Electrolytes That Actually Matter for Endurance

Why endurance athletes keep blowing the electrolyte basics

Endurance sports look simple from the outside: run, ride, swim, repeat. But stay out there long enough and the chemistry experiment inside your body gets pretty wild.

Here’s the uncomfortable truth: most athletes either massively overdo electrolytes or barely use them at all. One group throws back salt tablets like candy. The other proudly drinks “only water” and wonders why they feel wrecked at the end of a hot race.

The reality sits in between. Your body isn’t trying to trick you, but it is trying to keep a very delicate balance of fluid and charged minerals so your nerves, muscles, and heart can keep working while you’re out there cooking at 140–180 beats per minute.

So instead of memorizing random “rules,” it helps to understand what each main electrolyte actually does when you’re pushing for hours.

Sodium: the one you really can’t ignore

If endurance sports had a main character in the electrolyte story, it would be sodium.

Sodium helps:

Maintain blood volume so your heart doesn’t have to work overtime
Support nerve signals so your muscles contract smoothly
Regulate fluid balance so water actually stays in your bloodstream and cells instead of rushing straight to your bladder

When you sweat, you lose sodium in much higher amounts than any other electrolyte. Some people lose a little. Some lose a lot. And some, like Mark, a 43-year-old age-group triathlete, only learn how salty they are when they finish long rides with white streaks on their jersey and a pounding headache.

Mark used to drink only water on his long brick sessions. Two hours in, he’d feel lightheaded, his hands a bit puffy, and his pace would fall apart. Classic signs that he wasn’t just dehydrated—he was diluting his blood sodium.

What happens when sodium gets too low during long efforts?

When blood sodium drops, you can see things like:

Headache, nausea, or feeling “off”
Swollen fingers or a puffy face
Confusion or difficulty focusing
A weird mix of fatigue and irritability

In severe cases, that can slide toward exercise-associated hyponatremia—dangerous, not just annoying. Organizations like the CDC and NIH have flagged this as a real risk in long events, especially when athletes drink large amounts of plain water for hours on end.

Where do you actually get sodium during training and racing?

You don’t need fancy products to get sodium, but you do need some plan. Endurance athletes usually rely on a mix of:

Electrolyte drink mixes or sports drinks
Gels that include sodium
Chews, capsules, or salt tablets
Regular foods with sodium (pretzels, broth, salted potatoes, etc.)

A marathoner like Jess, who finishes around 3:45, might get most of her sodium from a sports drink plus slightly salted breakfast and a gel every 30–40 minutes. An ultra runner out for 8–10 hours might lean more on salty foods and broth later in the day.

The key idea: if you’re sweating a lot for more than about 60–90 minutes, sodium becomes a performance tool, not just a trivia word on a label.

Potassium: the quiet partner that keeps muscles firing

Potassium doesn’t get the same hype as sodium, but your muscles care about it a lot.

Potassium helps:

Coordinate muscle contractions
Support normal heart rhythm
Work with sodium to keep fluid balanced inside and outside cells

You lose potassium in sweat, but usually less than sodium. Most well-fed athletes start workouts with decent potassium levels from everyday foods: potatoes, bananas, beans, yogurt, tomatoes, and leafy greens.

Take Sara, a 29-year-old marathoner who eats pretty clean but tends to under-eat overall during peak weeks. She’s not just low on calories; her overall mineral intake is borderline, too. On back-to-back long runs, she notices twitchy calves and an odd “heavy” feeling late in the run. Her bloodwork shows her potassium is low-normal. Once she bumps up whole foods rich in potassium and stops under-fueling, those weird muscle sensations ease up.

Do you need extra potassium during a race?

For most athletes:

Daily diet does the heavy lifting for potassium
During events, small amounts in sports drinks or gels are usually enough

You don’t want to go rogue with high-dose potassium supplements, especially if you have any kidney issues or take certain medications. High potassium can be dangerous. That’s why medical sites like Mayo Clinic and WebMD are pretty clear: more is not always better with this one.

Mayo Clinic potassium overview: https://www.mayoclinic.org/drugs-supplements-potassium/art-20368940
WebMD on potassium: https://www.webmd.com/diet/supplement-guide-potassium

For healthy endurance athletes, think of potassium as something to consistently support through food, then top off lightly with race nutrition—not something to megadose mid-race.

Magnesium: the “why am I cramping?” suspect (but not always the villain)

Magnesium has become the internet’s favorite answer to every endurance problem. Cramping? Must be magnesium. Poor sleep? Magnesium. Slow recovery? Definitely magnesium.

Reality check: magnesium does matter, but cramps are usually a messy mix of fatigue, pacing, conditioning, and overall electrolyte balance—not just one missing mineral.

Magnesium helps:

Over 300 enzyme reactions, including energy production
Muscle relaxation after contraction
Nerve signaling

Now meet Daniel, a 36-year-old cyclist who cramps in nearly every race longer than two hours. He’s convinced he has a magnesium issue and starts taking massive doses. The cramps don’t improve. What does change? His gut. Long rides now come with urgent bathroom stops.

He eventually works with a sports dietitian, who spots the real problem: he’s under-fueled, under-trained at race intensity, and takes in almost no sodium during events. Once he fixes pacing, carbs, and sodium, the cramps drop dramatically. Magnesium? Nice to have, but not the magic bullet.

Where magnesium fits for endurance athletes

Many people don’t hit recommended magnesium intake from food
Heavy sweaters and high-volume athletes may have higher needs
Good food sources: nuts, seeds, whole grains, beans, dark chocolate, leafy greens

Supplementing moderate amounts outside of training (for example, with dinner) can help if your diet is weak. But dumping high doses into your bottles or gels mid-session is a great way to get diarrhea, not a faster finish time.

If you suspect a real deficiency, that’s when a conversation with a healthcare professional and possibly bloodwork makes sense.

Calcium and chloride: the supporting cast you shouldn’t completely forget

Calcium gets all the glory for bone health, but it’s also involved in muscle contraction and nerve function. Most endurance athletes who eat dairy or fortified alternatives, plus some leafy greens, hit their needs just fine.

Chloride usually tags along with sodium as sodium chloride (plain old salt). It helps with fluid balance and stomach acid production. If you’re salting your food and using normal sports products, you’re almost certainly covering chloride without trying.

You rarely need to chase these two separately during a race. Instead, you make sure your overall diet isn’t a nutritional wasteland and let your sports nutrition products do their job.

So what does this look like in real training and racing?

Let’s get out of theory and into what this means on an actual long day.

The hot half marathon

Lena signs up for a half marathon that starts at 9 a.m. in early September. Forecast: 80°F and humid. She normally runs long with just water because “it’s only 2 hours.”

By mile 9, she’s slowing. Her head feels heavy, and she’s oddly bloated even though she’s thirsty. She’s grabbed water at every station but no electrolytes. Classic setup for low sodium relative to fluid intake.

Next race, she changes two things:

Drinks a sports drink with sodium at alternate aid stations
Takes gels that include sodium every 35–40 minutes

Same fitness, same course, same weather. She finishes stronger, no weird swelling, and recovers faster. The difference wasn’t magic training—it was smarter sodium and fluid balance.

The long bike ride

Now think about a 4–5 hour summer ride. You’re losing:

Fluid (sweat)
Sodium (a lot)
Smaller amounts of potassium, magnesium, and chloride

A decent on-bike strategy might combine:

A bottle with a proper electrolyte mix (not just flavored water)
Some solid or semi-solid foods that include salt (wraps, pretzels, salted bars)
Gels or chews with both carbs and sodium

Across those hours, you’re not just “staying hydrated.” You’re actively replacing the minerals that keep your heart, nerves, and muscles working under stress.

Are cramps always an electrolyte problem?

This is where things get messy. Everyone wants a simple answer: “I cramped, so I need more X.” Reality is more annoying.

Common contributors to cramps in endurance sports include:

Fatigue from going harder than you trained for
Poor pacing (overcooking the early miles)
Inadequate carb intake
Overall dehydration
Electrolyte imbalance (usually sodium, sometimes plus others)

Could low sodium or other electrolytes be part of the story? Absolutely. Are they the only story? Almost never.

If you’re constantly cramping:

Look at your training first: are you actually prepared for the pace and distance?
Then look at carbs and fluids: are you under-fueling?
Then fine-tune electrolytes: especially sodium, spread throughout the effort

And yes, sometimes, despite all of that, your individual physiology is just more cramp-prone. That’s where careful experimentation comes in.

How to actually dial in your electrolyte strategy

You don’t need lab testing to get started, but you do need to stop guessing blindly.

Start with these questions

Ask yourself:

How long am I usually out there? Under an hour, 1–3 hours, or all day?
How hot and humid are my typical conditions?
Do I finish long sessions with salt streaks on clothes or skin?
Do I often get headaches, nausea, or “brain fog” after long workouts?

If you’re doing short workouts in cool weather, water plus a decent diet may cover you. Once you’re going longer than 60–90 minutes, especially in heat, electrolytes move from “nice idea” to “performance gear.”

Use training, not race day, to experiment

You know the rule about not trying new shoes on race day? Same goes for new electrolyte products.

In long training sessions, test:

Different sports drinks or mixes: how does your gut handle them?
Gels or chews with varying sodium content
Timing: smaller, more frequent sips and bites usually beat big, random hits

Notice:

Energy levels late in the session
Any cramping, dizziness, or nausea
How thirsty you feel vs. how much you’re actually drinking

Fine-tune one variable at a time so you know what’s helping and what’s just marketing.

When should you be worried enough to talk to a doctor?

Most electrolyte tweaks are a matter of performance, not emergency medicine. But there are red flags where you stop guessing and get professional input.

Talk to a healthcare professional if you:

Have a history of kidney, heart, or endocrine issues
Take medications that affect fluid or electrolyte balance (like diuretics)
Feel confused, very disoriented, or severely nauseous during or after events
Have repeated episodes of extreme swelling, vomiting, or fainting in races

Resources worth bookmarking:

Mayo Clinic on dehydration and complications: https://www.mayoclinic.org/diseases-conditions/dehydration/symptoms-causes/syc-20354086
CDC on heat-related illness: https://www.cdc.gov/niosh/topics/heatstress/heatrelillness.html

Electrolytes are powerful, and yes, you can overdo them. If you’re piling on multiple high-sodium products, plus salty food, plus tablets, and you’re not a particularly salty sweater, that’s worth reviewing with a pro.

The bottom line: electrolytes as a performance tool, not a fad

Endurance racing is basically a long argument between your brain, your muscles, and your gut. Electrolytes don’t win that argument by themselves, but they give all three a fighting chance.

Sodium keeps your blood volume and nerve function in a range where you can keep pushing. Potassium and magnesium quietly support muscle and heart function. Calcium and chloride play their parts in the background. Ignore them and you might get away with it on cool, short days. Stretch the distance, crank up the heat, and the cracks start to show.

So the next time you plan a big race or a long training block, don’t just ask, “How many miles?” Ask:

What am I losing in my sweat, besides water?
How am I going to put it back—in a way my stomach can handle?

Get that right, and suddenly your “bad races” start looking a lot more like “bad plans” you can fix.

FAQ: Electrolytes and endurance sports

Do I need electrolytes for every workout?
Not really. For sessions under about 60 minutes in cool conditions, water is usually fine if your daily diet is solid. Once you’re out there longer than 60–90 minutes, especially in heat or humidity, adding electrolytes—mostly sodium—starts to matter more.

Are sports drinks enough, or do I need salt tablets too?
Sometimes sports drinks are enough, especially for shorter races or cooler days. If you’re a heavy or salty sweater, racing for several hours, or in very hot conditions, you may need extra sodium from gels, chews, or capsules on top of your drink. The only way to know is to test in training.

Can I just use table salt instead of fancy products?
You can absolutely use regular salt in food and homemade drink mixes. Many commercial products just package sodium (and sometimes carbs) in convenient, tested formulas. If you DIY, be careful with concentration so you don’t create a drink that’s too salty and hard on your stomach.

Do electrolytes prevent cramps completely?
No. They can help reduce the risk, especially when sodium loss is high, but cramps are usually driven by a mix of fatigue, pacing, training status, and overall hydration and fueling. Electrolytes are one tool, not a guarantee.

Is it possible to overdo electrolytes?
Yes. Mega-dosing sodium or potassium—especially if you have medical conditions or take certain medications—can be risky. More is not always better. Stick to reasonable amounts, spread them over time, and talk to a healthcare professional if you have any underlying health concerns.

Sweat, Salt, and Suffering: The Electrolytes Endurance Athletes Really Need