Bottoms Up! Hydration for the Ride You Are Doing

Drink for the ride you are doing

Start the ride hydrated, drink enough that you do not lose more than about 2 percent of your body weight, use a drink with electrolytes on long or hot rides, and do not force down more than you lose. The best way to know your number is a bathroom scale, before and after.

We preach this one constantly, and we do not always follow it. When the first version of this post went up in 2016, the person writing it admitted he was kicking himself for not taking his own advice. Drinking enough sounds like the easiest thing in cycling, but somehow it slips anyway.

So here is the reminder, built on what the American College of Sports Medicine actually recommends instead of a list of magic numbers.

Why it matters on the bike

Muscle is about three quarters water. A 2019 review in the journal Nutrients puts it at roughly 76 percent, which makes muscle the main water reservoir in the body, so your legs are mostly the stuff in your bottle.

When you ride, you sweat to shed heat, and that water and salt have to come from somewhere. ACSM's position stand on exercise and fluid replacement says the goal of drinking during exercise is to keep you from losing more than about 2 percent of your body weight to dehydration, and to avoid big swings in electrolytes, so your performance does not suffer.

There is no one right number

The old version of this post had a neat list of ounces before, during and after, and we cut it. ACSM's whole point is that sweat rates and sweat salt vary a lot from one rider to the next, so it recommends a plan built around you, not a number off the internet.

The good news is that finding your number takes a scale and one ride.

1. Weigh yourself before the rideSame scale, minimal clothing, after using the bathroom.
2. Ride for an hour and track what you drinkCount the bottles, and a full 22 ounce bottle makes the math easy.
3. Weigh yourself again afterTowel off first. A sweat-soaked kit can hide some of what you lost.
4. Add it upWeight lost plus what you drank is roughly your sweat loss for that hour, in those conditions.

Here is a made-up example: a rider weighs 1.5 pounds less after an hour and drank one 22 ounce bottle. A pound of water is a little over 15 fluid ounces, so 1.5 pounds is about 23 ounces. Adding the 22 he drank, he sweated roughly 45 ounces that hour, so one bottle was nowhere near enough. Next time, in the same weather, he knows to plan on two.

Run the test in a few different conditions, like a cool morning and a hot afternoon, and you will have a real sense of what you need. A 2017 review on sweat testing by Lindsay Baker of the Gatorade Sports Science Institute calls body weight change the simplest and most accurate way to measure whole-body sweat rate, as long as you account for what you drink and any bathroom stops.

Before, during, after

1. Before: start hydrated. ACSM says to drink, when needed, at least several hours before you ride, so your body has time to absorb it and get rid of any extra.
2. During: drink to stay under that 2 percent loss. On long or hot rides, a drink with electrolytes and carbohydrate can beat plain water, according to ACSM.
3. After: replace what you lost. How fast you need to depends on how much you lost and when you ride next.

Too much is a real problem, too

The old post left out the fact that you can overdo it.

A 2015 international consensus statement on exercise-associated hyponatremia, published in the British Journal of Sports Medicine, says the main cause is drinking more fluid than you lose, which dilutes the sodium in your blood. It also says that almost all cases with symptoms have happened in people who gained weight or held steady during exercise. Their recommendation for most athletes is to drink when thirsty, and they say drinking to thirst will, in most cases, prevent it.

If you weigh more after the ride than before, you drank too much.The same scale test that catches under-drinking catches this, too.

So the scale works both ways: a small loss is normal, and a gain means you should back off.

The toilet check

The old post had one tip worth keeping: look at your urine.

That one has research behind it. A 1994 study at the University of Connecticut found urine color tracked closely with lab measures of urine concentration, and concluded it works fine in the field when a close estimate is good enough. It is not a lab test, but it is a decent daily gut check.

What goes in the bottle

For an hour of easy riding in cool weather, water is fine. For longer rides, hotter days, or salty sweaters (you know who you are, look at your kit after a ride), we would reach for something with electrolytes.

Skratch says its Hydration Sport Drink Mix was created to replace the electrolytes lost in sweat and provide a little energy. SiS HYDRO tablets drop into a bottle when you want electrolytes without the calories. If you are going long, you need two bottles and two cages, and a Tacx Deva cage holds a bottle without a fight. Everything else is in our drink mixes and water bottles sections.

Stay hydrated, my friends, and go ride your bike.