By June SimmsFrom VOA Learning English, this is Science in the News. I'm Bob Doughty. And I'm June Simms. Today, we will tell why exercise is so important. And we will tell about some popular ways to get in good shape.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.America's Centers for Disease Control and Prevention says heart disease is the leading cause of death in the United States. About 600,000 Americans die of heart disease every year. 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.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. In 2008, 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 was that some activity is better than none. So if you are not doing anything, now is the time to get started. CDC officials define 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 lifting weights, or doing sit-ups and push-ups.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 15 minutes. Some examples are playing basketball, swimming and distance running.Earlier advice from the CDC said that people need to exercise at least 30 minutes each day for at least five days to get the health benefits of exercise. More recent research has suggested that those gains are the same whether you exercise for short periods over five days or longer sessions over two or three days.In addition, the newer suggestions say any exercise plan should include at least two days of muscle training. Each exercise period should be at least 10 minutes long. The total amount of activity should be spread over at least two days throughout the week. Most importantly, experts say people should choose physical activities that they find fun. This helps to guarantee that they stay with the program.So, what are some of the most popular forms of exercise in the United States? Walking tops the list. A 2012 report from the CDC found that more than 145 million Americans now include walking to stay physically fit. For many people, it is considered the easiest way to get exercise. It does not require a health club membership.Walking is safe. And, it is said to be as valuable for one's health as more intense forms of exercise like jogging. Walking is also said to be less damaging to the knees and feet. This makes it a better choice of exercise for older adults. Another popular form of exercise is jogging, or running at a slow to medium speed.USA Track and Field Hall of Famer Bill Bowerman was credited with bringing jogging to the United States in the 1970s. He did so after witnessing the popularity of the activity himself during a trip to New Zealand in the 1960s. He started the first running club in America and wrote a book about jogging for fitness. Bill Bowerman also helped establish Nike, the tennis shoe company.Jogging provides great physical conditioning for the heart and lungs. And, it increases the flow of blood and oxygen in the body. All of these things combined help to improve heart activity, lower blood pressure and cholesterol levels, and reduce bone and muscle loss. Running is also a good way to lose weight. People burn an average of 160 calories a kilometer while running.The Census Bureau says swimming was the fourth most popular sports activity in the United States in 2009. The top activity was exercise walking, followed by exercising with equipment and camping. Swimming is said to be one of the best ways to exercise. Nearly all of the major muscle groups are put to work.Swimming also presents less risk of muscle and joint injury because of the body's weightlessness in water. This makes it a great choice of exercise for people with special needs, like pregnant women, older adults, and persons who are overweight. Some people have questioned whether swimming burns as many calories as other forms of exercise. But one thing is sure: the effects on your health are just as great. Water aerobics is another popular form of exercise. This can be anything from walking or running against the resistance of water, to doing jumping jacks in the water.Dancing can also be a fun way to exercise. This is especially true for those who see exercise as a necessary evil: something they should do, not something they want to do. A dance-fitness program called Zumba has grown in popularity in recent years. Zumba is said to be one of the fastest-growing group programs in the physical fitness industry today. Alberto Beto Perez created Zumba in his native Colombia in the 1990s. His dance-fitness program is based on salsa, meringue, and other forms of Latin American music.Mister Perez brought the program to the United States in 2001. Since then it has spread around the world. The Zumba website says its classes are now offered in 140,000 gyms, fitness studios and dance clubs around the world. That is up from about 2,000 locations in 2006. The website also says that 14 million people now attend Zumba classes in 151 countries.Whatever kind of exercise you choose, experts agree that you should start small and work your way up. Start by exercising 10 minutes a day two times a week. After a few weeks, increase your time to 15 or 20 minutes, and increase the number of days. Next, aim to increase the intensity of your workout. If you have been walking, trying walking faster, or take turns between walking and jogging. And try not to forget those muscle strengthening exercises.The more time you spend exercising, the more health benefits you get. Health experts advise people who have been physically inactive to have a complete physical exam before beginning a new exercise program. If one of the goals of your exercise program is to lose weight, you will also need to change how and what you eat. Next week we will look at the influence of diet on your weight loss efforts.This Science in the News was written and produced by June Simms. I'm Bob Doughty. And I'm June Simms. Join us next week for more news about science on the Voice of America.