How do we know these girls are in such good shape? Well, we looked, obviously. But also, they seem to dig working out, which is good for, you know, uh, heart rate and stuff. Also their butts.

We've got GuySpeed favorites Jen Selter, Michelle Jenneke and April O'Neil here, plus one girl in a pink thong doing some sort of stairs routine. Anyway, there are three marvelous GIFs of her doing whatever that is.