There’s no question crunches can do a great deal to flatten your core, but they are not the most effective workout when it comes to a flat belly.
A number of fitness instructors recommend planks or exercises using a medicinal ball rather than crunches simply because these target your entire core.
Side Plank Crunches
This is a more interesting plank variation as it also targets your obliques. Start in a side-plank position – one foot on top of the other, your abs and butt tight. Bend your top arm then bring your top knee toward your top arm in a side crunch. Go back to the starting position and repeat 10 times before switching sides. Do 3 sets of 10 reps per each side.
Medicine Ball Twists
This Russian twist variation using a medicine ball will do wonders for your core. Lie on your back, your knees bent, your feet on the floor. Hold a medicine ball to your chest. Lift your torso to a 45-degree angle from the floor. Bring the medicine ball to one side, touching the floor if you can. Do the same on the other side. Increase your speed while doing the exercise. Do 2-3 sets of 20-30 reps per side.
Medicine Ball Jackknives
Medicine ball jackknives are some of the most effective exercises for working your core in very short time. Lie down, your legs straight. Hold a medicine ball above your head. Raise your legs up keeping them as straight as possible while bringing the medicine ball toward them. Lower down slowly then repeat. If you find them difficult at first, bend your knees toward your chest instead of keeping your legs straight. 3 sets of 10-15 repetitions per side will make your abs burn.
Mountain Climber Crosses
This workout is a variation of the classic mountain climber exercise. It targets the entire core including your shoulder muscles. Get into a plank position, your shoulders right above your hands. Tighten your core then bring one knee across your chest toward your opposite hand. Go back to the starting position then do the same with your other knee. Increase your speed as much as you can while keeping your core tight. Do 3 sets of 50 reps.
Split Leg V-Ups
This is just another effective ab exercise that’s strongly recommended by fitness experts. Split leg V-ups does wonders on your abs and is far better than crunches. Start by lying on your back with your arms straight above your head. Pull your belly button toward the floor then raise your right leg bringing your foot as close to your arms as you can. Go back to starting position. Repeat on the other side. Do 3 sets of 10 reps per side.