Weak lats are one of the main reasons for shoulder impingements, IMHO. The lats span all the way from the back of the armpit, to the mid-spine down to the lower back—basically the bottom half of your back. They tend to be tight and weak in most adults I’ve encountered. For frozen shoulder, the lats get in this dysfunctional relationship with the pec minor and teres minor. Essentially, having your arms bent in front of you like a T-Rex all day, shortens your pec minor and biceps muscles. Another, very small muscle of the rotator cuff, the teres minor, helps support this pattern through the back of the armpit. The lat, on top of the teres, then becomes stuck in a holding pattern to have your back in this 21st century posture.
Hands down, the best way to release the muscles and fascia of your lateral line re:shoulder impingement is to use a cupping set. Here’s the one I own from Amazon. Use those cups (you can also do a couple pumps and drag along your skin, just make sure to have some coconut oil down first) on your triceps, upper traps, lats and even IT band.
Once you get all that loosened up, this video includes some lateral line stretches. We go over different ways to stretch the lats by changing the position of your arms. Then stretch the lateral aspect of the torso. And then take that down to the IT band. Pay attention if you have a tendency to keep one knee bent ever-so-slightly during this IT stretch—is it on the same side you have the shoulder pain? If you just stand without thinking and look down, is that same foot outside further away from your centerline (think about drawing a line straight down from your zipper)? Or, is it the other leg? These imbalances at the hip can affect whether or not your shoulder feels like it needs to help that side get forward in gait (how you walk) and can be another layer of problem-solving frozen shoulder. I also include a link to some calf and hamstring stretches in this video, as they also encompass the lateral fascial chain.
We then move to activating the lateral hip stabilizers, read: your balance muscles. You want to feel the bulk of this action at the gluteus medius aka the love handle area. Next up is activating the lat itself. The primary action of this muscle is to turn the arm inward and pull it to your side. I demonstrate a way to do this with a theraband. Things to watch out for in this exercise are to make sure that your wrist is in alignment with your forearm and to slowly let the arm release away from your torso so you’re working the lat in a full-range. The last set of muscles we activate in this video are the triceps—I call this my trifecta of triceps. Expect to be a bit sore the next day even if you don’t use any weights.
The content in this video is suuuper important for understanding how a shoulder impingement happens and how to gradually start shifting those tectonic plates of your shoulders and back to correct it at home and for the long haul.