Stand tall with a neutral spine and your feet hip width apart. Hold a barbell in your hands with an overhand grip and hands slightly wider than hip width apart. Raise the barbell upto your shoulders, so it's resting just below your chin with your palms pointing up. This is your start position. Bend the knees, hips and ankles to dip slightly. Use your legs to explosively drive your the barbell up and directly over your head, extending your arms and exhaling as you do so. Slowly return to the start position inhaling as you do so. Repeat for the required number of reps (or time).