In "How to Transform," why does the narrator decide to give up going to the gym?

After going to the gym for two weeks and never getting to play, the narrator finally decides to stop going altogether. He tells his father he will not be riding with him the next morning. His father only chuckles. The next morning he wakes up at his usual early time -- his body has gotten so used to getting up. So he decides to go back to the gym. When his father sees him waiting at the car, once again he only chuckles.