Table of Contents
The problem you have is a movement pattern, based on a muscle being too tight. So the thing to do is first relax the muscle, then drill a new movement pattern. The most effective way to do this isn't all at once in a big three-hour session, but little and often. Try a couple to five times a day for about two to five minutes.
First, Learn To Find It!
Finding your teres major isn't that hard. It's easier if you take your shirt off. Use your fingers to find the base of your scapula, then follow the outside edge of your scapula up until you're touching your arm. Retrace your steps about one to two inches and you're touching your teres major.
Now, Learn To Do Myofascial Release On It!
Myofascial release is a form of massage, one that you can do yourself and that can be very effective on muscles that have gone into spasm and are causing pain or dysfunction. Sometimes, it's enough to simply press on the teres major hard with your fingertips and elevate your arm. The combination of pressure and stretching can make the muscle suddenly "give," springing back to a better length. If you get a loud pop from your actual shoulder joint, the glenohumeral joint, coupled with some pain and a sense of release, you're probably on the right track. Another effective method is to use balls. Personally, I use a baseball, finding tennis balls a little soft and lacrosse balls a little scary, but experiment. Either put the ball in place then lean against a wall, or lie on it, and slowly move your arm through a full range of motion, being careful to make sure that you're not injuring yourself further.
Next, Learn To Stretch It
Again, find a wall. Face it, then turn so your bad shoulder is towards it and you're facing 45° to it. Put your elbow against the wall at shoulder height, put your hand under your arm to monitor scapula position and use the wall to move your forearm downward, trying to get it vertical. Shrug your shoulder up slightly and relax. As you do this, you're extending your teres major as well as the rotator cuff muscles.
Finally, Learn To Relax It
The teres is a postural muscle that tends to tighten when you throw, and the best way to relax it is careful, attentive mobility tower that focusses on rotation and scapula control. But you do that on a weekly basis anyway right? Ahem. Well, if not, now's a good time to start!
If you like whet you've read, or you want to pull me up ono something, get in touch in the comments section.