Nothing says health and vitality like a rockin' set of abs - and these moves will help get you there in as little as four weeks! Do the following workout two to three times per week, leaving 48 hours in between each session. Always pair it with a clean diet and frequent cardio for best results. 1. Extended Crunch on Ball, Part 1 Target Muscles: rectus abdominis, internal and external obliques Set Up: Position your upper back against a stability ball with your thighs parallel to the ground and feet flat on the floor. Extend both arms behind your head [A]. Action: Contract your abs and lift your back from the ball [B]. View next slide for move C. 2. Extended Crunch on Ball, Part 2 Bend your right elbow, bringing your arm to your side, then reach your left arm across your body [C]. Reverse, then repeat with your opposite arm. Do three sets of 10 reps on each side. 3. Russian Twist Target Muscles: internal and external obliques Set Up: Place your back against the top of a stability ball; your knees should be bent to 90 degrees and your feet flat on the floor. Hold a three- to six-pound medicine ball over your chest with extended arms [A]. Action: Rotate through your core to direct the ball towards the left; the ball should remain in the same position relative to your chest throughout each rep [B]. Slowly reverse to return to the start, then repeat on your opposite side to complete one rep. Do three sets of 10 to 12 reps in total. 4. Medicine Ball Woodchop Target Muscles: rectus abdominis, internal and external obliques, erector spinae Set Up: Stand with your feet wider than shoulder-width apart. Hold a three- to six-pound medicine ball with both hands and extend your arms up and to the left as shown [A]. Action: Contract your core as you twist through your waist to direct the ball to the outside of your right knee [B]. Reverse to return to the start. Aim for three sets of 12 reps on each side. 5. Bent-leg Side Plank Target Muscles: internal and external obliques, transverse abdominis Set Up: Begin by lying on your right side with your right knee bent to 90 degrees on the floor. (Your foot should be behind you.) Action: Place your right palm and forearm flat on the floor as shown, then lift your left leg from the ground. Hold this position for 30 seconds, rest, then repeat on the other side. Complete this move a total of three times on each side. 6. Side-lying obliques crunch Target Muscles: internal and external obliques Set Up: Lie on your right side with your legs stacked and your right arm extended beside your ear [A]. Action: Contract your abs and simultaneously lift your right arm and legs from the floor, supporting yourself with your left arm [B]. Hold for one count before lowering back to the start. Do three sets of 10 reps on each side. 7. Leg Lift and Lower Target Muscles: rectus abdominis, transverse abdominis Set Up: Lie faceup on a mat with your arms extended at your sides. Bend your knees and lift your legs so that your knees are over your hips and your calves are parallel to the floor. Action: Keeping contact between your lower back and the floor, slowly lower your feet towards the ground, maintaining the same 90-degree bend in your knees as you go. Make sure you stop before your toes touch the ground. Return to the start, and repeat for three sets of 15 reps.