Stand with an aerobic step (or weight place) roughly one foot in front of you, with a barbell on your back. Stand tall with your core braced and a flat back. Take a big step forward onto the aerobic step with your left leg. This is your start position. Proceed to bend at the knees, 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 to returning to the start position. Repeat for the required reps (or time) and then change legs.