Planks are effective on their own, but add a stability ball in the mix and you'll really feel the burn in this core and butt-toning move.
- Lie on an exercise ball under your belly and walk your hands out until the ball is under your shins. Your hands should be directly under your shoulders.
- Draw your navel toward your spine to engage your abs and stabilize your torso.
- Lift your left leg up, squeezing your glute, then slowly lower your leg back onto the ball. Switch sides and lift the right leg keeping your pelvis square. This counts as one repetition. Complete three sets of 10 to 12 reps on each side.