I have a very heavy flow as well, and have noticed that when I am actively exercising, my flow is even heavier during that period of activity.
However, like the other posters, I don't change my work-out at all, but especially in the few days leading up to it, my energy level can be so low that I put in a less-than-stellar work-out. Nevertheless, I try to push myself to power through it and just get the work-out in to maintain my routine and get whatever benefit I can from it. My reason for this (and I am not saying that you are similar to me) is that I have such a catalog of excuses (low-sleep night, my knee is bothering me, the perfectionist "I don't do this perfectly so why do it at all?" nag, etc.) that I just need to get my butt in the gym or in the glorious outside and do. something.
Warning, this may be TMI, but I also love those AF after-work-out showers the most ever. All the sweat and blood being expelled from my body is cathartic for me.
Trainer boy challenge (07/11-09/11):