Specifically to racing, the drivers are in full concentration. It's not just riding in the machine, they've got to feel the feedback through the car to intuitively know the limits of the grip dynamics and judge their pace, pay attention to the racing line not just for themselves but also to not crash, hover in the slipstream for the right moment, deviate from that line to block. Yes, for hours, in a cramped, sweltering, and uncomfortable box on wheels.

And that's just race day. That's not counting practice.

It may not be physically taxing in the way a foot race might be, but it's absolutely taxing.