This exercise is an effective one for developing leg strength and also works the upper-body stabilizing muscles. It requires a reasonable amount of strength and stability.
STEP 1. Stand with your feet hip-distance apart and with them facing forward and rest the bar on the back of your shoulders just above your shoulderblades. Pull your abdominal muscles in before starting the movement, but not so tightly that your breathing patterns are affected.
STEP 2. Inhale slowly and start the movement at your hips by pushing them out behind you in a sitting motion. Then allow your knees to bend, making sure that they do not travel forward over your toes.
STEP 3. Travel down until your knees are flexed at 90 degrees at a comfortable point, exhale slowly and push your body weight up through your heels to straighten your legs.