Lie on your back with your arms along your sides and raise both legs together to about 45 degrees. Keeping your legs straight and glued to each other, draw slow, even circles in the air with your feet, first in one direction, then the other. Your legs are just the pencil - your abs do the drawing by keeping your lower back pressed into the floor the whole time.

Works: abs, obliques, hip flexors, quads

Breathing: Steady and rhythmic, in time with the circles - don't hold your breath as the set gets harder.

Common Mistakes: Letting the lower back arch off the floor, bending the knees as fatigue sets in, and rushing through tiny fast circles instead of drawing slow controlled ones.

Make Easier: Tuck your hands under your hips for support, draw smaller circles, or keep a slight bend in the knees. Flutter Kicks are a good place to build up the raised-leg endurance first.

Make Harder: Lower your legs closer to the floor and draw bigger circles, or move on to Windshield Wipers for a bigger rotational challenge.