Winmax Yoga Ball Crafted from Professional Grade Stability ball leg curl: This move is basically a hip raise—but 1,000 times harder. To keep you stable and balanced, you abs should be pulling overtime while you are curling your hamstrings.By moving up and down,forward and backward,your body will get into better shape. Lie flat on your back with your lower legs placed on a stability ball Raise your hip and hold them that way.Curl the ball towards yourself,pause and uncurl it away.Lower your hip to starting position.That’s one rep. The stability ball is one of the most versatile pieces of fitness equipment, and is used by, physical and occupational therapists; It is also used as a replacement to the traditional office chair, as the simple act of sitting on the disc activates core abdominal and trunk muscles, strengthening and toning them throughout the day.