Robert Sapolsky, who studies stress in primates at Stanford University, says a chess player can burn up to 6,000 calories a day while playing in a tournament, three times what an average person consumes in a day. Based on breathing rates (which triple during competition), blood pressure (which elevates) and muscle contractions before, during and after major tournaments, Sapolsky suggests that grandmasters' stress responses to chess are on par with what elite athletes experience.
"Grandmasters sustain elevated blood pressure for hours in the range found in competitive marathon runners," Sapolsky says.
It all combines to produce an average weight loss of 2 pounds a day, or about 10-12 pounds over the course of a 10-day tournament in which each grandmaster might play five or six times. The effect can be off-putting to the players themselves, even if it's expected. Caruana, whose base weight is 135 pounds, drops to 120 to 125 pounds. "Sometimes I've weighed myself after tournaments and I've seen the scale drop below 120," he says, "and that's when I get mildly scared."
