Soccer legend Lionel Messi announced Monday his retirement from representing Argentina in international play. As the first player to win the World Cup twice, the 39-year-old tried his shot at a third win this summer, but left empty handed. Advances in training, recovery and sports science are allowing elite athletes to compete longer than ever, but the psychology of when to hang up the towel also plays an important role. The World’s Host Marco Werman learned more from Helena Hlasová, a researcher at the University of Bern’s Institute of Sport Science.