Stand with your feet shoulder width apart with a flat back and your core braced. Keeping your chest up, bend at the knees and drive your hips back and down like you're sitting on a chair. You can simultaneously bring your arms up and out in front of you to provide a counter-balance. Lower slowly with control until your thighs are parallel to the floor, inhaling as you do so. Pause at the bottom, then lift your heels off the floor, squeezing your calves, lower them slowly to the ground then extend your legs and drive your hips forward to return to the start position, exhaling as you do so.