Discipline is what you use when you don't want to do something, when you have to force yourself.
Do you have to discipline yourself to have breakfast, lunch or dinner? Of course not; and so discipline - the usual concept of it - doesn't apply here. I had to discipline myself to learn English, but never to train.
People say, My God, you're so disciplined. But it has nothing to do with discipline; I loved it. Because I knew that every time I went to the gym I was one step closer to winning the competition.