An interesting question. This is not science so there will never be a perfect answer. I tend to disagree though with the overall direction of this story. Training for months for a marathon doesnt' make one an athlete. I used to run several times a week, and I ran marathons in the past. No way I was an athlete. In the last couple of years I took my hobby of running to a new level and now I do consider myself an athlete. As I'm trying to think about this, I think it's a combination of things. You have to be very good at your sport, even as an amateur (I'm yet to run a major marathon but I did win my age group in a local California marathon and I think I can improve a lot, if I avoid injuries). You have to do your sport every day, even as an amateur. EVERY. DAY. In fact, sometimes more than once a day. That's what most pro athletes do (save for some rare rest days or offseason stretches that are intentionally planned). You have to build your life around your sport, like you build your life around your family or work. That's not necessarily a good thing by the way, but if you are athlete you prioritize your sport. You have to think holistically about striving for excellence at your sport - so nutrition, recovery, etc. So all these factors. Again, there is no right answer. Everyone is welcome to consider themselves an athlete but I do think there are differences between true athletes and fitness enthusiasts