Body Banao

Sit-ups are the most common exercise to train the abs, though they are quite useless. In severe cases they can cause injury. They can shorten hip flexors, drooping shoulders and cause back pain. The better option is the Reverse Crunch.

The Reverse Crunch is the antagonistic movement of the Sit-up. While it has no problems associated with a Sit-up, it can improve your posture.
Makes Your Abs stronger. Particularly your external obliques.
Check Lordosis. The exercise teaches you to lean your pelvis backward and fortifies your abs. This rectifies lordosis.
Avert Kyphosis. As there is no depression of your ribcage as when you do sit-ups, the upper-back doesn’t round (kyphosis).

Reverse Crunch Method.  Recline back on the floor. Bend your knees. Bring your knees to your head by crunching your abs. Return to the start. A dumbbell or medicine ball can be used as counter weight.
Lean Your Pelvis Backward. Press your lower back into the floor on every rep. There should be no space between your back and the floor.
Your Feet should be Down. Prevent them from being lifted during the motion. Your knees should be bent, near your glutes.
Your Head should be Down. Knees go closer to your head, and not vice versa. So your head should always be on the floor.
Exercise Your Abs. Keep your hip flexors out of the picture. Your legs should not move beyond 90 degrees, while lowering.

General Mistakes. Strength deficiency can make your body use wrong movement pattern while performing Reverse Crunches. Here are few of the common mistakes:
Curving Your Lower Back. Harmful for your spine. Bend your pelvis backward when every rep commences. Press your lower back into the floor.
Stretching Your Knees. Simplifies the exercise. Keep an object between your legs, to prevent cheating.
Excess lowering. Includes your hip flexors. Prevent your thighs from going below perpendicular while lowering.
Lifting Your Head up. Leads to forward head posture, which is cheating. Your head should touch the floor.

Reverse Crunch Advances.  To develop more muscular abs, they must become more muscular. Hence the Reverse Crunch should be taxing.
Reduce The Weight. Grab a 45lbs/20kg dumbbell or heavy medicine ball. Reduce he weight as your abs become stronger.
Eliminate The Weight. Don’t use counter weight. Place your hands at the back of your head and crunch your abs.
Change over to Dragon Flags. With your hips & knees straight, crunch your abs.

This exercise can be done at the end of each workout since it is add-on. Concentrate on squat and deadlift to build muscle and then shed flab to get the 6 pack.