It seems that physical activities inevitably ______, which improves fitness.

Getting in Shape
Interviewer: Ralph, we know that you have done some of the largest studies on exercise and health. Would you like to give us some tips on how to exercise and keep fit?
Ralph: I would be glad to.
Interviewer: I have been doing what I can to stay healthy. But some of my friends they are mostly young and healthy couldn’t care less. They say they are doing fine without exercise. Is regular workout really that important?
Ralph: Sure it is. If one doesn’t exercise regularly, he’s missing out a lot. A person who is inactive may increase his chance of disease. For one thing, he may have sleep problems or easily catch a cold, to say the least. And obesity is often the result of lack of exercise. So high blood pressure or heart problems may develop as he grows old. On the other hand, if one adds regular activity to his life, he is sure to benefit.
Interviewer: What are some of the benefits, can you tell us?
Ralph: Yes. If you work out regularly, studies suggest, you’ll reduce your risk of heart attack, cancer, and high blood pressure. You’re likely to extend your life with vigorous exercise. Even moderate exercise half an hour of light physical activity most days will lessen your chance of disease. Besides, regular workouts, regardless of intensity, can help you control stress, anxiety, and depression.  Interviewer: Hmmm... That sounds amazing. No wonder I will feel restless if I omit one or two sessions when I am too busy. But another question is, what types of exercise are there to keep fit?
Ralph: Basically, there are four types of workout that help us get in shape. The first type is cardiovascular exercise. This exercise helps strengthen the heart by working it harder. Swimming, running, brisk walking, vigorous rowing, or just anything that you need to exert yourself to do to burn calories and make the heart beat faster. Eventually, your heart becomes more efficient and your pulse rate will be slower at a given level of exertion.
Interviewer: Like an athlete, you mean?
Ralph: Exactly. But an athlete strives to do his best to come out first, while we want simply to stay healthy.
Interviewer: Right. What about the second type?
Ralph: The second type is endurance exercise. That trains the heart, lungs, and muscles to work hard for a longer time. Thus, while regular 20minute walks may help you live longer, regular one-hour walks can help you play longer. The third type is strength training, which builds muscles. The improvement is little felt and fleeting at first, but regular use of the same muscles eventually increases their size and strength.
Interviewer: You mean like those body-builders who have got enormous and beautiful muscles?
Ralph: Not exactly. Strength training isn’t just for the vain; having stronger back and abdominal muscles, for example, supports your spine, making back trouble less likely.
Interviewer:  I see.
Ralph: The fourth type is flexibility exercise, which keeps muscles long and supple, so they’re less likely to be injured.
Interviewer: Do we have to engage in all those forms of exercise in order to stay in shape?
Ralph: Not necessarily. It all depends on your need, and also age. Younger people could engage in more vigorous activities or deliberate workouts, while the older people could just try anything that burns a little more calories, like walking or even gardening. The word "exercise" can be quite loosely defined. It can include out-of-the gym activities such as lawn-mowing, leaf. raking or even cleaning the house. Just about any amount of physical activity will improve fitness.
Interviewer: Then when should one begin? Say someone has been inactive for years, is it too late or is he too old to exercise? Could he change his way of living by working out a little right away?
Ralph: Absolutely. One could get started at any time, any age. The greatest benefit of exercise may come at the beginning, when you jump from doing nothing to doing something. At the beginning, you just try a little. Walk a few more steps: Every day, park the car a few blocks from work. Don’t use an elevator when you can walk. Don’t use the phone to ask colleagues questions; walk to their offices. At home, don’t use the car for nearby errands. Walking the dog, playing catch with the kids, gardening, mall-walking all count as exercise.