For a great all-around exercise, it's hard to beat the crossover reverse lunge. It will strengthen your lower back, abs, thighs and hamstrings. The crossover reverse lunge has many variations that will ensure that your back is in top condition.
Stand with your feet shoulder width apart, and then step backward to the reverse lunge position. Remember to keep both knees at a 90 degree angle -- do not overextend. As you're performing the reverse lunge, rotate your torso across the front leg. You should feel the tension in your lower back, thighs and abs. Hold this position for a couple of seconds before returning to the starting position. Repeat the movements with the other side of the body, making sure to bend across the opposite leg [source: Body Building].
Once you've become comfortable with the exercise and feel ready for a new challenge, try hugging a weight to your chest as you lunge and turn. This variety of the crossover reverse lunge will strengthen your arms as well.