7 electrolyte mistakes endurance athletes make
Electrolytes are simple in theory and quietly botched in practice. Most endurance athletes either ignore them until they cramp or overcorrect and dump a scoop of everything into a bottle without knowing why. Both cost you.
Here are seven mistakes that show up again and again, and how to fix each one. Number two is the one almost everyone gets wrong.
1. Drinking plain water on long, sweaty efforts
Water replaces volume. It doesn't replace the sodium you lose in sweat, and on long or hot sessions that gap matters. Drink enough plain water while sweating heavily and you dilute your blood sodium further, which is the mechanism behind exercise-associated hyponatremia, a genuinely dangerous condition (ACSM position stand on fluid replacement).
The fix: on anything over about 60 to 90 minutes, or in the heat, put sodium in your bottle rather than relying on water alone.
2. Guessing your sodium instead of matching your sweat
This is the big one. Sweat sodium losses vary enormously between people, roughly from 200 to over 1,500 mg per litre of sweat, and the difference is mostly genetic (review of sweat electrolyte variability). A "salty sweater" who leaves white marks on their kit needs far more sodium than someone who doesn't, yet both usually copy the same generic dose off a label.
The fix: notice your own signs. Gritty, stinging eyes, white residue on your face and clothing, and cramp-prone muscles all point to high sodium losses. If that's you, dose higher and don't assume the standard scoop covers it. For a rough baseline, weigh yourself naked before and after a hard hour of training. Every kilogram lost is roughly a litre of sweat, and multiplying that by your estimated sweat sodium tells you how big a hole you're digging.
3. Chasing potassium and magnesium while under-dosing sodium
Marketing loves potassium and magnesium because they sound sophisticated. But you lose far more sodium than any other electrolyte in sweat, by an order of magnitude. Building a hydration plan around the minor players while skimping on the main one is backwards.
The fix: make sodium the anchor of your in-session electrolyte plan. Potassium, magnesium, and calcium matter for overall balance and recovery, but they don't replace sodium's job during exercise.
4. Only thinking about electrolytes during exercise
By the time you're mid-session, your hydration status is largely already set. Turn up sweating from a hot commute or a poor night's fluid intake and you're playing catch-up you can't win inside a race.
The fix: start topping up sodium and fluid in the hours before a long or hot session, rather than only during it. Pre-loading is standard practice for a reason. Our guide to pre-event hydration covers the timing.
5. Relying on sugary sports drinks for their electrolytes
Many mainstream sports drinks are built as carbohydrate drinks first, with electrolytes as a minor add-on. The sodium content is often too low for a heavy sweater, and you're taking on a lot of sugar to get it. That's fine if you specifically want the carbs. It's a poor way to hit a sodium target.
The fix: separate the two jobs. Use carbs for fuel when you need fuel, and use a dedicated electrolyte product for hydration so you can dose sodium properly without the sugar load.
6. Ignoring calcium entirely
Calcium gets left off the electrolyte list, yet it's the mineral that triggers every muscle contraction you make. You lose it in sweat too, in smaller amounts than sodium, and long-term shortfalls hit bone health rather than announcing themselves mid-run.
The fix: cover calcium through diet as standard, and treat it as part of a complete electrolyte formula rather than an afterthought. Our deeper look at calcium for athletes explains where it fits.
7. Treating one hydration plan as permanent
The dose that worked for a cool spring 10 km won't cover a humid summer Hyrox. Sweat rate rises with heat, intensity, and duration, so a fixed plan that ignores conditions will over- or under-shoot most of the time.
The fix: scale sodium and fluid to the day. Hotter, longer, and harder means more. Cooler and shorter means less. Weigh yourself before and after a few key sessions to learn your own sweat rate, then adjust rather than guessing.
The pattern behind all seven
Six of these mistakes come back to one habit: guessing instead of matching your own body. Sweat rate and sweat sodium are personal, and the athletes who get hydration right are the ones who pay attention to their own signals rather than copying a label. Get sodium right for you, cover the rest through a complete formula and your diet, and adjust for conditions. That's the whole game.
Frequently asked questions
How much sodium do endurance athletes need per hour?
It varies widely with sweat rate and sweat sodium concentration, but many athletes fall somewhere around 300 to 700 mg of sodium per hour on long efforts, and heavy or salty sweaters need more. Learn your own losses rather than relying on a single number.
Are electrolyte tablets enough on their own?
For hydration, yes, if they carry enough sodium for your sweat losses. They don't provide meaningful fuel, so on long efforts you may still need carbohydrate separately. Match the tool to the job.
Can you take too many electrolytes?
Yes. Overdoing sodium without enough fluid, or supplementing minerals you don't need, can cause GI upset and other issues. The aim is to match your losses, not to maximise intake.