In typical summer races drivers lose 4 to 8 pounds during a race. It is a very physically demanding job. I am by no means a driver but I have been behind the wheel a time or two. Going down the straight away is like holding to bricks in your hands at chest level. Unless you are in great shape, one lap will leave you sore and exhausted. And we aren't even talking about trying to take the turns which is a whole different animal.