If you *need* it to get yourself composed enough to go to the gym, then by all means take it. It will help you improve your physique.
If you're already training hard and are just now thinking about incorporating it into your pre-workout plan, I'd think twice. On a small dose, it's not going to really set you back much, but it also won't allow you to reach your potential. I'd only really say that you shouldn't do it if you're training really hard for something (bodybuilding, powerlifting, marathon, etc.)
For the average person just trying to stay in shape and be healthy, if Xanax helps you stay sane in your routine, I don't see it being a problem.
i think that if you are used to xanax like me, who takes about 8 mg a day can work out just fine..... i need xanax to get through the day....i have severe anxiety from past drug abuse, (MDMA, LSD(which i still use) but its better if you are prescribed and used to it. I have done it with no problem. But ive been on 4 bars a day for 14 years. So there really is no point to take if your not dependent on it. I am also prescribed to adderall which i have been for the same amount of time and that definately helps me work out....but i have to take a bar..... but i usually break both in half.... just to be safe on the heart due to the upper speeding up your Central Nervous System and the xanax slowing it down. So be careful. Eat bars when you arent drinking and need to ask a girl on a date or something. Or before court. Thats best.