Refers to the apparent increase in muscle mass shortly after a workout. In some cases it may be used to say that a person is working out, often before an event when taking your shirt off is appropriate. ie. boating
bro: I just fired up the engines, called some girls and threw some beers in the boat. Get your ass out here.
Dude: Give me 30, I need to hit Gold's and throw my dude pads on.