Stand tall with a barbell resting across your upper traps and not on your neck. Grip the bar with your hands comfortably wider than shoulder width. Brace your core and keep your chest up. This is your start position. Take a big step backward with your left leg and bend at the knee, slowly lowering your body until your front knee is bent at least 90 degrees, whilst your rear knee should be hovering just off the floor. Inhale as you do so. Keep your torso upright the entire time and look forward. Pause at the bottom of the movement, then extend your knee as you push off from your left foot to move forward and return to the start position. Repeat on the other leg. Continue to alternate legs until all the required reps (or time) are completed.