Try to increase the intensity of your workout. If you have been walking, try walking faster, or take turns between walking and jogging. And don't forget muscle strengthening exercises.

    FAITH LAPIDUS: This is the VOA Special English program SCIENCE IN THE NEWS. I’m Faith Lapidus.

    BOB DOUGHTY: And I’m Bob Doughty. Today, we will tell about physical exercise. We will tell why exercise is important, and some of the popular ways to get in shape.

    FAITH LAPIDUS: Summer officially returns to the United States in less than two weeks. For many Americans, summer is a time to put on swim wear and spend time at the sea or a lake. But before going anywhere, they may want to lose any extra weight gained during the winter.

    So, where does one get started? Diet is surely important, but diet alone will not do much good without an exercise plan. Health experts have long noted the importance of physical activity.

    Exercise not only improves your appearance. It can also improve your health. Exercise helps to reduce the risk of some diseases. They include heart disease, stroke, type-two diabetes, osteoporosis and even some kinds of cancer.

    BOB DOUGHTY: The Centers for Disease Control and Prevention says heart disease is the leading cause of death in the United States. In two thousand six, heart disease killed more than six hundred thirty thousand Americans. High blood pressure and high cholesterol levels in blood can increase your risk of heart disease. Medical experts say both can be reduced through normal exercise.

    Physical activity is also known to increase the release of endorphins. These chemicals reduce feelings of pain. They also help people feel more happy and peaceful. There is some debate about exactly what causes the brain to release endorphins. Some experts believe it is the act of exercising itself. Others say it is the feeling one gets from having met an exercise goal. Either way, the two things work together when it comes to improving one’s emotional health.

    FAITH LAPIDUS: Surprisingly, exercise improves your energy levels by increasing the flow of blood to the heart and blood vessels. One of the main reasons people exercise is to control or reduce their weight. Physical activity burns calories – the energy stored in food. The more calories you burn, the easier it is to control or reduce your weight.

    So exactly how much exercise do you need to do to gain all of these great health effects? Experts say it is easier than you think. Two years ago, the Centers for Disease Control released its first ever Physical Activity Guidelines for Americans. The report included suggestions for young people, adults, disabled persons and those with long-term health problems. One of the major ideas noted in the report is that some activity is better than none. So if you are not doing anything, now is the time to get started.

    BOB DOUGHTY: The C.D.C. defines physical activity as anything that gets your body moving. And, it says there are two separate, but equally important kinds of physical activity. Aerobic or cardio exercise gets your heart rate going faster and increases your breathing. Some examples are activities like walking at an increased speed, dancing, swimming or riding a bicycle.

    Muscle-strengthening activities help build and strengthen muscle groups in the body. This kind of exercise includes things like lifting weights, or doing sit-ups and push-ups.

    FAITH LAPIDUS: To get the most from your exercise plan, experts say adults should get at least two and a half hours of aerobic exercise each week. More intense activities reduce the suggested amount of time to one hour and fifteen minutes. Examples are playing basketball, swimming and distance running.

    Earlier advice from the C.D.C. said people need to exercise thirty minutes each day for at least five days to get the health benefits of exercise. More recent research suggested that those gains are the same whether you exercise for short periods over five days or longer sessions over two or three days.