Well at the ripe young age of 41 I'm a seething bag of niggling injuries old and new. I have occasional rotator cuff problems, shoulder problems, neck problems, lower back problems, knee problems, tennis elbow in one arm and golfer's elbow in the other. Just been through the wars I guess. I just do what I can in the way of exercises and cope with it. I think some of my tennis elbow/tendon problems came from playing guitar in the classical position because when I play like that now my arm hurts like hell.
Some suggestions:
1) Play with wrist supports on. I have a set of these, they are excellent:
http://www.newgrip.com/guitar.html - probably a little overpriced, but they're better than the ones I've tried from drugstores.
2) Get a Thera-band FlexBar:
http://www.thera-band.com...php?ProductID=20 - there's an exercise you can do with it for tennis elbow that's proven to work. It's also good for general arm/wrist strengthening and tendon problems. Comes with a little booklet with loads of exercises in. They come in different thicknesses - best to start with the medium light one (red) and work your way up to the thicker one (blue). It's best to start the exercises lightly and when the pain has died down a bit.
3) Take bromelain and turmeric capsules. Now Foods does a combined capsule - they work best when you take them together. Bromelain and turmeric reduce swelling and heal tendons. They really do work. Another great one for tendon problems is astaxanthin, a very powerful antioxident (which also provides your skin with some UV protection). Look them up online and see what you think.
I used to be able to play for 6 hours straight without a single twinge. Guess I'll not be doing that anymore, lol! It's probably for the best anyway, I have other things to be getting along with