The Career Athlete is worth 50G and is unlocked by completing an an Olympic Games mode game.

Progress through the Olympic Games mode, which is available to you from the main menu. You will have to meet certain criteria to proceed to the next day. These range from qualifying for an event to winning at least four gold medals out of five events. Should you fail any day it will be game over, however it is not a problem, simply reload and try again. It will take anywhere from 2 hours and upwards depending on how competent you are at the game.