By now, you should be seeing significant benefits from your aerobic workouts, and we don't just mean on the scale. You should be able to do more physically, whether that's climbing a few flights of stairs without getting winded or running further in a shorter period of time. But to reap even more benefits, you should consider adding strength training to your routine if you haven't already done so. One of the major perks of strength training is that it builds and maintains muscle; the more muscle you have, the more calories you'll burn. To learn more about strength training and how to get started, check out The Secrets to Strength Training.

And for a complete strength-training routine you can do in just 20 minutes, check out Bob Greene's Basic Eight.