Physio Ball Knee Tucks This exercise works to stabilize your lower back, abdominals, obliques and muscular balance. You begin this exercise by being on your hands and knees near the physio ball, then carefully place your feet up on the ball and straighten your body so you are in a declined push up position. Begin the movement by using your lower abdominals to tucks your knees in towards your chest and roll the ball along the top side of your ankle, foot and legs. If needed you can rest the ball more towards your needs to give make the motion a bit easier and give you more room to perform the knee tuck. Complete 15-20 repetitions of this exercise and three total sets.