TLDR: When to Take Electrolytes whilst Running? Electrolytes aren’t a cure all for cramp. Most runs don’t require them, but for hot, long, or ultra-endurance events, they can make a real difference. The science shows that when you run shorter or moderate sessions you usually don’t need to replace sodium unless you’re sweating heavily and drinking lots. The exceptions are really long days out, especially if its warm, when sweat losses stack up and fluid intake is high. That’s when replacing sodium (salt) becomes important.
f you’ve been on any running forum, you’ll have seen debates about salt tablets, electrolyte drinks, and “avoiding cramp.” It can feel like every brand is screaming that you must take their tabs or powders or risk collapsing by mile 10. The truth is a little more nuanced than that. Electrolytes, mainly sodium, do matter, but when they matter is the key question.
Electrolytes are minerals in your body fluids that carry an electric charge. The big ones you’ll hear about in sports drinks are sodium, potassium, calcium, and magnesium.
So while “electrolytes” sounds plural, in endurance running it’s really sodium that you need to think about. The others tag along in sports drinks more for balance and marketing than being strictly necessity.
A 2022 modelling study led by Alan McCubbin looked at how much sodium athletes actually need across different sports. Here’s what the data showed:
So, the takeaway? Sodium is rarely a limiting factor in everyday runs or even most marathons. But in ultra-distance events, it becomes part of the equation.
The only way to know your exact sodium needs is through a sweat sodium test. These are usually done in a sports lab or by some specialist companies. A small patch or sensor is placed on your skin (often the forearm), your sweat is stimulated or collected during exercise, and then analysed for sodium concentration.
This test tells you whether you’re a “salty sweater” (losing lots of sodium per litre of sweat) or on the lower end.
Sweat sodium testing is more of a nice-to-have than a need-to-have. McCubbin’s modelling study shows that most athletes don’t need precision testing unless they’re doing very long ultras with high sweat rates and replacing a large proportion of fluid losses. For most runners, you can get by with estimated ranges and a bit of trial and error in training.
With that said, here are some practical sodium targets to guide you:
“If I don’t take electrolytes, I’ll cramp.”
Cramp is complicated. Research hasn’t shown sodium replacement prevents it. Fatigue, pacing, and conditioning are usually bigger drivers. If you do frequently cramp I’d still explore using electrolytes, but just know that other factors could likely be at play.
“I sweat loads, surely I need salt every run?”
Sweating heavily doesn’t always mean you need to replace sodium. Unless your run is long and you’re drinking a lot, your plasma sodium balance usually holds.
“I heard hyponatremia comes from not taking salt.”
Hyponatremia (dangerously low blood sodium) almost always comes from overdrinking water, not failing to take salt. Electrolytes can help balance things in ultras, but the bigger factor is fluid intake.
Paul is a sports nutrition consultant and educator with a PhD in Nutrition and Exercise Science. With over a decade of experience, Paul specialises in optimising performance and recovery for endurance athletes through evidence-based strategies. As a lecturer and researcher, Paul has published in peer-reviewed journals and worked with athletes, sports teams, and organisations to achieve peak performance.
