Everything You Needed to Know About Hydration

Everything You Needed to Know About Hydration

Lisa Jhung
Writer and Author of Running That Doesn't Suck: How To Love Running (Even If You Think You Hate It)
March 11, 2024

Summer’s coming. And with it comes an increased need to hydrate both before, during, and after your runs.

Yes, hydration is important even when it’s cold outside. But when the temperature heats up, becoming dehydrated on a run puts you at the risk of heat exhaustion and other complications. The CDC put out a guide to staying hydrated while at work (not on a run), intended for those who do physical labor (which, we all know, running is a physical labor of love!).

The guide does a good job laying out hydration needs visually and can be found here.

Specifically for runners, here’s the lowdown on what you need to know:

Pre-hydration is Both Possible and Important

You don’t start a road trip with an empty tank of gas. For the same reason, it’s important to pre-hydrate, both in the hours before your run and the night before. In fact, staying hydrated is the best thing you can do for yourself. Water is good for you skin and your overall system, and always topping off will ensure you’re hydrated when you do exercise.

The More You Sweat, the More You Need to Drink

This may seem obvious, but it’s true. Your sweat rate determines just how much fluids you need to put back in your body when you run, while you run. How can you determine your sweat rate? There’s a scientific way to do it, and a not-so scientific (but effective) way.

The scientific method requires weighing yourself, completely naked, during a run (X). After your run, weigh yourself naked again (Y). Take the X, subtract Y. Add how many fluids you drank during the run, and subtract how many ounces you peed during the run. If you don’t want to capture your pee in fluid ounces and do complicated math, simply weighing yourself before and after a run can tell you if you need to hydrate more. If you weigh less after your run, you do.

The non-scientific method of calculating your sweat rate is this: if your pee is clear or very light yellow, you’re hydrating well. If it’s darker than light yellow, you’re not.

How Much You Drink on a Run is a Personalized Matter

A 2022 study published in the International Journal of Sport Nutrition and Metabolism measured severe dehydration as losing more than 2% of a runner’s bodyweight. The study found that those running less than 60 minutes at a time could get by without liquids and not become severely dehydrated. Run longer than 60 minutes, and subjects required between “0-1.4L/hour.” That’s a very wide range.

And, although subjects running less than 60 minutes didn’t need fluids to stay alive, they more than likely would have felt better hydrating a bit on the run, especially in warm temperatures and/or if they have a high sweat rate and/or they hadn’t been pre-hydrating.

How much you drink on a run is a personal matter that takes trial and error, though it’s best to take small sips while running rather than big gulps. Large amounts of water at one time on a run can create side stiches and sloshy bellies.

And the most straightforward way to know if you need to drink is: Are you thirsty? If so, take a sip. But for run/run-walks under or well-under an hour, if you’re thirsty and don’t take a sip, you’ll likely be just fine until you get home.

What You Drink on a Run Depends  

Your options for what to drink on a run include plain water, electrolyte replacement (just sodium and minerals, like nuun hydration tablets), sports drink (electrolytes plus carbohydrates, and usually minerals and nutrients, like Skratch Labs Hydration Mix), energy drink (sports drink with stimulants like caffeine or guarana, like Gatorade Fast Twitch). What works for you is, again, personal preference and will require trial and error.

Some runners experience stomach upset ingesting liquids that contain sugar while running. Others depend on liquids with sugars/carbohydrates during long runs and refer to their drinks as “liquid calories.” Some runners find enhanced performance ingesting caffeine before or during a run, some find caffeine can send them searching for a toilet. Water is the safest bet.

As NPR reported, it is possible to hydrate too much with just plain water. Runners have died or become severely ill with hyponatremia, which happens when the concentration of sodium in your blood becomes too low. By drinking too much water, you basically flush out your own system too much.

But for short runs - outings of less than an hour - drinking plain water or one of the other options mentioned in small sips should be sufficient. If it makes you feel bad, try something else.

Carrying Liquids on the Run is Easier Than Ever

There are a multitude of ways to carry liquids comfortably on a run. For runs shorter than an hour, your best options include:

Handheld water bottles or soft flasks.

Holding a hard-sided bottle between 4 ounces and 20 ounces in hand has been made more comfortable over the years by brands like Amphipod, Nathan Sports, and Ultimate Direction. Bottles have become ergonomic and pair with comfortable hand straps. That said, hard-sided water bottles can be heavy when full, so if you use one, switch hands occasionally to not cause muscle imbalances and pains. Handheld soft flasks from similar companies and more (like Salomon) are nice because they “deflate” as you drink from them. Once empty, you can even shove the empty flask into a pocket or waistband and run free of anything in hand.

Waistbelts with small bottles or soft flasks.

Waistbelts that carry one or more small bottles, or that can fit a soft flask horizontally, can be nice in that they allow you to run hands-free. Finding one that doesn’t bounce too much while running on flats or downhill (they all tend to stay put on uphills) requires trying them on and jumping around a bit. There are a lot of good options with stretchy, comfortable straps and breathable materials.

Hydration vest with soft flasks.

Sometime in the last 10 years, hydration “vests” - over-the-shoulder packs with wide, vest-like shoulder straps with large pockets on each side - started taking over the trail running gear shelves. The benefits to packs like this over traditional “CamelBak”-like packs is that by holding two soft flasks, one in each chest pocket, the water is more evenly distributed than it is in one large hydration bladder on your back.

Also, hydration vests allow you to store gear needed in the backside pockets, like a layer of clothing which doesn’t weigh as much as water, and then the liquid on your frontside. That system has become popular with ultrarunners for comfort and convenience reasons - it’s also easier to refill flasks at aid stations than it is to refill hydration bladders.

I don’t list hydration bladders on this list because they carry between 1.5 liters and 4 liters of liquids, and liquid is heavy. Unless you sweat buckets and run in excessive heat, you likely don’t need to carry that much water. If either or both of those things is true, then a bladder makes sense to carry. Make sure the pack you’re wearing to carry the bladder fits you well, doesn’t rub, and doesn’t bounce or slosh around too much.      

Also note: if you do a race of any sort, know that there will likely be water stations every mile or so, making it virtually unnecessary to carry any (heavy) water yourself.

Post-Run Hydration is Also Important

After your run, properly hydrating - with electrolytes and maybe carbohydrates - can help you feel worlds better for the rest of the day than if you don’t. Experiment with what kind of post-run hydration makes you feel the best and stick to it.

So be it if that hydration is a frothy IPA. 

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