# Rehydration after training: why one bottle per hour makes sense

> Making up a fluid deficit takes more than the amount you lost - and gastric emptying depends on fill volume. What rehydration research shows, and why 750 ml is a sensible unit.

Anyone who drinks two glasses of water after a hard session and considers themselves rehydrated is underestimating the physiology. Making up a fluid deficit is not topping up a tank but a process with its own kinetics - and with a number that exceeds the amount lost.

## Why 100 per cent is not enough

Shirreffs and Maughan (1998) had participants drink different volumes after a sweat-induced deficit: 50, 100, 150 and 200 per cent of the weight lost. Only those taking in more than 100 per cent were still in positive balance six hours later. The reason is renal function: a quickly consumed, low-sodium volume dilutes the plasma, suppresses antidiuretic hormone and is largely excreted again.

In practice this means roughly **1.25 to 1.5 litres per kilogram of weight lost**, spread over several hours rather than downed at once. Pace matters just as much: drinking more slowly reduces urine output.

## Sodium decides the balance

Maughan and Leiper (1995) showed the relationship directly: after dehydration they gave drinks with different sodium contents. Net fluid retention rose dose-dependently with sodium concentration. Sodium keeps volume in the extracellular space and sustains thirst instead of switching it off prematurely.

The classic combination of a drink and a salty meal after training is therefore no coincidence - and electrolyte drinks beat plain water after large sweat losses.

## Gastric emptying depends on volume

A second regularity applies to drinking **during** exercise. Mitchell and Voss (1991) showed that the gastric emptying rate rises with the fill volume. A well-filled stomach empties faster than a nearly empty one - sipping in small amounts slows your own absorption.

The counterforce comes from composition. Vist and Maughan (1995) demonstrated in the Journal of Physiology that carbohydrate content and osmolality slow emptying: the more concentrated the solution, the longer it stays in the stomach. Both together give a workable pattern: 150 to 250 ml of a moderately concentrated solution every 15 to 20 minutes - roughly 600 to 750 ml per hour in total.

## How the WOO® BioBased Trinkflasche 750ml (Schwarz/Gold) puts this into practice

This arithmetic explains why 750 ml is a practical unit: one filling corresponds roughly to one hour of intake under load. That turns a drinking strategy into something you can run without counting - one bottle per hour, in regular portions rather than single sips. The same logic applies to rehydration afterwards: with one kilogram lost, about two fillings across several hours is the target.

The **[WOO® BioBased Trinkflasche 750ml (Schwarz/Gold)](/en/shop/woo-biobased-drinking-bottle-750ml-black-gold)** is made from bio-based materials, is food-safe, dishwasher-proof and fully recyclable. With carbohydrate drinks, dishwasher-proof is not comfort but hygiene: sugary residues in a moist container are a growth medium. The larger capacity pays off above all on long sessions and outdoor activities where refilling is not always possible.

## Frequently asked questions

**How much should I drink after training?**
About 1.25 to 1.5 times the weight lost, spread over several hours. One kilogram less on the scales corresponds to roughly 1.25 to 1.5 litres.

**Is water enough for rehydration?**
For small losses, yes. After heavy sweating, sodium - from the drink or from the next meal - markedly improves fluid retention.

**Is it better to take small sips?**
During exercise, not necessarily: a higher stomach volume accelerates emptying. Regular portions of 150 to 250 ml are more efficient than constant sipping.

## Sources

Shirreffs SM & Maughan RJ (1998), Medicine & Science in Sports & Exercise - Volume repletion after exercise-induced volume depletion in humans: replacement of water and sodium losses.
Maughan RJ & Leiper JB (1995), European Journal of Applied Physiology - Sodium intake and post-exercise rehydration in man.
Mitchell JB & Voss KW (1991), Medicine & Science in Sports & Exercise - The influence of volume on gastric emptying and fluid balance during prolonged exercise.
Vist GE & Maughan RJ (1995), Journal of Physiology - The effect of osmolality and carbohydrate content on the rate of gastric emptying of liquids in man.

*WOO® BioBased Trinkflasche 750ml (Schwarz/Gold) - available in our shop.*