Regular: in standing position, step one leg forward to a lunge and bring both arms over head in swinging motion. When performing a lunge, be careful to not let the knee come over your toes. If your knee comes over the toe too much, try taking a larger step forward, or try the modification until you are comfortable doing forward lunges.
Modification- if regular lunges bother your knees, try this variation: instead of stepping forward, step backward, in a reverse lunge.
For either the regular or modified lunge, it is important to maintain form. Your legs should move, your body should not. Your body should resemble a carousel horse with a pole through its body, going up and down only because the legs are moving in that motion.
Count either one leg or one full cycle as a repetition.