Lay on your back with your knees bent. Bring your knees up over your hips and place your palms on your thighs above your knees. Keep your elbows straight. Begin pushing your hands into your legs and pulling your legs into your hands; do not move**. Tighten your abdominals to produce the force you are putting into the push from your hands and legs. The more intensely you press the harder it will be. Start with about 50% of max effort and adjust accordingly form there. Try this for 10-30 seconds.
Muscles Targeted: (1) abdominals (2) hip flexors