I climb everything from 5 grades below my current level to one grade above. I have found that consciously maintaining good technique on the hard routes helps me out a lot. I don't believe in "redpointing," so I usually don't try to force myself up a really hard route that I'm having trouble on. That is how you get injured.

The soreness I get after climbing is the same kind of soreness I used to get during the first two weeks of a weight lifting routine. It is not tendon damage or severe muscle damage because it doesn't last more than a day.