HIM During "That Time of the Month"

Obviously every woman is different, but both theoretically and on average, women do actually do better on those days.

You're not likely going to feel great to start out with, or possibly even during, but chances are those sensations will clear up as you race, but even if you continue FEELING sub-par, it's not likely to affect your performance (as you can see, the likelihood is the opposite).

I'm assuming because of nix Pill that this can't be done either, but it's a far more temporary state (this excerpt is from Livestrong):

Use Natural Progesterone Cream

Progesterone is the hormone that rises during the first half of your cycle, then decreases during the second half. The dip in progesterone signals your period to start. If you just need to buy yourself a few days, you can keep your progesterone levels up with natural progesterone cream. NPC is available at health food stores; different manufacturers make creams with different concentrations. Starting at ovulation, or at the midpoint of your cycle, apply one-fourth of a teaspoon of the cream two times per day, according to John R. Lee, M.D., of the International Center for Nutritional Research. When you are ready for your period, stop using the cream. The withdrawal of progesterone will cause your period to start.

Increased physical activity the few days before may do it, too, but not exactly a recipe for a smooth taper and getting you to the start line fresh!

Some people think cutting out all spice (even white pepper or mustard, anything remotely hot) at mid-cycle will prolong the second half, thereby delaying menstruation. Alternately, if you want to fire up during mid-cycle, may bring your menstruation on earlier, most effective if started a few cycles ahead.

Various levels of consumption of soy, lavender (not sure about that one, don't quote me on it), shepherd's purse herb, and/or a ton of ibuprofen (not recommended) plus high levels of the B-vitamins several days before are thought to postpone menstruation.

However, going au naturel (so to speak, not literally ) seems like it'd be best for your performance anyway.

In any case, GO IRONHOBBIT GO!