Full stats
At the main menu, quickly press Left(2), Right(2), Up, Down, Left, Right, Left. If you entered the code correctly, you will hear a sound. Select "Olympic" mode to have full statistics in all events.
Gold medals
At the main menu, press Circle, X, Triangle, Square.
First in all events
At the main menu, press Triangle, Square, Circle, Square, X.
Gold in Javelin event
At the event selection screen, press Circle, Square, X(2).
Gold in Sprint event
At the event selection screen, press X(3), Circle, X(3).