First turn on Kryptonite (by 3 Doors Down), now stand in front of the mirror, feet are shoulder apart or closer, now moving your knees back & forth just like you would bicycling slow pace but with the beat and then slowly increase it as fast as you can (bend your knees and have good straight up posture so that you don't hurt yourself). Now the trick is to keep your feet flat on the ground, pumping your knees, let your hips move, but the upper half of your body from the chest up should be still just as a desk clerk (or bank clerk).
You pass the challenge if you could have the bottom half move with the beat full time, make sure you are still breathing, smiling and still as if nothing is going on if someone just look at you on the top half.
If you want more, try to walk around with, moving forward for awhile and then back. Keep it graceful! Enjoy!
Note: try it at your own risk, don't do it if you're too full Pick your favorite up beat music and don't hurt yourself. This exercise should not cause your pain in any way, if it doesn't check your posture or just stop.