Rotator cuff problems are common in the swimming world. You may find as I did, the problem is not the reach out of the water, it is the pull underwater. The way to ease the pressure on the rotator cuff is to make your pull underwater shallower; bend the elbow and pull your hand along closer under your body. Don't forget to stretch the shoulder after you are completely warmed up.
To work on breathing, use a leg float and just do an arm pull and try concentrating on alternating your breathing on each side.
I have to say that this is probably not the way to go. Actually, it certainly is not the way to go. This could relieve any pain that you are having as long as you are not actually pulling quickly under the water. As a "professional" swim coach, this is something that I would not teach anyone to do. If you are pulling with some force this will actually cause some shoulder impingement. To alleviate your pain (and to get faster) you should try pulling with your forearm, as others have suggested, with your fingers pointed towards the bottom. When your hand enters the water some people describe the position your arm should be in as if you are reaching over a barrel. Once you get into that position, you should use your forearm to "pull".
As for breathing every stroke, this is something that you can do ONLY if you are a REALLY good swimmer. Generally, most of us are not. We need to swim a majority of laps breathing to both sides to keep our strokes honest. Many swimmers train while breathing to both sides, then race when breathing to one side. If you continually breath to the same side, you will eventually hurt one shoulder. You can trying one lap breathing only to the right side, then another breathing to the left side. Then you can still breathe every stroke if you wish. This brings me to another point: Generally people who get tired easily in swimming are not spending enough time exhaling. Blowing bubbles is the most important thing in swimming. Breathing every 3rd or 5th stroke will help you exhale slower.
I would also recommend to any swimmer that they take breaks during their swims. When Michael Phelps trains sure he does the occasional 3,000 yards without stopping, but 90% of the time he is doing 25, 50, 100, 200 yards in a row then stopping for 10,20,30 seconds - then he goes again. I see triathletes swim and swim and swim without stopping all of the time. I wonder what they are working on. They get more tired. Their strokes fall apart.....it just gets ugly.
Sorry for the rant, riding my bike is only my hobby. Coaching swimming is my passion (and job!).
