If you have access to a small, weighted medicine ball, try squeezing it behind your knee when doing rear leg lifts. It can intensify the exercise to help you get quicker results in less time. For added comfort and support, lean against a stability ball or simply perform the move on your hands and knees.
1 Kneel in front of a large stability ball on a level, padded surface. Grip a medicine ball between your right hamstring and calf muscles. Keep your heel pulled toward your buttocks to prevent the ball from falling out. Rest your upper torso against the ball, with your hands supporting you on the floor.