Place a lightweight medicine ball between your ankles and lie flat on your back, arms at your sides, abs engaged, lower back flat on the floor, and legs extended straight up in line with the hips.
INHALE: While maintaining a perfectly flat back, hinge from the hips to slowly lower your straight legs toward the floor while squeezing the medicine ball tightly. EXHALE: Use the abs to slowly lift your legs back up to the starting position to complete one rep.
This exercise should be mastered without a medicine ball first. Only lower your legs toward the floor as far as you can while maintaining a neutral or flat lower back. If your back arches from the floor, you have lowered too far and are increasing your risk of injury. For greater support and comfort, you can place your hands underneath the lower back instead of at the sides.
Make it easier: Instead of keeping your legs straight, bend at the knees to decrease the challenge.
Muscles Worked: Abs