Seven top trainers share their secrets to flatter abs and a slimmer waist.

By Mallory Creveling

The case for sculpting a strong core is pretty airtight: It helps promote ballerina-like posture, ensures a healthy back and makes you steadier on your feet. Not to mention, a toned waist looks pretty good. While eating right and getting in extra cardio are critical if you want to reduce fat, so are these shape-shifting moves. So skip the sit-ups and hit the mat for exercises that work your middle from every angle.

1. Your Motivator: Sadie Kurzban, founder and CEO of 305 Fitness, a dance-based workout

The Move: Plank with Knee Taps

Get into low plank position, elbows in line with shoulders and resting on forearms. Squeeze your entire body so that core, glutes and back muscles are engaged. Keeping toes on the floor, tap knees, one at a time, on the ground. Your body should stay in a straight line—don't let hips rise or drop. Continue to alternate for one minute.

Pro Tip: To move faster and up the burn (along with the fun factor!), turn on a jam with a quick beat and tap to it. Sadie loves Jennifer Lopez's "Ain't Your Mama."

2. Your Motivator: Amy Opielowski, instructor and senior manager of quality and innovation at CorePower Yoga

The Move: Bicycle Crunches

Lie flat on your back with fingertips placed lightly behind ears and elbows wide. Lift both feet off the floor until knees stack above hips at a 90-degree angle and shins are parallel to the floor. Raise both shoulder blades off the ground, moving your left shoulder toward your right knee and extending left leg. Hold for two seconds. Switch to the other side, moving right shoulder toward left knee and extending right leg. Continue alternating. Complete 15 reps on each side.

Pro Tip: You may already be familiar with this exercise, but it's one of the best for working the entire midsection and whittling your waist. Remember to focus on your breath, inhaling and exhaling as you turn side to side.

3. Your Motivator: Rob Piela, owner and creator of Gotham Gym and Gotham G-BOX

The Move: Woodchopper

Stand tall with feet shoulder width apart and knees slightly bent. Hold a medicine ball or dumbbell with both hands. Bring the weight up to your right shoulder. Exhale, bringing the weight across your body and toward the left knee as you turn your upper body toward the left. Repeat with the other side and continue alternating. Complete 15 reps on both sides.

Pro Tip: Engage your abs and twist your entire torso—not just your arms—so you work your obliques.

4. Your Motivator: Jenn Seracuse, director of Pilates at Flex Studios in NYC

The Move: Seated Reverse Crunch

Start seated at the edge of a mat with knees bent and heels on a folded towel placed in front of it. Make sure you're working on a hard surface so the towel can slide back and forth easily. Extend arms straight out in front of your body. Round your lower back and tuck pelvis upward, engaging abs. Maintain this position as you extend the legs forward, sliding the towel. Then bend the knees to bring it back toward the mat as you focus on your ab muscles. Repeat for one minute.

Pro Tip: Think about lifting the knees, rather than pulling them toward the chest so you work your abdominals more than your hip flexors.

5. Your Motivator: Suzanne Bowen, creator of the BarreAmped DVD series

The Move: Neutral Leg Lowers

Lie on your back with spine in a neutral position. (You should feel the curve of your lower back lifting slightly off the mat.) Place arms down beside hips. Bring legs straight up above hips. (It's okay if knees bend slightly.) Exhale and lower legs a few inches, maintaining the natural curve of the spine. Inhale and lift legs back up. Repeat 10 times.

Pro Tip: Modify this move by bending arms and pressing forearms into the mat beside the rib cage. Or up the challenge by lowering legs nearly to the ground.

6. Your Motivator: Toby Massenburg, group fitness manager and creator of the Best Abs Ever class at Equinox

The Move: Starfish Toe Touch

Lie on your back with arms and legs extended. Separate arms slightly wider than shoulders and legs slighter wider than hips. Crunch up, lifting shoulders off the ground as you raise legs 45 degrees off the floor. (This is your starting position.) Put right hand behind your head. Lift right leg as you reach your extended left arm toward it. Return to starting position. Repeat on the other side, lifting left leg and moving right arm toward toes. Return to starting position. Continue alternating, doing 10 reps on each side. Keep knees straight the entire time with shoulders and legs lifted.

Pro Tip: This works the deep core muscles that stabilize your spine. If you need to take it down a notch, hold legs slightly higher, but try to keep them below a full 90 degrees.

7. Your Motivator: Brian Zehetner, director of health and fitness at Planet Fitness

The Move: Modified Spiderman Plank

Start in a traditional high plank with elbows straight. Bend left knee, bringing it forward and across your body to the right elbow. Keep shoulders over wrists and pelvis in a neutral position. Return to start. Repeat with right knee. Continue alternating for one minute.

Pro Tip: Practice this exercise in front of a mirror to make sure you're in a straight line from shoulders to ankles. If you need to start off easier, try bringing your right knee to your right elbow and left knee to left elbow instead.