People who have never raced don’t really understand what they are talking about. When I was 21, I raced a dirt modified. I was in very good physical condition and I was always exhausted after 20 laps. Sometimes, I was breathing as heavily as after running a mile. I was driving a 4,000 lb. car with a 400 HP motor 80 mph entering the turn on a 1/4 mile track. With 20+ cars around me. I promise you, the car does not do all the work. When you are turning a car 180 degrees with turns the same radius as a running track, you are pulling a lot of G’s. Not to mention wearing a 3-layer firesuit, fireproof underwear, neck brace, and helmet in 100 degree temps here in Texas.
I know NASCAR is different, but I can assure you, the above is nothing like getting in the car and running to the mall.
Not to mention the fact that you have to be completely focused the whole time you are racing, whether in a 6 lap heat race or a 500 mile race at Daytona. Focus and adrenaline. Not sure I can think of any other sport that requires that kind of focus for the duration of the event.