Hi! I am Martica Heaner, Exercise Physiologist and Certified Personal Trainer. Prevention's ultimate ab workout includes lab tested moves that are twice as powerful as crunches. All you need is a Stability ball to get your firmest midsection ever.

To get the most out of your workout, add two minutes of Cardio Intervals, like marching or jogging in place in-between each move. Let's get ready to roll. The Skier works all your core muscles, especially your oblique which stands in your waist. Start by kneeling in front of the ball, lie on top of it, then walk your hands forward, stopping when your shoulders are right above your hands. Your thighs are resting on the top of a ball, from here tightening your abs and draw your knees in towards your left shoulder, so your hips are rotating.

Back to the center and then draw your knees into the right shoulder. Keep repeating and as you do, keep the abs tight, keep your chin tucked in, elbows are not locked out, a little bit soft.

Now, if your need to make this move a little easier, it's probably because you need to build up some endurance and strength in your core area. But just hold this position, hold the plank. Shoulders are above your rib, elbows are soft, not locked out.

Just focus on tightening your abs, try to keep your lower back on sagging and breathe normally. Pull this, for as long as you comfortably can, working up to a longer period about thirty seconds to a minute. For an added challenge, walk yourself farther along, so that you are starting with your shins resting on top of the ball.

From here, tighten your abs, draw your knees into your left shoulder again, sliding that ball to the tops of your feet. Inhale as you come back, exhale as you contract and come in. If you feel unstable, just pause before you continue on with the movement.

Do 12-15 reps of each exercise and follow every move with a cardio burst for the best benefit. For more exercises, keep checking out prevention.com/fitness.