What Every Runner Should Know About Electrolytes

Mile seven. Your calf seizes up without warning — not a twinge, not a warning shot, just a sudden, violent knot that stops you cold on the side of the trail. You've had plenty of water. You stretched before the run. And yet here you are, standing with one foot on a rock, trying to force your leg to unclench while other runners pass you. Dehydration probably isn't the full story. The missing piece is almost always electrolytes — and more specifically, the ones you aren't replacing.

Why Runners Lose More Than Other People

Electrolytes are minerals that carry an electrical charge in your body's fluids — sodium, potassium, magnesium, calcium, chloride, and a few others. They regulate everything from nerve signals to muscle contractions to how much fluid your cells hold. You lose them through sweat. And runners sweat a lot more than most people realize.

A moderately active runner in mild conditions might lose around 0.8 liters of sweat per hour. Push that into summer heat or a hard tempo effort, and you're looking at 1.5 to 2 liters per hour. With each liter of sweat, you lose roughly 400 to 1,000mg of sodium, depending on your sweat composition — which is why blanket hydration advice rarely fits everyone. Some runners are "salty sweaters" who can taste the salt on their upper lip after ten minutes. Others lose less sodium per hour but still accumulate real deficits on a long run.

Potassium and magnesium also leave with your sweat. Most runners pay almost no attention to either.

The Sodium-Potassium Pump (and Why Your Muscles Care)

Every muscle contraction in your legs depends on something called the sodium-potassium pump — a mechanism inside your muscle cells that moves sodium out and potassium in to reset the cell for the next contraction. When you're running, this process is firing thousands of times per minute across hundreds of thousands of muscle fibers. It requires both minerals to work properly. Drop either one too low and the pump starts to stall. Contractions become irregular. Muscles fatigue faster than they should. In a worst-case scenario, you get the kind of cramp that stops a race.

Most runners treat electrolyte replacement like it's a sodium problem. Grab a Gatorade. Take a salt tab. Call it done. That handles part of the equation — but sodium without adequate potassium is like trying to run on one shoe. The pump needs both sides of the exchange.

Where the Cramp Story Gets More Complicated

The research on exercise-induced cramping has shifted over the past decade. The old theory — that cramps are purely a dehydration problem — has given way to a more specific understanding: electrolyte imbalances, particularly low potassium and low magnesium, are the more likely driver for runners who are already drinking plenty of fluid.

Magnesium regulates muscle relaxation specifically. Without enough of it, the contraction phase of a muscle cycle can't release properly — the muscle fires but can't fully unwind between contractions. Hold that pattern for seven miles and you have a calf cramp that stops a run cold.

The common mistake afterward is reaching for water instead of electrolytes. Drinking more plain water when you're already depleted dilutes what's left in your system, which can make things worse.

When to Take Electrolytes as a Runner

Timing matters. For runs under 45 minutes in moderate weather, plain water is probably sufficient. For anything over 45 to 60 minutes — especially in heat above 75°F — you want electrolytes during the run, not just after. By the time you feel thirsty or sluggish, you're already behind. A run that starts at 6 a.m. in May feels very different by mile nine at 8:30 a.m. when the temperature has climbed 15 degrees and your shirt is soaked.

Post-run replacement matters just as much for runners in back-to-back training days. What you replenish in the first 30 minutes after a long run affects how your legs feel the next morning. Skipping that window because you're tired and want a shower is one of the more common training mistakes that accumulates quietly over a season.

Early-morning runners should also consider a quick electrolyte dose 20 to 30 minutes before heading out. You wake up at least mildly dehydrated after eight hours without fluids — starting the run ahead of that deficit is easier than chasing it.

The Sugar Problem in Most Sports Drinks

A standard 20-ounce bottle of Gatorade contains around 36 grams of sugar. For long endurance events where you need fast fuel, that can make sense. For most training runs, it introduces a different problem. High-sugar drinks can cause GI distress mid-effort, particularly in runners sensitive to fructose or those running at higher intensities. The gut is already shuttling blood to working muscles — asking it to process 36 grams of sugar simultaneously doesn't always go well.

The nausea or side-stitch that hits some runners after aid station drinks isn't always nerves or pace. It's often the sugar content of whatever was in the cup.

Reading an Electrolyte Label as a Runner

When you're evaluating a product, three numbers matter most: sodium, potassium, and magnesium. Look for at least 400mg of sodium per serving and at least 600mg of potassium. Most commercial sports drinks fall short on potassium — Gatorade Endurance, for example, has about 200mg. Salt tabs give you sodium only. Neither addresses the full equation.

One more thing to check: the form of each mineral. Potassium chloride is the cheapest and most common form. Potassium citrate is more bioavailable — your gut absorbs more of it per milligram. Same story with magnesium: magnesium citrate outperforms magnesium oxide, which is common in budget supplements. Citrate forms cost more to source, which is why they're less common on labels. But when you're asking your body to perform at mile seven, the form of the mineral matters as much as the count.

Most runners are still hydrating with whatever ended up in the aid station bag — a packet handed over mid-stride, dumped into a half-crushed cup. That's fine for surviving a race. It's not a hydration strategy. If you're putting serious miles on your legs, the formulation of what you're drinking deserves the same attention you give your shoe drop or your training plan.

What to Actually Look for in a Running Electrolyte

Start with those three numbers: sodium, potassium, magnesium. Then check the forms. Citrate forms for both potassium and magnesium will serve you better on a long run than their chloride counterparts — more of what's on the label actually makes it into circulation.

A few options worth knowing:

LMNT runs high on sodium (1,000mg per serving) with lower potassium (200mg) — a good fit for heavy sweaters in hot climates who lose a lot of sodium per hour, but it undershoots the potassium side of the sodium-potassium pump equation.

Nuun comes in tablet form and is convenient for travel, but the overall mineral count is lower — around 300mg sodium and 150mg potassium per tablet — which works for shorter efforts but may not cover a half-marathon training run in July.

Precision Hydration offers tiered products calibrated to sweat rate, which is a smart approach for runners who know whether they're light or heavy sweaters.

VitaWild is built around a different priority: hitting the potassium side hard while staying completely sugar-free. Each stick pack delivers 450mg sodium, 800mg potassium as potassium citrate — one of the higher potassium counts in any zero-sugar electrolyte formula on the market — and 75mg magnesium as magnesium citrate. The citrate forms on both minerals mean better absorption, not just better numbers on a label. There's also a B-complex (B3, B6, B12, B5) that supports energy metabolism during the run, which is a practical addition for runners who feel that mid-run fog hit around mile eight.

Zero added sugar, no artificial colors or flavors, stick packs that fit in a vest pocket. For runners who want a complete electrolyte profile with vitamins and no GI-aggravating sweeteners, it's worth carrying.

Running performance is 90% showing up and putting in the work. But within the 10% you can actually control, electrolyte replacement is one of the few levers with an immediate, measurable effect. Swap the sugar-heavy sports drink for something with real potassium and citrate-form magnesium, time it right around your longer runs, and see if mile seven starts feeling like mile four again. The test doesn't take long to run.

Related reading: What Are Electrolytes? · Why Your Body Can't Absorb Electrolyte Supplements · Pickleball Hydration: What to Drink Before, During, and After