Stand with your feet hip width apart, your toes slightly turned out and a short band just above your knees. 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. Make a soft landing by bending your knees as your feet touch down. Repeat the sequence for the required number of reps (or time).