I smoke pot and excise more often than just smoke pot. I play DDR alot and lift weights too. Go to the odd tae kwon do class too (not super baked though). I havn't notcied any bad effects at all. Only thing I find different is I can do more pushups, play longer, whatever it is. For me, being high takes the part of the mind that says 'ok I want to give up now becuase its getting hard' and tells it to fuck off. I think it gives me a better workout.

Either way, I would figure that exercising when your high is better than not exercising at all, so if the only time you feel like doing it is when your high, do it.

Edit: maybe don't do it if you have high blood pressure and stuff. I guess the key is you are worried, do it in small amounts and get used to it. The most important thing is to listen to your body, it'll tell you what hurts it and what helps it.