One possible version:

     My hobby is doing sports. I used to be a little weak. Now I'm strong because of doing sports.

     So I became interested in different kinds of sports, such as running, swimming and playing ball games

and I kept exercising at least half an hour a day. I was getting healthier and healthier.

     Whenever I feel tired or stressed out, I do sports. That can make me relax and feel happy. Then I can

study better. Doing sports is really a great hobby.