Get the benefits of a health club at home

But if you're already at home, nobody's going to notice if you skip your 20 minutes on the treadmill, right? So try bringing the social aspect of the gym into your home routine. "Get a partner, or significant other to work out with you," says Geithner. Or log your minutes and miles together to keep you striving to stay on track.

And add variety to your workouts to keep you interested. "Get outside, and hike, jog, or ride a bike," says Geithner. "It keeps your routine fresh and it will throw you some more challenges." And while you're at it, make it a date. "I'm more likely to let myself down than I am someone else," Geithner says.

Another way to get the most out of your do-it-yourself fitness plan this year is to increase your non-exercise activity. Try to hit your goals each week, and then surpass them by being more active in your leisure time. And get the whole family in on the act. If you have a dog that needs to be walked, take the kids along, says Geithner, and make it long and brisk enough to raise your heart rates. Or play games like tennis or basketball with your family or friends. Even a robust game of catch can get the heart going.

The 2008 Physical Activities Guidelines for Americans recommends adults get at least two and a half hours of moderate aerobic activities each week, for at least ten minutes at a time. As a rule of thumb, these activities should allow you to talk comfortably, but should cause you to be too out-of-breath to sing. Some examples include, a leisurely bike ride, dancing, raking or trimming, doubles tennis, and walking briskly.

Or you can do more vigorous exercise for about half the time and still meet the government recommendation. In general, you can get the same benefit of 30 minutes of moderate exercise with 15 minutes of vigorous exercise. The rule of thumb for vigorous exercise is that you'd struggle to say more than a few words at a time without stopping to catch your breath. Some examples include, basketball, jumping rope, martial arts, race-walking, jogging, running, fast or uphill bike-riding, soccer, swimming, and singles tennis.

You should also aim for strengthening exercises, such as push-ups, sit-ups, or weight lifting, at least two nonconsecutive days a week. For more on the 2008 Physical Activities Guidelines for Americans, see the Be Active Your Way guide for adults, which includes forms to track your progress.

—Kevin McCarthy, associate editor

For more information and workout tips, see our New Year Fitness guide, which includes our coverage and Ratings of exercise equipment and infomercial exercise machines, and the secrets of skinny people.