I have struggled on and off with these problems since college. I am a percussionist as a hobby/side-job, and I got my degree in percussion performance. As a result, I did a LOT of drumming around that age. Typing has also aggravated the problem. For many years the problem went away. It returned briefly for a few months, but now I have figured out how to beat it.
The RSI problems have returned twice, both when I was consuming lots of raw dairy plus bone meal. However, as soon as I started taking magnesium supplements this time, it went away.
Obviously, RSIs are an inflammation response. Different people have different amounts of natural inflammation response, so not everybody will get them to the same degree. However, for those of us who are prone, a solution has to exist. I believe a great deal of the inflammation response is actually to calcium crystals in the tendons, etc.. Calcium deposits easily in the body and has a very spiky surface. As a result, it tends to cause damage to the inside of the arteries, leading to blocked arteries. Anyone who has ever been cut by a sharp oyster shell knows how sharp and spiky calcium tends to be.
So how do we beat the problem?
1. Magnesium. It's something most people are deficient in, and it's calcium's antagonist in the body. I supplement with it from time to time, but there are foods that are rich in it.
2. Vitamin D, whether from Sun, fatty fish, or supplements. It moves calcium where it's supposed to go in the body.
3. Correct posture and movement, like the Gokhale Method. This won't completely solve the problem, but it helps, and it's generally useful for any physical activity.
I think another reason that calcium causes RSIs is because it's used by the body to contract the muscles. Magnesium is used for the opposite, and if your balance is too far toward calcium, those muscles in the affected areas can never fully relax and recover.