Don't know if it is mentioned here, but I use the swiss ball for glutes and a 10kg plate. I lie on the floor with my feet over the swiss ball, and a 10kg plate on my ab's (you may need heavier) and I dig my heels into the ball and lift my butt off the ground, hold for a count of five seconds and then lower back to the ground slowly. Repeat 14 more times and then rest a minute and do two more sets. It damn well hurts after a while I know that much.