Ninja Warrior / Sasuke
Got a wiki article you can read there to find out more. As for the G4 contest thing, this is the first time I heard about it (haven't watched since summer vacation started), but I doubt anyone here could do it. Being an athlete is simply not enough because Ninja Warrior obstacles demands way more than a decathlon does.
As for your other question, there are women that does the men course just not a lot as most of them participates in the woman version of Sasuke. I believe the only women that are in the men's division are the female's division's champ and 2nd place; and also that "tranny" who used to be a man but is now a woman.