Place a lightweight medicine ball between your knees and lie flat on your back, arms at your sides, abs engaged, lower back flat on the floor, and legs lifted into a table-top position (knees bent, knees in line with hips and shins parallel to the floor).
EXHALE: Keeping abs engaged, knees bent and upper body relaxed, use your abs to pull your knees toward your chest. INHALE: Slowly return your legs to the starting (table-top) position to complete one rep.
You may want to place your hands underneath your lower back for support. Don't use momentum to swing your legs in; practice control.
Muscles Worked: Abs, Inner thighs