(Merriam Webster Dictionary) Definition of an athlete: A person who is trained or skilled in exercises, sports, or games requiring physical strength, agility, or stamina.
When I was competing in my last World Championship (1996 and training for a rematch in 1999), Olympiad (2004) and World Record Simul (2005), I spent at least 6 months or more to train physically every single day. I needed to do this to make sure I have enough stamina toward the end of the match or event.
I also introduced this concept to my teammates at the 2004 Olympiad. World Champions such as Fischer, Karpov, Kasparov, Kramnik and Anand all said that physical fitness is very important to them in high level competition.
Therefore, would high level chess players be considered athletes according to the definition in the dictionary?
Here is a very interesting article about athletes, or not.
Of course world class chess players are athletes.