How about a shoulder that's as strong and free of pain as it was at age 18?
When I was that age, I carried around 20 pounds of photo equipment for a job that lasted three years. After that, I carried 20 pounds of textbooks around a large campus for four and a half years. By my early 30s, I had chronic neck and shoulder pain, sometimes severe, sometimes niggling. I took to carrying a backpack instead of a purse to lighten the load on the shoulder.
Besides seeing a chiropractor, which helped a lot, I learned yoga neck stretches from the book Yoga for Americans written in 1959 by Indra Devi. I learned to pop my neck--loudly--at will. Without the exercises, I'd have needed a lot more trips to the chiropractor.
In the past few weeks, without thinking about it, I've been carrying my backpack on my left shoulder--the one that bore the textbooks and the photo equipment for seven and a half years. I haven't had a twinge of pain or fatigue from it. No popping in my neck either, and no real need for the yoga exercises. Possibly, this is because of months of strength training and a wheat-free diet. I don't know of any studies to cite, but I've noted several comments on other blogs from people whose joint pains went away when they gave up wheat. Now, I don't believe these measures would cure someone whose cartilage is gone or tendons are torn. If you have a shoulder injury, you should see a doctor about it. In any case, though, giving up wheat won't hurt you and might bring some relief. I also believe that good muscle tone can help protect you from injury and fatigue.
My canvas and leather backpack has been great, but it's cracked and stained, and I no longer need it to carry my lunch, wallet, sunglasses and a book to work and back. It was time for a change, so today I bought a big silver nylon purse with black patent leather straps and a pink lining. (Sorry, vintage enthusiasts, but a cute little Bakelite pocketbook won't hold my lunch--and I wouldn't want to ruin a vintage treasure forever by spilling salad dressing in it.) The new bag matches my new black sandals and makes me look the way I feel.