http://www.egscomics.com/d/20020420.html
So how much power can they use before Greg's insurance ducks out? I'm guessing... 60%. That's still enough to have moderately impressive fights, but still low enough that damage is relatively rare, and when it does occur it's nothing some plaster couldn't fix. Any more than that and you wind up with students (and instructors, really) becoming People of Mass Destruction, and no sane insurance company would be willing to cover that amount of possible collateral damage.
And while I'll probably get hammered for paying attention to this, but is it just me or does Sarah seem a lot more well endowed back then than she is these days. You could probably just attribute it to Dan improving his artwork and changing style and all that, but Sarah almost looks as big as Nanase here.