It’s a muscle and bone mass thing coupled with training.
A 100 lb man and a 100 lb woman fighting would not be a fair fight any more than me (230lbs) fighting a 230 lb black bear would be a fair fight. I’d almost certainly get my butt whipped, and then eaten. :)
I don’t know about that. Like I said, Bruce Lee and Jackie Chan managed to beat up people twice their muscle-mass and bone density all the time, and those guys are practically toothpicks (compare their muscle mass compared to, say, Schwartzenegger at his peak).
Besides, I definitely recall seeing a car commercial where a kid not only wrestled with a bear, but was actually WINNING. It’s this ad, in fact, 20-25 seconds in:
So it’s definitely within the realm of possibility.