Tired Muscles

I've been practicing Chopin Étude 10 no 2 A minor and my right arm gets tired. I think it's because 3rd 4th and 5th fingers aren't strong enough. Does that burn/tired feeling mean that I'm gaining strength? It's the same feeling I get after lifting weights but I know some people say that feeling is not good thing. Thanks!

You do need to develop stregth in those fingers. But don't do it by "body building," by stressing them... Find the agile way - by making the inner chords of the right hand louder, clearer, more perceptible, and also by snapping off them which naturally makes your wrist go up and to the right - the very direction you need to feel more agile without too much extra effort... AFF