The core muscles are among the most important in your body. They're the center of your body, supporting your back and keeping you standing straight. Most people can measure the strength of their bodies by measuring the strength of their stomachs. If the abs are fit, the rest of the body will be, too.

If you're one of the 80 percent of Americans who suffer from back pain because of weak abs, these moves will help. Better yet? There are no traditional crunches among these ab-strengthening moves.

1. Lower Tummy Toner



Lie on your back with your legs bent in the air at a 90-degree angle and put a rolled-up hand towel between your knees. Place your arms by your sides with your palms on the floor. Lift your hips off the ground. Pull your belly button in and press your inner thighs together. Use your abs -- not momentum -- to lift your hips. Complete as many as you can in one minute.

2. Double Crunch



Lie on your back with your legs bent at a 90-degree angle in the air with a rolled-up towel between your knees. Bend your elbows and place your hands behind your head. Bring your lower and upper body in toward each other and crunch. Be sure you're pulling in your abs. Complete as many as you can in one minute.

3. Knee Twists



Lie on your back with your legs bent at a 90-degree angle in the air with a rolled-up towel between your knees. Extend your arms out to the sides on the floor. Keeping your legs together, lower your knees to the left side. Keep your upper body still and your abs engaged. Switch sides, bringing your knees to the right. Alternate sides repeatedly. Complete as many as possible in one minute.

4. Flutters



Lie on your back with your legs extended straight up toward the ceiling. Place your arms by your sides, with your hands underneath your buttocks -- this will really work your lower abs. Point your toes. Lift your head and shoulders off the floor and alternate crossing your legs in front and back of each other, progressing to a 45-degree angle. Then, slowly crisscross back to the starting position. Complete as many as you can in one minute.

5. Plank Pull-Ins



Position your body in a plank. Keep your abs pulled in, back straight and head extended so that your body forms one long line from the top of your head to your heels. Bend your right leg, bringing the knee toward your chest. Straighten the leg and bring your left knee toward the chest. Continue alternating for one minute.

Denise Austin has helped millions of people lose weight. She's sold 20 million exercise DVDs, authored more than 10 books and starred in the most-watched fitness show in history! Austin's mission is to help America get fit –- and now she's online at DeniseAustin.com to motivate and educate people everywhere to eat right and exercise. Visit DeniseAustin.com to lose weight!