As I wrote in the article about classic crunches, the main task of the rectus abdominal (which forms those desired six-pack) – to pull ribs to pelvis (like in front crunches) or pelvis to ribs (like in reverse crunches). Though for the muscle itself there’s no such a difference, it is considered, that front crunches work better on the upper section, and reverse ones – the lower.
Performing the exercise: lay on the floor, completely bent your legs in knees and hips. Straighten your hands by your body, palms down (photo 1). Using abdominals get your pelvis off the floor and hold this position for few seconds (photo 2). Slowly go back to the starting position and repeat required number of reps.
Notice: do not try to move your legs maximum back/behind, your task – is to close the pelvis to the ribs (to continue the movement, other muscles will switch on, which gets the load off the abdominals). Lean on the floor with your palms – this will help at the starting point. To regulate the load on abdominals try to gradually straighten your legs, so that in lower position they were perpendicular to the floor (feet up): this is the hardest variation.
If your hand force is not enough – try another variation of regular crunches: straighten your hands above the head and grab the stable pillar (bed or closet). Bend your knees completely, and your hips to the right angle with core. Perform crunches by lifting your pelvis, the angle between hips and stomach should stay constant. Upper back should stay on the floor. When you have felt the maximum abdominals tension, hold on for few seconds and slowly go back to the starting position. Other crunch rules stay the same: keep full movement control (especially in going down phase), exhale – rise up, inhale – go down, put something soft under your lower back, hands are not necessarily straight, you may bend them a little.
As I said at the beginning, crunches – is the most famous, but not the best exercise for abs. If you are aiming on strengthening your abdominals, I advise you to also include different leg rises and static holds (“L-seat”). But don’t forget – the way to desired six-pack lays not only through abs training, but through getting rid of excessive fat, which (especially men) is accumulated in waist section. For this you should reconsider you ration and include energy consuming, multi-joint exercises to your training program (for example squats, push-ups or at least plank)
Good books to read:
Bret Contreras. Bodyweight Strength Training Anatomy – Human Kinetics, 2013 – 224 p.
Kavadlo Al. Pushing the Limits: Total Body Strenght with No Equipment – Dragon Door Publications, 2013 – 224 p.
BJ Gaddour. Your Body Is Your Barbell: No Gym. Just Gravity. Build a Leaner, Stronger, More Muscular You in 28 Days – Rodale, 2014 – 288 p.