According to the U.S. Surgeon General's 1996 Report on Physical Activity and Health, more than 60 percent of American adults don't exercise regularly and 25 percent of us aren't active at all.

Because the heart is a muscle, its performance improves with exercise. Regular exercise helps prevent heart attack and stroke by lowering blood pressure and low-density lipoprotein cholesterol (LDL, the bad kind) and raises high-density lipoprotein cholesterol (HDL, the good kind). Exercise also makes blood-vessel walls more flexible and, in turn, helps prevent hardening of the arteries. Regular exercise also can reduce your risk for developing diabetes and help keep your weight down.

Before you exercise

You should seek your doctor's advice before starting an exercise routine if you have certain medical conditions, if you have lost weight without dieting, if you have cuts or wounds on your feet that haven't healed, or if you have been inactive for quite some time. The American Heart Association also recommends that you talk with your physician if:

• You're a woman over age 50
• You have a heart condition and your exercise routine should be medically  supervised
• You're taking medicine for your heart or blood pressure
• You get pains in your chest, your neck, your shoulder or arms while exercising
• You've experienced chest pain in the past month
• You tend to get dizzy, pass out and fall
• Mild physical activity leaves you breathless
• You have bone or joint problems
• You have insulin-dependent diabetes or another medical condition that requires  special attention

Once you get approval from your doctor, it's important for you to measure your current fitness level before starting an exercise program. You can figure out your personal readiness, current activity level, flexibility, strength, and aerobic fitness. If you're over 50, also test your balance. Be sure to warm up by stretching before taking any of these tests.

If you haven't exercised in a long time, begin slowly and gradually work up to 20 to 30 minutes of aerobic activity, with rest periods included in the routine. Click here to request a guide on starting an exercise program from the American Heart Association.

Take a walk

If you're uncomfortable visiting a health club, you don't have to exercise in a formal, structured environment. The key to fitness is right outside your door. Walking is the best exercise for many people because it's inexpensive (all you need is a pair of sneakers or walking shoes), convenient (you can do it almost anywhere), and easy.

Studies show that taking a 30-minute walk three to five times each week may reduce your risk for a heart attack. It also may reduce a woman's risk for osteoporosis. In addition, a regular half-hour walk may cut your chances of dying prematurely by two thirds and help you drop up to 18 pounds in a year.

Consider strength training

For people over age 50, the American College of Sports Medicine recommends weight training at least three times each week-in addition to 20 to 40 minutes of aerobic activity and stretching. Weight training, or strength training, is vital because inactive women lose about 10 percent of their lean muscle mass for each decade after age 30. Strength training can help older women build lean muscle mass, strengthen bones and muscles, improve balance, and lower their risk for serious falls.