f(x)‘s Sulli and Amber revealed how they maintain their toned figures and the best part is that it’s absolutely free!

On the August 17 broadcast of ‘Star King‘, the duo demonstrated how they lose weight by inflating a plastic bag and kicking it around in various ways so it doesn’t drop to the floor. Amber also got into a hilarious mishap when her shoe fell off while trying to play the game.

Source: allkpop