Hydration Tips for Ultra-Endurance Athletes

28 February 2026

When it comes to ultra-endurance events—whether it’s a grueling 100-mile trail race, an Ironman triathlon, or a multi-day cycling expedition—hydration isn’t just important, it’s everything.

Let’s be real: your body can go quite a while without food, but without water? You're toast in a matter of hours. So if you're pushing your physical and mental limits for hours (or even days), dialing in your hydration strategy could be the game-changer between finishing strong and hitting the dreaded DNF (Did Not Finish).

Let’s break it all down and see how to keep your body fueled, your mind sharp, and your legs moving strong through every mile.

Why Hydration Matters So Much in Ultra-Endurance Sports

Think of your body like a high-performance engine. Water is your coolant, your fuel mover, and your performance enhancer all rolled into one.

When you're sweating bucketloads during an ultra, you're not just losing water—you’re also losing essential electrolytes like sodium, potassium, and magnesium. These electrolytes are key for muscle function, nerve impulses, and overall energy transfer.

Let that balance get out of whack, and you’ll likely run into problems like:

- Muscle cramps
- Dizziness or confusion
- Fatigue
- GI issues
- Even more dangerous stuff like hyponatremia

So yeah... hydration isn’t just about avoiding thirst. It's about protecting your performance and your health.

Understand Your Sweat Rate

Here’s one of the most overlooked hydration tips: not everyone sweats the same. Some people drip like faucets while others stay relatively dry.

Why does that matter? Because your hydration plan needs to be customized to YOU, not based on someone else’s strategy.

How to Calculate Your Sweat Rate:

1. Weigh yourself before a training session (without clothes).
2. Do your workout for an hour (track how much you drink during).
3. Weigh yourself again after the workout (again, no clothes).
4. Subtract the post-workout weight from the pre-workout weight, and add the volume of fluids you drank.

That’s your sweat rate in liters/hour. Boom! Now you ACTUALLY know how much you’re losing.

Drink Early and Often—But Don’t Overdo It

It’s tempting to listen to your thirst as the only cue, but that’s like relying on your gas light to start looking for a gas station. It might be too late by then.

Pro-Tip:

Start drinking early in your race or training. Once you’re behind on fluids, it’s tough to catch up. But—and this is big—DO NOT overhydrate. Drinking too much water without proper electrolytes can lead to hyponatremia, a potentially life-threatening condition where sodium levels drop dangerously low.

So yeah, there’s a sweet spot. You want to aim for fluid replacement close to your sweat rate, not over it.

Electrolytes: Small But Mighty

If water is the gas, electrolytes are the oil. You need both to keep the engine from seizing.

When you're sweating like crazy, sodium is the main electrolyte you're losing. Some athletes can lose up to 1000mg of sodium per liter of sweat. That adds up fast over an ultra.

Your Electrolyte Strategy Should Include:

- Sodium: Helps retain fluids and prevents cramping.
- Potassium: Assists in muscle contraction and heart function.
- Magnesium and Calcium: Supports muscle relaxation and nerve impulses.

Most sports drinks don't have enough electrolytes for ultra-endurance needs. That’s where electrolyte capsules or higher-concentration drink mixes come into play.

Pro Tip:

Check your sweat for salt stains on your clothes or face. If you’re seeing salty streaks post-run, you’re likely a “salty sweater” and need higher sodium intake.

Drink to a Plan—Not Just to Thirst

While the whole “drink to thirst” concept works for short workouts, ultras are a different beast. You need a more proactive approach.

Here’s a Simple Race-Day Hydration Framework:

- Pre-Race: Drink 12–16 oz of water with electrolytes 1–2 hours before start time.
- During the Race: Drink 14–28 oz per hour, depending on your sweat rate, effort level, and weather. Include electrolytes every hour.
- Post-Race: Rehydrate with 150% of the fluid lost during the race, along with sodium-rich fluids or foods.

It’s less about guzzling gallons and more about sipping steadily, balancing fluid intake with electrolytes and carbs.

Temperature and Humidity: The Silent Game-Changers

Hot and humid conditions? You’re going to be sweating more, obvious right?

But it’s not just about more sweat—it’s also about how your body cools itself. High humidity slows down sweat evaporation, meaning your body retains more heat. In cold weather, it’s easier to forget to drink. Both scenarios mess with hydration.

Adjust Accordingly:

- Increase your fluid and electrolyte intake in hot conditions.
- Set reminders in colder weather to still drink fluids.
- In altitude? Sip more often. Dehydration kicks in faster up in the thinner air.

What About Caffeine and Alcohol?

You're probably not slamming beers mid-ultra (although some fun runs encourage it...), but the week leading up to the race? Watch your intake.

- Caffeine can be a performance enhancer and help with endurance, but it’s also a mild diuretic. Use it smart—usually in the early or middle stages when you need a focus boost.
- Alcohol dehydrates you. Avoid it during your taper and in the 24–48 hours before racing.

Practice Your Hydration Strategy in Training

This cannot be overstated: Nothing new on race day. That includes your hydration plan.

Try out different types of fluids, concentrations, and electrolyte supplements during your long training sessions to see what sits well in your stomach.

Everyone processes fluids differently. What works for your training buddy might make you spend a race on the side of the trail with gut issues.

Monitor for Dehydration and Overhydration Symptoms

Signs You Might Be Dehydrated:

- Dark yellow urine (lemonade color = you're good)
- Dry mouth or chapped lips
- Dizziness or lightheadedness
- Fast heart rate or feeling sluggish
- Cramps

Signs You Might Be Overhydrated:

- Swollen hands or feet
- Nausea or bloating
- Confusion or headaches
- Clear urine too frequently
- Weight gain during a race (yes, that’s water retention)

Keep tabs on yourself and make adjustments accordingly. Sometimes it helps to set hydration alarms on your watch or pre-plan intake per hour.

Real-World Hydration Examples from Elite Endurance Athletes

Let’s talk real-world strategy. Here’s how top ultra-athletes manage it:

- Courtney Dauwalter, one of the strongest ultrarunners out there, keeps it simple. She uses a steady drip of electrolyte drinks and gels, avoiding sudden spikes or stomach overload.
- Scott Jurek, an ultra-running legend, emphasized flexible hydration—adjusting intake based on terrain and intensity rather than by the clock.
- Ironman athletes often alternate between water and electrolyte drinks at aid stations, especially in the back half of races when fatigue and salt loss pile up.

The takeaway? Keep it simple, stay consistent, and always listen to your body.

Hydration Gear That Can Help

When you're running or biking for hours, carrying fluids can be a pain. But hydration packs and bottles have come a long way.

Recommended Gear:

- Handheld bottles: Good for shorter efforts or races with frequent aid stations.
- Hydration vests or packs: Great for long trail ultras—plenty of room for water, nutrition, and supplies.
- Soft flasks: Lightweight and stowable as you drink.
- Electrolyte tablets or capsules: Easy to carry and dose based on needs.

Choose gear that feels natural and make sure it doesn’t bounce around during movement. Hydration should never be a hassle.

A Few Final Hydration Hacks

Before we wrap up, here are some pro-level hydration hacks you might not have heard:

- Add a tiny pinch of salt to your water for a sodium boost if you’re out of tablets.
- Use flavor to your advantage. Mildly flavored drinks are easier to drink consistently than plain water.
- Set hourly reminders on your watch—it’s easy to lose track mid-race.
- Freeze your water bottles night before hot races—helps with core cooling early in the race.
- Weigh yourself pre and post long runs occasionally to stay aware of fluid loss.

Wrapping It Up

Hydration might not be the sexiest part of ultra-endurance sports, but it’s hands-down one of the most critical. Whether you're training for your first 50K or you’re a seasoned 100-miler, understanding and mastering your hydration strategy could be the difference between crushing it and crawling across the finish line (if you make it that far).

Get to know your body. Train your gut just like your legs. And most importantly, plan ahead with your hydration like your performance depends on it—because it does.