A、too much exercise often leads to a shorter life span B、American football is too violent to be good for one’s health C、to exerc

Woman: Dr. Mirkin, doctors seem to put a lot of emphasis on exercise. Is exercise really so important to the health of an average person?
Man: Yes, it is. Exercise is important not only for the health of your body, but for your mind.
Woman: How does exercise help one’s mind?
Man: A person’s mood is helped significantly by exercise. There are many physicians who prescribe exercise for those people who don’t feel very good about themselves. Exercise is effective as a tranquilizer. Tests have shown that a 15-minute walk can have a more tranquilizing effect than the most-used tranquilizers on the market today. It has been demonstrated that people who exercise suffer less from anxiety and are able to work harder. Lack of physical fitness is often associated with decreased performance at work or in school. One study showed the 83 percent of the freshmen who flunked out the University of Syracuse were in bad physical shape. Conversely, student at Nathaniel Hawthorne Junior High School in Yonkers, N.Y., who were failing were put into a physical fitness program, and their grades picked up. So did their behavior. Exercise also helps you sleep at night.
Woman: What are the chief physical benefits of exercise?
Man: Physically, the most important value of exercise is the way it trains your heart. Students have shown that people who continue to exercise late into adult life live longer and are less likely to die from heart attacks. This is contrary to what people were taught years ago. But it is not how much exercise you get when you are older that’s important. A study showed that Harvard football players died younger, on the average, than their nonathletic counterparts.
Woman: For a person who’s not an athlete--and never has been--what kind of exercise should one do in adult life?
Man: The best kind of exercise is one that trains your heart. To do that, you must get your pulse up to 120 beats per minute for at least 30 minutes and at least three times a week. Any sport that doesn’t do that doesn’t really Wain your heart as it should be trained.
Woman: What do you mean by training the heart?
Man: The heart is like any other muscle--the more your exercise it, the larger and stronger it becomes. A large, strong heart doesn’t have to beat as often to do its work, so it will take longer to wear out. There are other benefits to the heart from exercise. A heart attack is usually caused by an obstruction of the blood vessels on the outside of the heart that supply oxygen to the heart muscle. When you exercise regularly at 120 beats a minute, you enlarge those blood vessels. There’s a type of fat in the blood called low-density cholesterol that many authorities believe is associated with heart attacks. Exercise lowers the amount of low-density cholesterol. Heart attacks may be associated with stress, and studies show that exercise decreases your feeling of stress. It also lowers blood pressure, which is another risk factor in heart attacks.
Woman: Specially, what exercises are best to train the heart?
Man: The sports that are most highly recommended include bicycling, running, jogging, ice skating, roller skating, jumping rope and cross-country skiing. If you can’t go outside, bicycling can be done indoors on a stationary bicycle, and you can do your jogging in place or on a treadmill, qbe bad thing about such stationary exercises is that they can be boring. You should enjoy exercise. But the important thing is to bring your heartbeat up to at least 120 beats a minute. It may surprise you that tennis is not an ideal sport to train your heart--mainly because its action is not continuous. For training your heart, it would take 2 hours of tennis to equal 15 minutes of jogging. Golf is a poor sport for training your heart. So are bowling, walking and weight lifting.
Woman: How about swimming?
Man: Swimming is an excellent exercise if you swim long enough--at least 30 minute each time--and energetically enough. My advice is when swimming to keep as much of your body as possible in the water, and in stroking to get your hands back into the water as fast as you can.
Woman: Is dancing a good exercise?
Man: Aerobic dancing is an exercise. I recommend it for women, because most women don’t like ordinary exercise but like to dance.
Woman: What about disco dancing?
Man: Disco dancing is excellent. If you see young people dancing in a nightclub or discotheque today, you’ll see they are really training their hearts because there is no way they can do that kind of dancing and keep their pulse rates under 120. Square dancing can also be excellent--provided that it’s done continuously and vigorously.
Woman: How late in life should a person do such exercise?
Man: There is no age limit.
Woman: Isn’t it dangerous for some people to exercise as vigorously as you recommend?
Man: Everyone over 35 should get a stress electrocardiogram--to find out how his or hex heart will be have with vigorous exercise. An ordinary electrocardiogram---the kind you usually get in a doctor’s office---only tells you how your heart behaves while you are resting. So ask your physician to measure your heart while you exercise. This will not only tell, with a large degree of probability, whether your heart is sound, but will also indicate how much exercise your heart can tolerate safely and the maximum pulse rate that is safe for you.