The body is in a constant state of dynamic equilibrium

The body is in a constant state of dynamic equilibrium, in which fluids are shifting back and forth for redistribution to where they are needed. And the body maintains a strict limit on how much it will allow us to change these volumes and concentrations to prevent serious loss of function.
The body desperately tries to maintain the exact volume in all 3 of the interior spaces. It is crucial to find ways to support that effort when our activities cause even minor shifts. The body will compensate, but it won’t be at its most efficient until it’s back in balance.
Before starting an activity, avoid having a lot of water inside your stomach; start drinking water a couple of hours before the activity so that you are able to spread out the absorption and fill all your body spaces to capacity.
The body always wants to return to that balanced internal milieu. For normal athletic events and outings in moderate temperatures and altitudes, it should be enough to hydrate slowly over several hours and be able to perform well without further input.
Myth: Athletes should avoid caffeine, because it is a diuretic. Caffeine is a very weak diuretic, but there are better ways to hydrate than with a caffeine-containing drink. If you do drink something containing caffeine, you will probably get more fluid from the drink than you will lose from the caffeine.
Myth: Bottled water is the purest, safest, best-tasting source of water. Bottled water is not necessarily purer, safer, or better tasting than tap water in most cities throughout the industrialized world. If the taste of your local water bothers you, try a carbon filter or reverse-osmosis filter on your faucet.
Important Terms
Diuretic: something that stimulates increased urine output.
Dynamic equilibrium: where fluidsare shifting back andforth for redistribution to where they are needed at any specific time and for maximum efficiency.
Rough guidelines for rehydration before, during, and after exercise are outlined below. Remember that you will need to individualize these guidelines by careful trial and error, measuring your intake, urine output, weight, and time periods of activity.
Break your water fast when you wake up in the morning. You don’t want to start the day dehydrated. In the 2-3 hours before you begin your exercise or competition, drink about a quart and a half of water or sports drink. It takes about an hour
for a quart and a half of water to leave the stomach andfind its way to tissues, especially to muscle.
During your exercise period, aim for about 10-15 ounces every 15-20 minutes for the duration of a long, hard workout.
If the exertion is longer than an hour, you may need to add something more than water, including a drink with about 10% carbohydrates-simple sugars are best-and sodium at about .5 to .7 g/L.
After exercise, you should measure your weight loss and replace nit by 150%. By weighing yourself, you will be measuring all the water lost though metabolism, sweat, and obligatory urine loss. If you lose a pound of weight (almost all water) you need to replace nit with 1.5 pounds of water or 24 ounces. As a backup, weigh yourself again after you think you have replaced all the water loss, nand correct any discrepancies.