How Much Fluid Do I Need on Race Day?

So replacing 125 to 150% of fluid losses over the next four hours. Of the fluid deficit, not the fluid loss. So yeah, you might have lost two liters of fluid during the session. But if you drank one and a half, the deficit's only half a litre. And it's a building that kind of picture of what your expected fluid losses are going to be from multiple tests is really where I see the value in that kind of data as opposed to the one off.