The isometric split squat is a simple technique to build serious lower-body muscle. It increases the time your glutes, hamstrings, and quads are under tension at the most difficult portion of the move--the bottom. But if you really want to up the ante, try adding a dynamic kettlebell to the mix. (Build muscle and fry fat all over with this killer Total-Body Kettlebell Workout.)

"The kettlebell over-and-under pass forces your core and lower-body muscles to stabilize as the weight travels around your front leg," says BJ Gaddour, C.S.C.S., creator of the Bodyweight Muscle Burners DVD. "The only things that should be moving are the bell and your arms. Your core and front leg must stay engaged the entire time to keep your body stationary against the pull of the weight." And because this exercise hammers some of your body's biggest muscles, you'll burn a ton of fat, too.

Ready to try it? Watch the video to learn how to perform the kettlebell over under with perfect form.

Which moves do fitness experts hate? Read 5 Exercises That Make Trainers Cringe.

Story continues below