HOW: Get a swiss ball ideally set-up between a wall and your back, have it initially placed in your low back region near waist height. While keeping pressure into the ball and the ball, lift one leg up, keep your balance, perform a squat and repeat.
FEEL: You will feel your leg muscles, especially quads and glutes working with this exercise.
COMPENSATION: Do not lose ideal squat form technique, do not let your knees collapse in or bow out, do not lose pressure into the ball into the wall. Do not let your hip drop on the side you have the leg lifted.