90% of Your Runs Don’t Need Electrolytes—Here’s When They Actually Matter
Estimated read time: 3.36 minutes (a lot less than it takes to read every conflicting electrolyte opinion on Reddit and still feel confused 🤔)
Hey Performance Nerds! Jonah here. 🤓
90% of your runs don't need electrolytes — even in the heat.
I said it last week, but it’s worth repeating, my only loyalty is to good science and helping runners train smarter.
Most runners use them out of habit, not science.
Sodium only matters when your fluid replacement catches up to your sweat losses, not every time you lace up.
Here's what you'll learn today:
The exact moment electrolytes start mattering (it's not "when you sweat")
How to match sodium to your actual fluid replacement
Simple decision framework: when to skip, when to sip
(Augie drinks from mud puddles with zero electrolytes and still outruns me to the mailbox. Clearly, duration matters more than drama.)
🗽 Good Luck, NYC — You’ve Got This
To everyone racing New York this weekend, good luck, have fun, and soak it all in.
I’ll be around the city and on course, if you see me, stop and say hi.
If there’s anything I can do to help or support you, please let me know.
🧬 Performance Sponsors:
🚀 Train Harder. Recover Smarter.
SiS—the same science-backed fuel trusted by Olympic marathoners—is now sponsoring Marathon Science.
From gels to recovery tools, every product is backed by real performance data and built for serious athletes like you.
🚀 Power Your Pace with Stryd
Stryd — the running power meter trusted by serious athletes — is now an official performance sponsor of Marathon Science, delivering real-time pacing precision so you can train smarter and race faster.
💡 See this week’s full Stryd training tip at the end of this newsletter.
🗺️ When Electrolytes Actually Matter
Here's the truth most supplement brands won't tell you: It's the relationship between sodium and fluid that matters, not how much sodium you lose
Your blood sodium tends to rise during exercise.
That's right—rise, not fall.
Unless you're drinking enough to replace most of your sweat, your body is naturally concentrating sodium in your blood when you run.
Sodium as the traffic light that tells water where to go, not the fuel itself.
Electrolytes become relevant when fluid replacement hits 50-70% of losses. That usually happens around 2-3 hours of running, or earlier in hot conditions when you're drinking more aggressively.
The Decision Table
Condition | Do You Need Electrolytes? | Why | Target |
< 2 hours | No for most runners | Small losses; plasma sodium rises naturally | Plain water + normal meals |
2-3 hours (temperate) | Maybe | Moderate fluid intake starts diluting plasma | 300-600 mg Na/hr if drinking heavily |
> 3 hours, marathons, ultras | Yes | High fluid turnover requires balance | 300-600 mg Na/hr (↑ in heat) |
Hot/humid at any duration | Moves you up a row | Higher sweat rate = more drinking | Start 300-600 mg/hr, test in training |
The principle: Match sodium to fluid replacement, not to your sweat test results.
Precision testing is optional, but helpful if you’re an exceptionally heavy sweater, racing in hot conditions, or just know hydration feels tricky for you.
Unlike fueling, sweat losses vary widely between athletes, so testing can give you a clearer baseline to personalize from.
Hyper-salty mixes can hurt palatability and cause gut issues anyway.
Keep solutions moderate and drink to thirst.
🔧 The Protocol: Before, During, After
Before Your Run
Skip the pre-run sodium for most training.
The exception: If you routinely start underhydrated or it's a hot race, use 275-420 mg sodium per 100 mL of fluid in the 4 hours pre-run.
This helps your body retain more fluid. Capsules work if salty drinks taste bad.
Otherwise? Save your money.
During Your Run (This Is Where It Matters)
Under 2 hours: No sodium needed for most runners.
2-3 hours or heat/high sweat: Consider 300-600 mg sodium per hour via drinks, gels, chews, or capsules. Drink to thirst, not to a schedule.
3+ hours or ultras: Same range (300-600 mg/hr). Personalize to your gut tolerance and conditions.
Important: Sodium won't "fix cramps" by itself. Its job here is fluid balance, not magic.
After Your Run
Salty foods or a normal meal usually cover it.
Your kidneys conserve sodium fast after exercise.
Exceptions:
Another hard session soon? If you finished very depleted and have another workout the same day or next morning, add sodium to your rehydration drink.
No salty food for a while? If you won’t be eating or drinking anything salty for a few hours, electrolytes can bridge the gap until your next meal.
Otherwise? Food beats special drinks.
⚡ Myth-Busting: Rapid Fire
"Should I replace 100% of sweat sodium?"
→ No. You'll likely overshoot plasma sodium if fluid replacement is low. Most runners only replace 50-70% of fluid losses anyway.
"Does sodium improve performance?"
→ Only if it helps you drink appropriately and keep balance. It's not a performance enhancer, it's a fluid tool.
"Electrolytes stop cramps?"
→ Cramping is multifactorial. Sodium helps with fluid balance, but it won't fix fatigue, pace, or neuromuscular changes that lead to cramps.
🎯 Practical Summary: When To Actually Use Electrolytes
Key takeaways:
Under 2 hours: You probably don’t need it. Your plasma sodium rises naturally.
2-3 hours or heat: Consider 300-600 mg/hr if you're drinking a lot.
Beyond 3 hours: Use it deliberately. Test your protocol in training.
The big picture: Electrolytes = timing tool, not a morning routine.
Bottom line: The question isn't how salty your sweat is. It's how much water you're replacing.
Match your sodium to your bottles, not your sweat test results.
💬 One last thing before you go.
If you’re rethinking your fueling plan or long-run strategy, hit reply. I read every message and I’m here to help.
What’s your current plan for runs over 2 hours or NYC this weekend? I’d love to hear it.
— Jonah
Are You a True Running Nerd? Prove it.. 🧐
Welcome to the prove you’re a nerd section. Each week, I ask a question about a common running science myth.
Answer correctly, and you’ll be entered into a weekly raffle to win a package of Jonah’s favorite supplements.
A 2025 study found post-run heat therapy (like hot-water immersion) may beat cold for long-term muscle repair and adaptation — not just short-term soreness. What’s the key physiological reason why?
- A. Heat boosts muscle blood flow, mitochondrial signaling, and satellite cell activity — accelerating repair and adaptation 🔥💪
- B. Cold reduces inflammation and swelling, helping muscles “heal” faster by limiting soreness ❄️🧊
- C. Cold constricts blood vessels to trap nutrients in damaged tissue for repair 🚫💉
- D. Heat causes mild dehydration, concentrating growth hormones for faster recovery 💧📈
Last Week’s Results: The Heat Is Learned, Not Earned 🔥
Turns out, you can’t fake heat fitness. Most of you got this one right: your body needs time to remodel, not just sweat through a few warm runs.
The correct answer?
C. 10–14 days of structured heat sessions 🔥✅
Research shows it takes roughly two weeks of consistent, controlled exposure for your body to adapt: plasma volume expands, sweat rate improves, and your heart rate normalizes at the same workload.
Those first few days? You’re just overheating and suffering. The second week is when the real physiological changes click in.
Here’s how the votes shook out:
⬜️ A. 2–3 days — the body adjusts fast 🌤️ – 13
🟨 B. 5–7 days of consistent exposure 🌡️ – 55
🟩 C. 10–14 days of structured heat sessions 🔥✅ – 177
⬜️ D. A full month of daily runs in heat 🗓️ – 17
Bottom line?
Give your body 10–14 days to truly acclimate — not just tolerate — the heat. The sweat, plasma, and pacing gains will follow. 🌡️💪
🏃♂️ Stryd Training Tip — Why Wind and Hills Secretly Cost You More Energy (and How Stryd Fixes It)
Think your pace tells the whole story? It doesn’t.
When you hit a hill or a headwind, your speed might stay the same, but your oxygen use spikes. That’s because your body has to recruit more muscle fibers just to produce the same forward force.
More fibers firing = more energy cost. Same pace, higher effort.
That’s where Stryd Power comes in.
By measuring your running power output, Stryd accounts for terrain and wind in real time, so you can keep effort consistent even when conditions change.
Here’s why it matters:
✅ Terrain-proof pacing: Hills and wind demand more force, but power-based pacing keeps your workload steady.
✅ Smarter energy use: Stryd shows when you’re overspending energy early so you can save glycogen for the finish.
✅ Objective feedback: Track how external conditions affect your efficiency, and adapt training to handle those stressors better.
💡 Bottom line: Wind and hills make your body work harder than pace alone can show—but with Stryd, you can see the true effort behind every stride and train smarter for real-world race conditions.
Don’t forget: You + Science = AWESOMENESS 😎
Yours in science,
Jonah
P.S. - We have a crew of 20,341+ nerds here who are running FAST using science.
Did you need running science advice or tips? 🏃♀️💨🧪
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