Stand with your feet shoulder width apart with a flat back and your core braced. Place your hands on either side of your head with your elbows parallel to your torso. Keeping your chest up, bend at the knees and drive your hips back and down like you're sitting on a chair. Lower slowly with control until your thighs are parallel to the floor, inhaling as you do so. Pause at the bottom, then extend your legs and drive your hips forward to return to the start position, exhaling as you do so.