[Not devonin]

Professional chess I'd argue isn't physical at all.

At the extreme top end of Professional Chess, a Super GM will lose nearly 12 pounds over the course of a tournament.

That level of focus, attention, and effort spikes blood pressure, increases heart rate. All of the top players now approach it like a more traditional sport.

They have personal trainers, dietitians, take more care to have downtime between tournaments, it is -very- physically demanding as well as mentally.

Heck, Magnus had a spike in performance by developing a better physical sitting position to put less strain on his neck and shoulders.