Over the years, you've probably filled a number of prescriptions to help you get better or stay healthy. The most important one — which you may never have been given and can't fill at any pharmacy — is for exercise.

Exercise? It's far better than any pill or potion for lowering your risks for heart disease, diabetes, stroke, high blood pressure, depression, some forms of cancer, and other serious health problems. Exercise can ease arthritis, preserve independence, keep you trim, and improve your sleep. In short, exercise can help you feel better, look great, and live a longer, more joyful life.

How active do you need to be to reap these gains? Not as much as you might think, according to Exercise: A program you can live with. This Special Health Report from Harvard Medical School recommends burning at least 500 to 1,000 calories a week through exercise. That translates into at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous activity (or a mix of the two) every week. It's also wise to add in some exercises to strengthen arm and leg muscles.

Sometimes it's hard to start exercising. "Getting in gear," a special section in Exercise: A program you can live with, offers tips and tools for creating a personal exercise plan that covers all the bases and fits your life and lifestyle. If you currently exercise but find yourself skipping it more and more often, the report offers ways to keep yourself motivated.

Also in this report:

• How exercise affects the body
• Exercising safely
• Choosing the right exercise equipment
• Strength and stretching routines

You can read a free excerpt from the report about ways to keep exercise fresh on the Harvard Health Publications website.