the physical act of throwing. The motion is so violent and powerful that it throws a pitcher’s body out of whack and causes major asymmetries in strength, size, flexibility and range of motion, bone structure, etc.
One major adaptation of the pitcher is in shoulder range of motion (ROM). Pitchers have incredible, otherworldly external rotation. The average person couldn’t dream of contorting his arm in such a way.

My buddy Andrew Germuth showing off his external rotation
And what price do we pitchers pay for enjoying such lavish external rotation? You guessed it! A tight rotator cuff and a subsequent deficiency of internal rotation. (there is always a catch!)
So what? Does it matter if a pitcher has poor shoulder range of motion internally?
The answer to this question is unequivocally “yes.” Any trainer or physical therapist will tell you that a lack of ROM in any joint is pathological and indicative of underlying problems. Normal ROM should exist in all one’s joints, and if not, there is a probably a problem as to why. In many populations these imbalances in flexibility might not impair day-to-day functioning, but for athletes and especially pitchers, inflexibility poses major problems.
Dr. Craig Morgan and colleagues are researching the link between elbow pain (up to and including full blown ligament tears requiring Tommy John surgery) and internal rotation. What he is finding (as he found in me) is that a huge amount of pitchers coming to him have significant GIRD (glenohumeral internal rotation deficiency), and once that GIRD is reduced to an amount within 20 degrees of the internal rotation of the non-throwing shoulder, the pitchers very often return to throwing without pain. Internal rotation deficits are caused by posterior shoulder capsule tightness, which can be alleviated using the sleeper stretch. Restore your internal rotation ROM and you will be throwing healthier and harder.
The Sleeper Stretch
The basic form is as follows: lay on your hip with knees bent, with ankles in line with your spine. Prop your head (or don’t if you like being uncomfortable) under a towel or pillow, your glove or whatever. Extend your throwing arm out in front of you at 90°. Keep your chest out and don’t lean back.

Sleeper Stretch Starting Position
Next you need to pinch your shoulder blades together, hard, and hold them that way throughout the stretch. This is crucial, and the stretch is useless without pinched blades because your shoulder will be in improper position.

The WRONG way - Blades are not pinched, shoulders misaligned

The CORRECT way - blades pinched, shoulders in better alignment
I held a pencil in the middle of my back for effect – think about holding something there while you perform the stretch.
Once your blades are held together, take your other hand and GENTLY push your arm toward the ground. Don’t force it, just give it enough of a push to feel a stretch. I have to stretch mine 3 times daily to keep it loose, and from the beginning it will take a few weeks to really loosen up. Forcing it won’t help, it will just cause more problems.

A good sleeper stretch
Notice how much internal rotation I have in the above picture: about 45 degrees. Once I go through this I gain about 10° more, but that’s it. Watch what happens when I don’pinch and hold my blades together:

The WRONG way. If you look like this, your shoulder blades are not pinched
If you see someone at the field doing the sleeper with their palm almost on the ground, correct them, because they are doing it wrongly. Try it the right and wrong way so you feel the difference. In proper position with blades pinched, if you have 45 degrees like I do, then you are looking great. When I go in for checkups I measure symmetrical to my left. Everyone has a different setpoint, but no one can put their palm to the floor. It looks about the same, though, which is why players so often do it incorrectly.
Variations and Reps
So now you’ve mastered the form in the 90° position. The three positions from which you will stretch are 90°, 70°, and 110° from your shoulder to your body. Stretch your arm for 3 sets of 30 seconds at each position. Even at 70 and 110, keep a 90° angle with your forearm and upper arm.

Correct angle between forearm and upper arm

INCORRECT angle between forearm and upper arm

Proper stretch at 70 degrees from body

Proper stretch at 110 degrees from body
The orientation of muscle fibers in your rotator cuff varies, which is why stretching three positions is recommended.
So do your sleepers daily, and do them correctly. If you do, you’ll be taking a huge step toward both keeping yourself injury-free, and picking up some MPHs. Flexibility plays a big role in velocity, and I picked up 3-4 from increasing my ROM in my shoulder and in my hips (which I will discuss in a later post).

Great job, very clear explication of proper form and benefit and checking for bilateral symmetry in the ROM. Sets and reps, thorough and understandable. Shoulder blades together. Good form equals good payback. Thanks much, gene
[...] are many sites that discuss the sleeper stretch. But, in my opinion, Dan Blewett has by far the best and most thorough description of how to safely and effectively stretch the [...]