Squeezing an exercise ball between your feet for this back-strengthening move will help to tone the legs even more.
Lie on your belly, and hold an exercise ball between your feet. Engage your abs, and extend your arms straight out in front of you.
As you inhale, squeeze the ball and lift your knees, arms, and chest off the floor. Hold for a count of 10, and then slowly release your body back to the floor.