Lay on a mat with your butt under the bar of the smith machine. Place your feet at close-stance on the bar. Use your feet to unlock and inhale as you lower the bar down, your knees will come down to the sides of your body or chest, depending on your flexibility. Exhale as you press through the heels as you push the bar up. Repeat this sequence for all reps and use your feet to re-lock the bar.