Tip: Print out this form so you can follow along as you watch the video. The instructions on this form can be a helpful resource while practicing this exercise.
When the bent knee lift gets too easy, it's time to move on to the supported heel glide exercise. It's called "supported" because you'll keep one foot flat on the ground, supporting your low back.
Doing the supported heel glide requires a bit more core strength and control than the bent knee lift exercise.
Lie on your back with your knees bent and your feet on the ground. Bring one knee up until it points to the ceiling. Engage your core, and slide the opposite foot along the floor until the leg is straight. Then slide the foot back to the starting position in which the knee is bent. Repeat for the opposite side.
Be sure to keep your back in its neutral position at all times during the exercise. If your back begins to arch as you slide your leg downward, only slide your foot part way down. Move slowly to allow gravity to have its greatest effect.
Avoid arching your back during the exercise, as this means you are compensating with other muscles. Move slowly as you exercise so that gravity can provide a challenge to your core muscles.