Place a stability ball between your back and a wall, and stand with your feet parallel and hip-width apart. Slowly squat to form a 45-degree angle with your knees (about half the distance of a regular squat), rolling the ball down the wall. Do not let knees extend over toes―they should be in line with your ankles―and keep abs pulled. Hold position for five seconds, then return to start, and repeat for 10 reps. (You can do this move without the ball, and just your back flush against the wall.
Tone your hips, thighs, and butt, plus build strong knee support.