From the crunch to the bicycle twist, there are a number of exercises to challenge your abdominal muscles. If you are looking for a more advanced abdominal exercise, the jackknife crunch is ideal. This challenging exercise requires a sharp, explosive movement to build your stomach muscles using only your body weight and a weight bench if you desire. Always check with your physician before beginning any exercise routine to ensure your body can perform the exercise.
The jackknife exercise involves lifting your body up from an extended position and pulling your knees in toward your chest. Lie down on your back with your hands above your head and your legs extended. In one fluid motion, lift your hands toward your legs and lift your legs toward your chest. You can either bend your legs in toward your chest or you can leave your legs extended. Focus on working your abdominal muscles instead of using your hips to lift your legs toward your chest. Keep your back straight as you lower your back and legs toward the ground, stopping just short of putting your shoulders and feet on the ground. Repeat the exercise 10 to 15 times.
Finding the right angle to extend your legs can be difficult. The lower your legs are to the ground, the harder your abdominal muscles will work. As you advance in the exercise, try to hold your legs about 35 to 45 degrees away from the floor. Carefully breathing in and out is important because it can aid in how you contract your stomach muscles. Take a deep breath in, then exhale to lean your shoulders back and work the stomach muscles, according to Weight Watchers. Inhale as you return to your starting position.
The jackknife crunch exercise chiefly targets the rectus abdominis muscles, which are the muscles that cross the middle of your stomach. These are often simply referred to as the вЂњabвЂќ muscles because they are responsible for building the "six-pack" definition in your stomach. Other muscles that support and work with the jackknife crunch include the obliques on the sides of your abdominals, your inner thigh muscles and your hip flexors that bring your knees toward your chest. Note that the exercise requires an intense contraction to work properly. You must flex the waist -- bringing your stomach as close to your knees as possible -- for the ab and oblique muscles to strengthen, according to ExRx, an anatomy and physical therapy website.
Although the jackknife crunch can be performed on the floor, you can up the intensity by using a weight bench. By using the bench, your legs can potentially dip lower, meaning your abdominal muscles must resist against gravity more. Scoot your buttocks to the edge of your weight bench and grasp the end of the weight bench with your hands. Inhale, then exhale as you contract your stomach muscles and bring your chest toward the top of your legs.