After listening to Hard Candy a few more times (and "Heartbeat" a bunch more), I have to refine my review of the album just slightly: After hearing several references to dance floors, like, "on any given night, catch me on the floor, working up a sweat..."
Really, Madonna? At nearly 50, with two children, you're still out in the club, working up a sweat?
First of all, the amount of Human Growth Hormone you've taken to rock your body (leaving your face with that hard look) would directly affect how easily you sweat, and the amount you sweat.
Secondly... I've been out dancing in the past year... didn't see you.
(But I still like the song.)