Foot-to-Foot Bicycle Crunch

Pressing and resisting against each other's feet while doing this supereffective crunch makes your abs work harder.

With legs bent and feet flat on the ground, lie on your back, toe-to-toe with your partner. Press the soles of your feet against your partner's feet and lift them off the ground, so thighs are perpendicular and calves are parallel to the ground.

Contract your ab muscles and lift your head and shoulders off the ground as far as comfortably possible.

As you lift, pull your right knee toward your chest, extend your left leg, and twist your torso to bring your left elbow toward your right knee. (Your partner should do the same, so you are moving in sync and pressing against each other's soles at all times.) Hold for a second, then lower and repeat to the opposite side; that's one rep.