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Electrolytes & Hydration: The Complete Guide

Hydration is more than water. Match your sodium to your sweat rate and the difference shows up in your last set, your last mile, and your cramp-free calves.

✍️ By Filip Mesec 🔄 Last updated 11 June 2026 ⏱ 7 min read ✅ Evidence-based
🔬 800–1500mg sodium lost per litre of sweat

What Are Electrolytes?

Electrolytes are minerals that carry an electrical charge when dissolved in body fluids — primarily sodium, potassium, magnesium, chloride and calcium. They regulate fluid balance, nerve signalling, and every muscle contraction you produce in training.

Sweat is not just water. Typical sweat contains roughly 800–1500mg of sodium per litre, and sweat rates during hard training commonly reach 1–2 litres per hour — more in heat. Sweat sodium concentration varies enormously between individuals (genetics, heat acclimation and diet all play a role), which is why a one-size-fits-all hydration plan fails so many people. If you finish sessions with white salt crust on your hat or shirt, you are likely on the high end.

Signs of electrolyte imbalance: Muscle cramps late in sessions, headaches after training, dizziness when standing, unusual fatigue despite drinking plenty, nausea during long efforts, and persistent thirst that water doesn't fix.

When is plain water enough?

  • Plain water is fine for most sessions under 60 minutes in moderate temperatures — your meals replace the sodium afterwards
  • Electrolytes start to matter beyond 60–90 minutes, in heat or humidity, or with back-to-back sessions
  • Water alone can backfire in long events: drinking litres of plain water while losing salty sweat dilutes blood sodium
  • Low-carb and fasted training increase sodium needs, because lower insulin levels make the kidneys excrete more sodium

How It Works

Four mechanisms explain why electrolytes matter for performance — and why getting them wrong hurts:

1
Fluid balance and plasma volume. Sodium is the main driver of how much water your body retains in the bloodstream. Adequate sodium maintains plasma volume, which keeps stroke volume and sweat capacity high. Losing more than ~2% of body mass as fluid measurably impairs endurance performance — and sodium is what makes the fluid you drink actually stay on board.1
2
Nerve conduction and muscle contraction. Every nerve impulse and muscle contraction depends on sodium and potassium moving across cell membranes, with calcium triggering contraction and magnesium enabling relaxation. When these gradients drift out of range, signalling becomes erratic — felt as twitching, weakness, and fading power output.
3
Cramp prevention. Exercise-associated cramps have multiple causes, but salty sweaters with large unreplaced sodium losses cramp more often — a pattern reported in field studies of tennis players and American football players prone to heat cramps. If you cramp late in long, hot sessions, sodium replacement is the first lever to pull.
4
Hyponatremia risk from overdrinking. The flip side: drinking aggressively beyond thirst with plain water dilutes blood sodium. A 2005 study in the New England Journal of Medicine found 13% of Boston Marathon finishers had some degree of hyponatremia, strongly associated with weight gain during the race from overdrinking.2 More water is not automatically better.

Why thirst alone can lag behind

Thirst is a reliable guard against overdrinking, but in long, hot events it can underestimate fluid needs once you are already dehydrated, and it tells you nothing about sodium. The practical approach: drink to thirst, and make sure what you drink during long sessions contains sodium. Weighing yourself before and after a typical session (1kg lost ≈ 1 litre of sweat) gives you a personal sweat rate to plan around instead of guessing.

Dosage & Timing

500–1000mg
Sodium per litre of sweat replaced
Heavy/salty sweaters: top end
60–90min
Session length where mixes pay off
Sooner in heat
~150%
Of fluid lost, rehydrated after
With sodium, over 2–4 hours

Pre, during, and post

  • Before: Start hydrated — roughly 5–7ml/kg of fluid in the 2–4 hours before training. Before long, hot sessions, a sodium-containing drink (or simply salting your pre-session meal) helps expand plasma volume.
  • During: For sessions over 60–90 minutes, drink to thirst with a mix providing 500–1000mg sodium per litre. Sweat also contains potassium (~200mg/L) and a little magnesium, so a complete mix covers the supporting cast.
  • After: Replacing only the water re-dilutes blood sodium and triggers urination before you're rehydrated. Aim for ~1.5x the fluid lost with sodium — from a mix or salted food — over the following hours.
  • Not sure how much you sweat? Get your fluid baseline with FitCalc's Water Intake calculator, then adjust upward for training days and heat.

Who actually needs electrolyte supplements?

  • Anyone training longer than 60–90 minutes, especially endurance athletes
  • People training in heat or high humidity, or who are not yet heat-acclimated
  • Heavy or salty sweaters — drenched kit, salt stains, stinging eyes
  • People on low-carb or ketogenic diets, where increased renal sodium excretion drives the fatigue and headaches of "keto flu"
  • Athletes doing two-a-days or cutting weight via sweat, where losses compound between sessions
Practical advice: For a hard 90-minute session, 500–750ml of fluid with ~500–1000mg sodium during, then salted food and fluids after, covers most people. A quarter teaspoon of table salt in a bottle (~575mg sodium) is the budget version of any commercial mix.
Caution: If you have high blood pressure, kidney disease, or take diuretics or blood pressure medication, get medical advice before deliberately increasing sodium intake.

Best Electrolyte Supplements

We prioritise: sodium content that actually matches sweat losses, sensible potassium and magnesium, minimal or zero sugar where appropriate, and transparent labelling.

#1
LMNT Electrolyte Drink Mix
1000mg sodium, 200mg potassium, 60mg magnesium per stick — one of the few mixes dosed for real sweat losses. Zero sugar, ideal for heavy sweaters and low-carb athletes.
1000mg sodiumZero sugarKeto-friendly
Check PriceView on Amazon
#2
Liquid I.V. Hydration Multiplier
~500mg sodium plus glucose to drive sodium-glucose co-transport in the gut. The carbs make it a strong choice during long endurance sessions and hot-weather events.
Glucose co-transportDuring-exercise carbsWidely available
Check PriceView on Amazon
#3
Nuun Sport Hydration Tablets
~300mg sodium per tablet with minimal sugar. Lighter dosing suits moderate sweaters and shorter sessions; tubes are cheap, portable, and easy to drop in any bottle.
Low sugarPortable tabletsGreat value
Check PriceView on Amazon
🔗 Disclosure: Some links above are affiliate links — if you buy through them, FitCalc may earn a small commission at no extra cost to you. Our rankings are based on research and ingredient quality, never commission rates. Learn more.

Frequently Asked Questions

Do I need electrolytes for every workout?

No. For sessions under about 60 minutes in moderate conditions, plain water plus the sodium in your normal meals is enough. Electrolytes become worthwhile for sessions longer than 60–90 minutes, training in heat or humidity, double sessions, or if you're a visibly heavy or salty sweater.

Isn't extra sodium bad for blood pressure?

Population sodium guidelines are written for sedentary people, not for athletes replacing measured sweat losses. Sodium taken to offset what you lose in sweat doesn't accumulate the way habitual dietary excess does. That said, if you have hypertension, kidney disease, or take blood pressure medication, talk to your doctor before adding high-sodium drink mixes.

Are sports drinks like Gatorade enough?

Traditional sports drinks are mostly sugar with relatively little sodium — typically around 450mg of sodium per litre, while sweat commonly contains 800–1500mg per litre. They're useful as a carbohydrate source during long events, but heavy sweaters often need a higher-sodium mix or additional salt to actually match losses.

Can I just add table salt to my water?

Yes — it's the cheapest option. Roughly a quarter teaspoon of table salt provides about 575mg of sodium, which covers many people for an hour of sweaty training. Commercial mixes add potassium and magnesium, flavouring, and convenient dosing, but salt plus a banana gets you most of the way there.

What is hyponatremia and should I worry about it?

Exercise-associated hyponatremia is dangerously low blood sodium, usually caused by drinking large volumes of plain water during long events while losing salty sweat. It's most common in slower marathon and ultra-endurance participants who overdrink. The fix is simple: drink to thirst rather than on a forced schedule, and include sodium during events lasting several hours.

References

This guide is built from peer-reviewed research. Key sources:

  1. Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS; American College of Sports Medicine. American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine & Science in Sports & Exercise. 2007;39(2):377–390. PubMed
  2. Almond CS, Shin AY, Fortescue EB, et al. Hyponatremia among runners in the Boston Marathon. New England Journal of Medicine. 2005;352(15):1550–1556. PubMed

About the Author

FM
Written by Filip Mesec

Founder of FitCalc. Filip researches and writes FitCalc's training and nutrition guides, building each one from the peer-reviewed literature cited above and flagging clearly where the evidence is limited or contested. FitCalc's guides are educational and are not a substitute for personalised advice from your doctor or a registered dietitian.