I sometimes feel REALLY tense in my arms and I'm pretty much playing with bricks. It's not a problem when it's just one time through, but practicing it, it's trouble. sometimes playing it just once is a problem. For instance when i was playing the Black Key etude, I noticed I got tense a little after the recap. It wasn't a problem because I can release tension at breaks such as that high note and then the two quarter notes. but some pieces like the Ocean etude don't have "breaks." It's just perpetual motion. I can release some tension in the recap but not all. The three octave arpeggios don't add much tension, but the two octave and four octave arpeggios do.
All in all, how do I get my endurance up???