Lance Armstrong retired from cycling in 2005 after winning seven consecutive Tour de France. Then he would make the mistake of returning in 2009, which would end up "forcing" the USADA to investigate him and the rest was history. Recently when taking up a marathon his experience ended in disaster.
If Michael Jordan was into baseball, Armstrong was into racing, and he did it. He prepared thoroughly and competed in the 2005 New York Marathon, which he considers the hardest race he has ever run: "Going under three hours in the New York Marathon was the hardest thing I've ever done in my life.