You know, we just have to know our limit, althoiugh with proper warm up techniques we can really damage our fingers very easily if we don't know when to quit. A friend of mine was playing very hard on stage and he damaged his left pinky really bad, it wasn't broken but as a result its never been the same again. He used to clench his hands against the fret board very tight, you have to know how to take on your favorite licks with just enough ease, even if you are in the moment on stage feeling the power from the audience and your instrument. Ide personally recomemd that practice sessions should only last two hrs at a time, giving your joints enough time to rest. Believe me, I know how easy it is to get carried away.

-Joseph, :).