Stand with your feet hip width apart and your toes slightly turned out. Bracing your core and keeping your chest up, bend at the knees and drive your hips back and down as if you are going to sit on a chair. Lower until your thighs are parallel to the floor or deeper depending on your range, making sure your knees are pointing in the same direction as your feet and that your lower back doesn't collapse. Inhale throughout this lowering phase. Once at the bottom, in one explosive movement, push through your feet extending your knees and hips and jump up as high as you can. Sharply exhale as you do so. As you make a soft landing by bending your knees as your feet touch down, bring you feet together so you land in a narrow squat. Repeat the jumping motion, this time jumping your feet apart so you land in a wide squat position. Repeat this sequence for the required number of reps (or time).