The cultivation of piano playing as a competitive, athletic pursuit, an obstacle course requiring stamina and endurance, is bad for mind, body and music.
What I always heard is that if your way of playing a piece causes any pain or discomfort whatsoever, even momentarily, even in very hard pieces, you are playing wrong. Usually pain and discomfort are a result of too much tension in the body, and you have to work on playing everything in as relaxed a manner as possible.
With the fast repeated octaves in Scriabin, it should help to focus on one large arm movement for every group of octaves, so that the fast, small wrist movements needed for the individual octaves become sort of 'after-bounces' or recoils.
I think 90% of the practice time should be used for non-power playing: piano or maximum mezzo forte. Also go from slower to fast but still in p to mf. 10% can be used for maximum power/tempo. By doing so you will not be exhausted or turn stiff.