IIRC women have to start before men for their records to hold, as otherwise women could gain from the faster men's slip stream. Of course, there are still pace

IIRC women have to start before men for their records to hold, as otherwise women could gain from the faster men's slip stream. Of course, there are still pace makers so even men can take advantage of that, and men can run behind each other and their records would still hold. I think the reasoning is that at least they're running behind/ahead of racers who are competing with them, whereas if women and men started together, the front runners of the women's race would be able to run behind men with whom they are not really competing, and who would thus be less careful about giving them a lift.