Beyond firming your belly, strength in the abdominals is essential because the abs' central location in the torso makes them a linchpin of bodily movement.

The abdominal muscles consist of four muscle groups layered at the front and sides of the torso. They are crucial for keeping your trunk firm, allowing you to bend and twist at the waist while providing the leverage you need to exert force with other parts of the body. They also support the spine, so strengthening them reinforces the back and protects you against lower back pain. Strong abs also promote a good, erect posture.

The abdominals are among the few muscles in the body that can stand up to being worked every day, and can also stand up to high numbers of repetitions.

To get rid of midriff flab, you'll need a healthy diet, fat burning aerobic exercise, and whole body muscular fitness. But to get that toned, firm stomach or washboard look, crunches are the best abdominal exercises to do.

Basic Crunches:

1. Lie on your back with elbows out to the sides, hands at your temples or cupped behind your ears (not grabbing the back of the neck), or cross arms over your chest. Your head should be a few centimeters off the mat, chin tucked slightly forwards. Feet should be flat on the floor, next to each other about 5 inches (15cm) from your buttocks, with knees bent at 45 degrees. Keep the legs slightly apart.

2. Pushing the small of your back into the floor, slowly curl your upper torso up towards your knees, raising your shoulder blades (but not your lower back) off the ground. Hold for a second. Lower to the starting position, but do not relax between repetitions.

Don't hold your breath. Exhale as you crunch forwards, inhale as you lower yourself to the starting position.

1. Assume the same starting position as for the basic crunches. If you cross your arms over your chest on crunches, make sure you have your hands at your temple or cupped behind your ears for these, elbows to the side of your head. Raise shoulders off the floor, curling your torso up towards your knee.

2. Twist your trunk slightly so that your left elbow points towards your right knee. Hold for a second, return to the starting position without relaxing your abdominal muscles, then repeat, raising your right elbow towards your left knee. Continue alternating.

Oblique Crunches:

These provide an extra dose of exertion to the obliques.

1. Lie flat on your back, hands at your temples or cupped behind your ears. Let your legs fall to the right side, so that your upper body remains flat on the floor while your lower body lies on its side.

2. Keeping the shoulders as parallel to the floor as possible, lift your shoulder blades off the floor. Do not aim an elbow at one knee. Hold for a second, and then lower to the starting position. Do 10 to 20, then drop knees to the opposite side and repeat.

Raised Leg Crunches:

Lie flat on your back with your knees bent and lower legs supported by a bench or chair. Your thighs should be at 90 degrees to the mat. Tilt the head forward to 45 degrees and hold your hands at your temples or cupped behind the ears. This is the starting position. Slowly crunch forward, breathing out as you do so, then slowly move back to the starting position while breathing in. Repeat, but don't relax between reps.

Never pull on your neck during a crunch. Doing so may injure your neck or upper back.

Bench Crunches:

These work upper, lower and oblique abs.

2. Bring your upper body to an upright position while pulling your knees into your chest. Hold for a second, and then return both the upper and the lower body to the starting position.