If you want to be happier ? move your body. In fact, PE class should have been called Happiness 101! For my new book, Happy for No Reason: 7 Steps to Being Happier from the Inside Out, I interviewed scores of experts, as well one hundred unconditionally happy people, and research overwhelmingly shows that people who exercise are happier. You can transform your life by making some form of exercise or movement, such as walking, running, swimming, dancing, Qigong or yoga, a regular habit.

When you exercise, your brain gets more oxygen, but even more importantly, it causes your body to produce valuable chemicals and hormones that impact energy, mood and health. In a recent study done on athletes, Harvard psychiatrist John Ratey found that dopamine, serotonin, norepinephrine ? those wonderful happiness chemicals ? were all elevated after exercise. In fact, dozens of studies indicate that exercise is often as effective for reducing depression as the typical medications prescribed.

Exercise can also help relieve and prevent anxiety, creating a calming effect that lasts for about four hours after exercising. Try getting in a fight right after a rigorous workout. It's not likely to happen! Exercise also increases endorphins, the "bliss" neuro-chemicals responsible for that wonderful "exercise high," by about 500 percent.

Dr. Henry S. Lodge, assistant clinical professor of medicine at Columbia University and co-author of Younger Next Year, explains how exercise works at the cellular level to keep you vital and healthy. He says that every day you replace about 1% of your cells, getting a whole new body every three months. When you exercise, your muscles release specific substances that tell your cells to grow. When you sit around like a couch potato, your muscles let out a steady trickle of chemicals that tell your cells to die. What powerful motivation! If you started exercising in January, you could have a whole new body of strong, happy cells by April.

You can even energize your body and boost your happiness without leaving your chair. Brian Siddhartha Ingle, an osteopath specializing in a neuromuscular education program called Hanna Somatics, told me that he sees daily how people's posture affects their energy and level of happiness. Next time you're feeling stressed, anxious, or blue, notice if your shoulders are coming up toward your ears. Instead of trying to pull your shoulders down, Dr. Ingle suggests exaggerating this movement by bringing your shoulders even closer toward your ears ? then, SLOWLY, letting them come down. Do this 3 ? 4 times and see if your stress and anxiety levels go down.

Our bodies can help or hinder our ability to experience happiness, so this year, make a commitment to pay attention to your physical well-being. You don't have to join a gym, run a marathon, or pump iron ? unless you want to ? to become happier. Simply finding a way to move your body on a regular basis will work wonders and keep your smile in good shape, too.

(Excerpted from the New York Times bestseller, Happy from No Reason: 7 Steps to Being Happy from the Inside Out, Free Press, January 2008, and reprinted with permission of the author, Marci Shimoff).