Whether you're trying to find a way to maximize the effects of your waist-trimmer belt through fat burning core exercises, or you're simply trying to add a new twist to your workout routine, it's fair to say that sit-ups can be a fairly boring, and monotonous form of exercise. Fortunately, if you're having trouble staying motivated in your old regimen, then it may help to know that there are numerous sit-up variations out there that you can use to build flexibility and strength, while cutting down on unwanted stomach fat.

While endless sit-ups in your waist-trimmer belt might not immediately deliver the six-pack you've always wanted, they're definitely a crucial part of the puzzle, and by switching up your workout with new variations, you can make sure that your ab routine doesn't send you to sleep.

1.    Standard Sit-up

Before we get started looking at some of the more exotic sit-up variations, it's important to make sure you know how to maximize your form with the standard exercise. Lie on your back with your knees bent, and pointing upwards. Put your hands behind your head - but make sure that you don't use them to pull your neck away from the floor during each rep. As you exhale, contract your abs, lifting your shoulder blades and head away from the ground, then inhale as you lower back down.

2.    Reverse Sit-up

Some sit-up variations are designed to focus on different parts of your abdomen. This option targets the lower abs, which is ideal for people looking to eliminate extra inches around their gut. Start by lying on your back with your knees bent at about a ninety-degree angle with your hips. Line your shins up parallel to the floor, and situate your arms next to your body, palms facing the floor. Exhale as you contract the lower abdominal muscles and lift your backside away from the ground. Inhale as you release and fall gently back into the starting position.

3.    Raised Leg Sit-up

For these sit-up variations, combine the stability work of a reverse sit-up with the challenge to your core that a standard crunch offers. Lying on your back in the same position as a reverse crunch, stay grounded and bring your hands behind your head. As you exhale, crunch upwards, and as you inhale, lower your body back down. Lift one leg at a time away from the floor during each sit-up.

4.    Weighted Sit-up

Once you've mastered the standard and reverse crunch options, try adding some weight to the movement to challenge your core. Start in the same position as with any standard crunch, and hold a ten-pound medicine ball against your chest. As your strength improves, you'll be able to try weighted sit-up variations with a heavier ball, or set of dumbbells.

5.    Frog Crunch

Finally, when it comes to sit-up variations, the frog crunch not only challenges your stability and balance, but also strengthens your core and targets unwanted fat around your lower abs. Start in a sitting position with your knees bent outwards in front of you. Lean backwards so that you're holding your torso at a 45-degree angle to the floor, and your shins are parallel. Keeping your abs engaged, straighten your legs and bring your arms out to the side.