How to Hydrate for Gravel Cycling Races

I’ve been in this movie before.

In the guts of Kanza, it took 100 miles. In Belgian Waffle Ride, I managed to delay it until mile 120. In the first stage of the Joe Martin Stage race, it emerged at mile 90.

The ‘it’ manifested, in the same way, each time. I couldn’t eat food, even if I forced the food into my mouth, chewed, and tried to swallow. The moment I forced the food down my throat, a buried, unseen control center in my body issued a command against my will and reversed my conscious orders, sending the food back.

The ‘it’ also manifested consistently in the form of cramps. At Kanza, everything cramped, and I mean everything – my eyebrows, facial muscles, legs, arms, and back. At the Belgian waffle ride, my calves twitched so severely I had to get out of the saddle to keep pedaling. In Joe Martin, my body prevented me from getting in the drops because the closed hip angle overwhelmed my sartorius muscle.

The ‘it’ here is dehydration, and if you’re a gravel racer, managing it is just as crucial to your performance as your fitness or tire choice.

I’ve been racing bikes for nine years and descended from a tribe of humans in the Norwegian fjords that thought 50 F constituted a warm summer day. Hence, it’s remarkable I’ve made it this far without investigating the science of endurance hydration and developed a strategy to improve my performance.

But I have now, and it’s changed everything. If you want to cheat yourself of the background of hydration, skip to the bottom of the article. For the rest of you, hang onto your butts because we’re going to do a quick survey course in endurance hydration.

Here's the deal - humans are physically useless out in the wild, except for one thing - we're excellent at dissipating heat.

The reason we’re so good is unlike other mammals. We have abundant sweat glands. We have two types, but only one is worth mentioning: Eccrine glands.

Eccrine glands are super tiny, and we have thousands of them all over our bodies. Thanks to eccrine glands, we can secrete sweat went we generate a lot of heat which evaporates off of our skin and cools us. Other animals can’t do that, so they have to stop moving. Thus, persistence hunting was born – chasing after animals until they overheat and then killing them as they sit there helplessly unable to move.

Anyway, regulating heat is critical to endurance performance because one of the primary systems that power endurance – the cardiovascular system – actually performs two jobs – delivering energy to the working muscles and regulating our temperature.

As you can imagine, those two jobs aren’t easy, and the body prioritizes one function over the other. Can you guess what that is?

It’s heat regulation. Your body doesn’t care if you can still ride at threshold after five hours in 100 F temperatures. Its first job is to make sure your internal temperature remains at the proper temperature for cellular activity because if things get too steamy inside, cellular processes become impossible, and, beyond a certain point, you’ll die.

The primary mechanism your body has to dissipate heat is through sweat, and your ability to sweat depends primarily on your blood plasma.

Your blood plasma? Yes, your blood plasma.

Suppose you’ve read Tyler Hamilton’s book on doping. In that case, you’ll remember him remarking about his performance directly after taking out his blood so he could put it in later during the Tour de France and how dramatically his performance dropped after the blood draw. He concluded that “Your performance is all in your blood.”

He’s not wrong. Except, he talked about hematocrit levels, while we’re talking about blood plasma levels, but the principle remains the same. If your blood plasma volume drops, your blood gets thicker, and it becomes even more difficult to transport oxygen to your working muscles and dissipate heat. The result is that your performance necessarily drops as your body prioritizes heat regulation over-delivering oxygen to working muscles.

So how do you maintain your blood plasma volume during training and racing?

The first hard reality is that you can’t. Once you start riding, you’re in a losing sweat game, which brings me to my first significant point –

Always start exercise 100% hydrated.

Scientists have done studies on this and estimate roughly 30% of athletes start their workouts in a dehydrated state. That’s appalling. Think of all the time and effort into training, hoping that it’ll produce positive fitness progression but beginning every workout half in the can because you’re dehydrated. The dehydration would limit your potential progression because you’d perform each workout less well than if you began the exercise adequately hydrated.

OK, sure, once you begin training, you can never wholly replace your sweat losses. However, you can mitigate the loss. While this sounds insignificant, remember, once your blood plasma volume drops to a certain level, your performance rapidly tanks, so any strategy that delays that or avoids that point will lead to dramatic improvements in performance.

The key to maintaining blood plasma levels is sodium. Sodium is one type of electrolyte. Electrolytes are a widespread but poorly understood buzzword in sports drinks. Potassium, calcium, and magnesium are also essential electrolytes. Still, the most crucial electrolyte for sweating is sodium because it predominates in the extracellular fluid, the fluid between cells.

We need to maintain a stable sodium level in the extracellular fluids for nerve conduction, nutrient absorption, muscle contraction, and fluid balance in the body. Sodium allows you to absorb and maintain the fluid you take in to keep blood plasma levels high, decreasing the cardiovascular system’s strain as it delivers oxygen to working muscles and dissipates heat.

'Huh? Why can't I drink water? That's always worked for me."

Well, you’re either lucky, unaware of how much faster you could be if you took in sodium, or aren’t competing in long, challenging endurance events, but you are bringing up a good point – why can’t you drink water when you feel like it?

The problem with just drinking water during hot, long-endurance events is that you’re likely making your hydration status worse, not better. While the amount of sodium each of us expells when we sweat varies genetically, we all excrete some sodium. Sodium isn’t something our body can make. It’s something we have to ingest. So if you’re training hard for a long time in a hot environment, you’re depleting your sodium stores and disrupting the delicate electrolyte balance your body requires for cellular function. If all you take in is water, you’re diluting your blood plasma even more and run the risk of a condition called hyponatremia, or low blood sodium levels. When blood sodium levels get too low, the body fights back by forcing fluid out of the cells into the blood, making people swell up.

That would be funny, except that this also happens in your skull, which can cause your brain to swell up and, in some cases, leads to death. I’m not joking. No, it happens all the time.

So yeah, water isn’t enough. You need sodium. But how much sodium? How much water? Should you take sodium through fluid, or should you have electrolyte tablets?

Great questions. Unfortunately, there aren’t universal answers. Like so many aspects of endurance sport, there are general principles to follow but determining the optimal formula for you to maximize performance requires experimentation. Let’s start with the general principles.

1. Separate fueling and hydration

Eat your calories and drink your hydration. The reason for this is when you’re consuming your energy, that alters the tonicity of the fluid your drink and doesn’t create enough of a gradient from your cells to your blood required to maintain your blood plasma levels. 

2. Determine your sweat rate

So, ideally, you’ll want your drink to contain a particular concentration of sodium specific to your sweat rate to mitigate the drop in your blood plasma. That begs the question of what the hell your sweat rate is. You have three options here:

  • You can go into a lab and take a test.
  • You can administer your test.
  • You can ballpark your sweat rate.  

For the sake of simplicity, let’s ballpark it. Answer this: after you ride hard in hot conditions, what do your bibs look like? Do they look like you haven’t even ridden hard, or do they look like you’ve soaked them in a vat of salt? 

If they’re pristine, you probably don’t excrete that much sodium through sweat. If it’s the latter, you’re probably an oversized sweater and excrete lots of sodium.  

OK, here’s what you do:

Clean bibs? Put a 500 mg sodium tablet in your water bottle.

Kinda salty? Put a 750-1000 mg sodium tablet in your water bottle.

Really salty? Put a 1500 mg sodium tablet in your water bottle.

Drink a bottle like that every hour you’re riding in hot conditions.  

How do you know if it’s working? Two things:  

  1. You can continue to eat.
  2. You don’t crack and have to reduce your work rate dramatically.

How about if you overdid it? Acute signs of too much are bloating, fluid sloshing in the stomach, needing to pee frequently, and struggling to force drinks down. 

How do you know if you underdid it? Acute signs of not drinking enough are thirst, lightheadedness, higher heart rate than power output or pace, and lethargy. 

3. Be flexible in your framework

In application, what I just recommended is straightforward, but you need to experiment to refine the ideal hydration protocol. Suppose you take away nothing else from this sprawling article. In that case, you should use this newfound knowledge of endurance hydration to develop a flexible framework that you can adjust to different conditions.


4. Rehydration

I wish I could cut off the article here, but I’d be remiss if I didn’t discuss rehydration or the importance of hydrating after exercise. 

Whenever you smash yourself hard in hot conditions, it takes a toll on your body. How you replace what you’ve lost in fluids after training/racing, just like refueling with carbohydrates or sleeping, plays a crucial role in how fast you recover. Rehydration demand depends on two things:

  1. Level of dehydration at the finish
  2. How soon afterward you want to be 💯

If sweat losses are low and you don’t need to perform again soon, drinking and eating to thirst is enough. 

When sweat losses are high, and you need to perform again soon, you need a proactive approach. 

If you need to perform again soon, you’ll need to drink about one and a half times or more of the fluid you lost and plenty of sodium also. 

You have to drink so much more than you sweat out because you end up urinating out a good part of what you drink. Once again, our superhero electrolyte sodium helps. Adding sodium prevents your blood sodium level from dropping too low. Without it, your kidney kicks in and starts making you pee out what you tried to replace.

5. Curb your intensity

With all this background on hydration for gravel racing, you might think that all you have to do to keep going hard for these events is to figure out your hydration strategy, and you can go all out all day. Sadly, that’s not true.

While hydration is undoubtedly a key limiter in sustainable biking intensity, it’s not the only factor at play. Your fitness, ability to process carbohydrates, body composition, fatigue state, mental resilience, and flexibility also matter. I’m not going to dive into each here, but suffice to say you can’t out-hydrate your intensity. In other words, just because you’ve figured out how to hydrate doesn’t mean you’re exempt from pacing yourself in long gravel races.

OK, let’s wrap this up:

Hydration matters to performance because your cardiovascular system has two jobs – delivering oxygen to working muscles and regulating heat. If you get too hot, performance drops. Humans rely on sweating to regulate heat, and your blood plasma levels determine your ability to sweat. To maintain your blood plasma levels, you need to replace fluid and sodium losses in your sweat. The rate at which you sweat is genetically determined, but you can ballpark your sweat rate based on the conditions of your bibs in hot conditions. Adding sodium to your water bottles will help you maintain blood plasma volume and allow you to keep riding harder longer. How much sodium you need in your water bottle varies based upon your genetics, heat, and the duration of the event. Lastly, no matter how much you nail your hydration, you can’t outdrink dumb pacing.


If you skipped down to this portion of the article, here’s all you need to know:

1. Determine your sweat rate.
2. Pre hydrate days before with sodium.
3. Pre hydrate before the race with sodium.
4. Hydrate early and often with a sodium plan during the race.
5. Drink to hydrate, eat to fuel.
6. Keep intensity measured.


I totally forgot to mention cramping.

Here’s the deal, no one definitively knows why we cramp, but there are two competing schools of thought on the matter.

  1. Dehydration/electrolyte theory – If you lose a lot of water/sodium through sweating and don’t replace it fluid shift occurs and triggers cramps. 

  2. Neuromuscular theory – Muscles cramp when overworked and fatigued causing them to fire strangely. 

Which one is right? Well, both are.  Like so many things, the truth is somewhere in the middle.

Bottom line, no amount of sodium or pickle juice is going to preclude cramping in a long, hot ride if you’re not fit enough to handle the stress. Conversely, no amount of fitness will stop you from cramping in a long, hot ride if you don’t hydrate properly.

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