1) Piano students often have difficulty differentiating between muscle and tendon pain.
I completely agree with you. However, if you CAN differentiate between the two, then you would know when you're on safe ground - muscle pain is usually not a problem, as long as you're not overusing the muscles.
2) One of the objectives of the Chopin etudes is not to build up endurance or muscles, but to learn how to play them in a way that you do not get tired.
I can only agree partially with you. That is certainly one of the objectives for all pieces, but it does not alway happen. Also, one of the ways to play so that you don't get tired is to build up more muscles or endurance. (or stamina. whatever you want to call it). There is no way to play op. 10 no. 2 and not get tired in the middle, unless you've practiced a lot, and whether you get muscle pain or not the simple fact that you have practiced it means that you have built up endurance. There is not a single person in this world who can pick up this etude and play it, and if there is, then that person already HAS the endurance. Isn't that what practicing is ultimately?
I am not trying to be argumentative. What I just said is fundamental to my own approach to playing. Please let me know what you think.
I am also not trying to be argumentative, because I think we are saying similar things, but in different ways, and I take it slightly further than you do. The simple fact that you practice, and after you practice you can play faster and more accurately (of course that's only one of the effects) means that you are building up endurance and stamina. I'm just trying to point out that if you get muscle pain while you're doing it you don't have to stop IMMEDIATELY, because it's muscle pain. But if you get tendon pains you MUST stop, and massage it, because tendonitis is not something to be played around with

Cziffra, If you have tendonitis, you would have problems (in other words, pain) rotating a joint, whichever joint you have tendonitis in. Things to look out for when practicing: tightness in your lower half of your arms (hold your arms horizontally in playing piano position, and the muscles below your bones is what I'm talking about). Tightness above is usually ok, because of the group of muscles directly related to your fingers. The muscles under is related to your entire hand, and there are several tendons in the middle of it. If you get tightness there, stop immediately and stretch your hand up, pulling the lower tendons straight, and do that for a while. it'll hurt when you stretch but at least you're less likely to get tendonitis that way.
Also, generally it is good to stretch your hands before you play. I stretch mine almost constantly whenever I'm not doing anything else with them. Between fingers, wrist up and down, elbows, arms, etc.
have fun practicing:P
mt