Everyone hopes to live happily in the world. Physical exercise is indispensable to a happy life. There is a famous saying: "Life lies on exercise." Although you will not necessarily die without regular physical exercises, they' II certainly help you live longer and more healthily.

Exercise is good for us to build our bodies. It helps co - ordinate the different parts of our bodies when we have sports. For example, we must try our best to co - ordinate the movements of the arms and legs when we play basketball, or we won't be able to shoot the basket. Exercise also benefits our organs. It lets the heart beat faster than usual, and then helps enlarge the blood vessels to protect us from heart attacks. 

Exercise can also contribute to the development of our ability to response agilely. For instance, when you play table- tennis, you must try to reflect as quickly as you can so that you may fight back at the right position at the fight moment. 

Exercise can also contribute to improving our mood. When you do exercise, you move a lot, and you have to be more active. It helps you become more optimistic.

Exercise will fill your life with various contents and make it more colorful.

What's more, exercise will help you get rid of your inertia. If you keep doing exercise regularly, you will never be a lazy person. Therefore, exercise has great effect on one's character.

 In a word, exercise is helpful, important and absolutely necessary.