Originally Posted by
WhyFi
Man. I drank 6 bottles of water/sports drink on the bike yesterday (it wasn't hot, the sun wasn't beating down and I was at an endurance pace) and drank another 5 or so glasses of water in the evening... and I still weighed in more than 3 lbs lighter than yesterday.
You have three fluid compartments to fill. The first is circulating plasma; the second is the interstitial space (in tissue between cells); and the third is intracellular. Transfer from compartment to compartment, particularly from interstitial to intracellular is slow. You can dilute your plasma and piss like a race horse while your cells are still dehydrated.
Then there is the weight of muscle and liver glycogen and the water bound in its crystalline structure. That can take a day to replenish too.