1. Boost your brain power. Exercising your body can help build your brain too. A study at the University of Illinois at Urbana-Champaign put a group of sedentary 60- to 79-year-olds on an exercise program three days a week, having them walk for up to one hour. After six months, the exercisers' brain volume had increased and they experienced a 15 to 20 percent improvement in memory and other brain functions.

2. Build muscle strength for life. It's true that if you don't use it, you will lose it -- especially when it comes to your muscles. Muscles have a tendency to atrophy with age, causing older people to have difficulty doing simple things such as getting out of a chair, climbing stairs or getting up after a fall. But there's a simple way to ensure that doesn't happen. Lift weights (heavy ones will give you the most bang for your buck) a few times a week. Start now, and don't ever stop!

3. Whittle your waistline. Controlling your weight is important, but where you carry that excess weight matters just as much. Harboring fat around your middle has been shown to increase your risk of heart attack, diabetes , some cancers and even dementia.

4. Lower your stress level. There's a reason why you feel more relaxed after a tough session at the gym or a brisk walk around the neighborhood -- exercise can relieve stress, release tension and generally improve your outlook on life.

5. Reduce breast cancer risk. Numerous studies have linked increased exercise with decreased risk of breast cancer. The prevailing theory is that physical activity helps lower levels of estrogen and other hormones that can fuel the growth of breast cancer tumors. A recent study published in the Journal of the National Cancer Institute reported that women who were physically active in their teens and 20s reduced their risk of being diagnosed with premenopausal breast cancer by 23 percent. And the benefits don't stop once you hit middle age -- continuing to exercise regularly (at least three hours of strenuous exercise a week is ideal) will continue to help reduce your risk of the disease.

6. Sleep better. While vigorous exercise right before bed may leave you too revved up to fall asleep immediately, studies have shown that regular exercise earlier in the day can help people fall asleep more easily and sleep more soundly.

7. Strengthen your bones. High-impact exercise in your teens, 20s and 30s is important for building up bone density. But even later in life, continuing to do both weight-bearing activities (like running, playing tennis or jumping rope) and resistance exercise (like lifting weights) can help you maintain the bone mass you have.

8. Stave off heart disease. The heart is a muscle, and -- like all your other muscles -- it enjoys a good workout. But exercise does more than just strengthen your heart. It also helps lower blood pressure, increase HDL (good cholesterol) levels and reduce LDL (the bad kind), all of which are important factors in reducing your risk of heart disease.

9. Lift depression. Endorphins (the so-called "feel good" hormones) are released during exercise. At the extreme, they can lead to the sort of exercise-induced euphoria commonly known as the "runner's high." But even small doses of exercise -- and the resulting hormones -- have the power to improve your mood.

10. Prevent diabetes. Several million Americans suffer from Type 2 diabetes. And yet, according to the American Diabetes Association, just 30 minutes of moderate activity every day, combined with a 5 to 10 percent reduction in your weight, can mean a 58 percent reduction in your risk of diabetes.