Hydration While Riding — What and How Much to Drink
On the bike you lose 0.5 to over 1.5 litres of sweat per hour — depending on temperature, intensity and your own physiology. Just 2% dehydration lowers performance, and 4% is a genuine health risk. Hydrating while you ride isn't optional: it's a condition for good training and for safety. Here's what to drink, how much and when.
How much to drink — a starting point
A general rule: 400–800 ml per hour of riding. That's a wide range, because it depends on:
- temperature — in the heat you need more (up to 1 l/h),
- intensity — intervals generate more sweat than an easy base ride,
- your own sweat rate — some people sweat twice as much as others,
- the trainer — no airflow means more sweat than outdoors at the same power.
The best test: weigh yourself before and after the ride. Every kilogram lost is roughly a litre of water you didn't replace.
What to drink
| Drink | When |
|---|---|
| Water | Rides up to 1 h, low intensity |
| An isotonic drink / electrolytes | Rides > 1 h, heat, hard training |
| A carbohydrate drink | Long, hard sessions (> 2 h) — replaces energy and fluids at once |
On short rides, plain water is entirely enough. On longer ones, electrolytes (sodium, potassium, magnesium) prevent cramps and help with fluid absorption.
When to drink
Don't wait for thirst — thirst appears once dehydration is already under way. The strategy:
- Drink regularly, every 15–20 minutes — small sips, not one big gulp.
- Start early — take your first sip within the first 15 minutes of the ride.
- On the trainer, keep the bottle within reach — it's easy to forget, because there are no natural breaks.
Symptoms of dehydration
- A drop in power at a normal effort,
- a raised heart rate with no rise in intensity (cardiac drift),
- a dry mouth, dark urine,
- headache, dizziness, nausea — these are already serious.
If you notice these signs, slow down, drink and cool off. Continuing to ride in this state risks heat stroke.
Hydration and cramps
Cramps on the bike have many causes (muscle fatigue, intensity), but dehydration and an electrolyte shortfall make them worse. On longer rides, electrolyte tablets in your bottle are a cheap, simple way to reduce the risk.
Summary
Drink 400–800 ml an hour, start early, reach for electrolytes on longer rides, and don't wait for thirst. It's one of the simplest things you can do for your performance and safety — and the difference between a well-hydrated and a dehydrated cyclist is like riding a different bike.
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