Originally Posted by f4rrest

Mine also hurt on catch phase (regular crawl stroke, not TI) and I was exacerbating a biceps tendonitis issue (yes, it's part of the shoulder), but I have been training weights all my life, so shoulders are well developed. The injury likely started with years of overuse in the gym and just got worse swimming.

PT said to totally stop weights for 6 weeks! Only did a few seemingly easy exercises with bands and a 1 lb weight.
With that in mind, assuming you have a similar injury, starting a weight regimen seems like the wrong thing to do unless you see a doctor or PT first. In fact, it will likely cause further muscle imbalance, since many people at the gym only train their favorite muscles (biceps, presses, etc.) and neglect the stabilizing muscles in the shoulders.

Here's what my PT had me do to correct some inherent muscle imbalances (some of which were caused by normal weight training):

In all the below, keep shoulders down and back with shoulder blades squeezed together, almost touching each other (especially exercise 3 and 4!). Do not do these quickly. Twice a week is ideal.

1. "pulldown to front": band attached top of door, stand directly facing door, start with arm extended toward top of door and pull with straight arm (elbow locked) down to side. 15-20 reps. Switch arms.

2. "pulldown to side": band attached top of door, stand with left side facing door, start with left arm extended to your side toward top of door and pull down with straight arm (elbow locked) to left side. 15-20 reps. Switch sides.

3. "inward rotations": band attached waist height to door, stand with left side facing door, upper arm locked against side and elbow bent 90 degrees (away from you), left forearm starts from left and rotates inward across your belly, keeping elbow bent, don't let your elbow move away. You'll feel it in frontal shoulder and chest. 15-20 reps. switch arms.

4. "outward rotations": band attached waist height to door, left side facing door, upper arm locked against side and right elbow bent 90 degrees, right forearm starts from left (already crossed over belly) and rotates arm away from your body out to your right. You'll feel it in back of shoulder. 15-20 reps. switch arms.

5. "sixes": using small 1lb weight in left hand. Lie face-down on bench. If you don't have a bench, you can get into hands and knees position. Start position is with upper arm extended out to your left side, elbow locked at 90 degrees, forearm hanging down from elbow towards floor. Keeping your elbow and upper arm in same location, VERY slowly rotate the weight up until your forearm is parallel to the floor. Hold it for a bit, and then rotate it back down again.
(You should count "one-one-thousand, two-one-thousand..." up until "six-one-thousand" while rotating up. Again while holding, and again while rotating down). Do six reps. It burns! You'll feel it in back of shoulder and upper back. Wonder why she called them sixes?

Over time I was able to work normal weight exercises back into my routine, but I still always start with the rotator cuff work on the bands as a warm up. It was surprising how it actually balanced my overall physique as well.

These are the only isolation exercises i do (no more bicep curls or bench press, etc. as wolfchild says). A few weeks after you no longer have any shoulder pain, add some compound exercises back into your routine. Those bands can be used for standing rows, etc. Be REALLY careful about doing anything that presses over your head.

Oh, and please see a PT or doctor, in case your injury is different.

Forgot to add: the PT was able to stretch these little oddball muscles under my armpits way deep inside the shoulder joint to relieve some pain. It's something you can't do on your own. Go see one.