I have played upright now for a few years, but besides a few shows in high school, it has more or less just been a side project of mine. Lately though I have been taking it a little more serious. Ive taken lessons of and on for years and I think that I have a pretty good understanding of the technique but lately Ive noticed that I get tired very quick. After only ten minutes of playing my shoulders hurt and I have to stop. I know that you guys havent seen me play so this might be a hard question to answer but is there anything kind of obvious that you know of that might cause this fatigue? I dont really notice any pain; I just stiffen up in the shoulders and back. Also, I noticed that it happens a lot worse when I stand, and not as much so when I sit. And if there are any exercises that you know of to build up endurance so that I could play a half-hour to an hour at a time that would be great. Right now Im just practicing playing scales with a metronome nonstop to try and get my strength up. Thank you for any help.