Here's a quiz: Is it worse for a girl to tear her ACL playing soccer or for a boy to get multiple concussions playing football? Or what about a 9-year-old girl driving a go-cart head-on into a concrete wall, smacking her body into the steering column, hitting her head on...

British marathoner Paula Radcliffe's victory in last Sunday's NYC Marathon raises an intriguing idea: Might pregnancy be a boon to female athletes?

The notion is compelling not just because it might be physiologically true, but because it challenges the most basic beliefs about women's bodies, namely that the very...