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Step 1
Get in position. Start by lying on the floor with your knees propped up at a 45-degree angle. Post your right foot onto your left leg. Place your hands behind your head or make fists and place them next to your ears. Make sure to tense your abs so that your lower back is nearly flush with the ground.
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Step 2
Raise up and twist. For the first part of exercise, raise up like you would with a regular crunch. Keeping your neck straight, contract your ab muscles and lift your face to the ceiling. As you near the top of the contraction, twist from your left elbow to your right knee. Squeeze at the top and try to touch your elbow to your knee in a controlled motion.
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Step 3
Lower back down. To lower down, reverse the upward motion but keep your abs tensed. You should maintain enough control on the down phase to prevent yourself from falling back. Lower yourself until your lower back touches the ground and then lift back up for the next rep. After your first set, change to your left foot propped up and your right elbow lifting to touch your left knee.
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Step 4
Vary the exercise. Once you've mastered the basic form of the knees to elbow ab exercise, you should do a more intense variation. Instead of propping up your knee, put your knees in the air, bent at a 90-degree angle. Begin by lifting your left elbow as you raise your right knee to meet your elbow. Reverse the motion and then do the next rep with your right elbow to your left knee.
