You'd want to ensure that you have adequate range of motion for the golf swing. It's not clear which "extreme angle" of the golf swing gives you the "pop." Key movements would include internal and external rotation of the shoulder, but in your case (and as a fellow lefthander who plays righty), you also need good flexibility of the posterior capsule of the left shoulder.
Sounds as if you might have some rotator cuff irritation/degeneration due to "impingement." You will want to ensure that your scapula (shoulder blade) is free to move and help make your shoulder successful. The shoulder blade very much depends on the muscles attached to it, as it's only direct connection to the skeleton is to the sternum through the collarbone. [And, if we really want to clear you, we'd check the mobility of your upper thoracic spine] So, we need adequate flexibility of the chest muscles, lats, upper traps, and the muscles between the shoulder blades.
The exercises you were given sound like traditional shoulder rehab exercises. Um... you might want to try exercises that look and smell a little more like golf. What does your left arm do during a golf swing? Try some exercises that replicate those movements, particularly on the loading aspect (i.e. backswing) and the deceleration aspect (follow-through).
One last tip (and possibly the biggest one) - is your buttock and hips helping your left shoulder to be successful? This is a serious question.
Hybrid Mode
