What does Chris think about when he's running to help motivate him?

Chris motivates himself with a desire to beat the family dog.

“Buckley was supposedly my dog,” says Carine, “but he and Chris became inseparable. Buck was fast, and he’d always beat Chris home when they went running. I remember Chris was so excited the first time he made it home before Buckley. He went tearing all over the house yelling ‘I beat Buck! I beat Buck!’”