I recently found out that- wearing Thongs or G-strings can help tone up or should i say FIRM up your ass. Wear it out, or during your workout or even during your sexy time (kinks up the session!).
Your mind will automatically tell your butt muscles to squeeze/clench together, and by doing this on a daily basis it can help get you that firm bumbum! :D
Try it!
Here's a better explanation of it. Clickety Clicky!
