The supine alternate lower extremity march is designed to strengthen and improve the recruitment of your lower abdominal muscles, which provide support for your low back.
Begin lying on a mat with your knees bent and feet flat on the floor. You may place your fingers on your lower abdominal muscles just inside your hip bones so you can feel when they are contracting.
Tighten your lower abdominal muscles and lift one knee up toward the ceiling like you are marching. Lower your foot back to the starting position. Relax. Repeat on the other side.