9781422287019

Research Project The sidebar in this chapter says that our life expectancy—the number of years we can expect to live—has increased in recent years. Use the library and Internet to f ind out how life expec- tancy has changed over human history. Discuss how exercise does or doesn’t play a part in extending most of our lives today. Do we exer- cise more or less than people did f ifty and a hundred years ago?

EXERCISE Exercising is a good way to keep the metabolism moving, and it is also the only way to strengthen the body’s muscles. Some of the muscles helped through exercise are skeletal muscles, such as the ones found in the legs and arms. It is easy to see how exercise helps these muscles, because they grow bigger over time. However, there are other muscles that need to be worked out that cannot be seen.

Make Connections Just one hundred years ago, the average human was expected to live less than f ifty years. Average life expectancy has increased by at least twenty-f ive years since then. One of the reasons is the improvement of modern medicine. Because we know how to

treat disease, people are less likely to die from it. Scientists have also learned a lot about what a human being needs to live a long, healthy life. Regular exercise is one of the key components to extending human life.

Sports & Fitness

12