How does Charlie’s running become transformed into something positive in this chapter?

Charlie comments that he is getting faster with Mr. Redmond’s training schedule. Twice a week they take the tram to St. Kilda beach so Charlie can sprint barefoot in the soft sand. People watch and jeer at him, but the attention and teasing only make him more determined. He welcomes the burning pain in his legs. Charlie is developing a positive sense of identity and drive that he never had before.