Andrea Kuszewski in Scientific American:
Chess-boxing is divided into eleven short, rapidly rotating rounds—six four-minute rounds of speed chess, alternated with five three-minute rounds of boxing. Winning is achieved by KO, checkmate, or in the case of a draw, points determine the winner.
The idea of performing at such a high physical level (boxing) as well as a high mental level (chess) seems arduous enough. But it isn’t just the physical effort plus the mental effort of the two sports combined that makes it especially daunting—it’s the constant alternating back and forth between the two that’s the real challenge.
What is it about the alternating rounds that make this so intensely demanding? Interestingly, the answer lies largely in emotion regulation. The strength of a world-class boxer, and the high rank of a chess player are of no use if a player lacks the one all-important skill—his ability to effectively regulate his emotions in order to maintain cognitive control.