i get that information from trainign and doing major length events
In my ironman I had an exact number for calorie intake and water intake, and sodium, and pottasium, and magnesium, and and calcium, and obvioulsy carbs and protien.
As an example- when you come out of a 2.4 mile swim you are NOT thirsty, but you are already starting to dehydrate. As youo start on your 112 mile bike you need to "water and electrolyte up" big time.
On top of that, if you are riding that 6-8 hours on the bike in cool wherther you will not feel thirsty, but you better drink or when you get off that biekl to run 26.2 miles another 4 - 6 hours yoou will cramp immediatley if you have not been eating and drinking.
In my iornman event I ate over 15,000 calories, over 10 grahms of sodium, etc etc etc.....
drank at least 24 oz's per hour, and at the end I had lost 9 lbs, within 13 hours.
well 12:27:43 to be exact!
Now homeboy - you got your information from where again? LOL!
This is the reason FF is my trainer ... he knows his ish