Electrolytes – Hydration, Muscle Strength, and Nerve Function

Electrolytes are electrically charged minerals dissolved in body fluids that control vital functions. Sodium, potassium, magnesium, calcium, and chloride form the electrolyte balance, which regulates hydration, muscle contraction, nerve transmission, and pH balance.

The Five Main Electrolytes

Electrolyte	Normal Range (Serum)	Main Functions
Sodium (Na⁺)	135–145 mmol/L	Osmolarity, hydration, nerve impulse
Potassium (K⁺)	3.5–5.0 mmol/L	Heart rhythm, muscle contraction, membrane potential
Magnesium (Mg²⁺)	0.7–1.0 mmol/L	ATP synthesis, muscle relaxation, enzyme activity
Calcium (Ca²⁺)	2.2–2.6 mmol/L	Bones, muscle contraction, blood clotting
Chloride (Cl⁻)	96–106 mmol/L	Acid-base balance, osmolarity

Electrolyte Loss During Exercise

Sweat contains significant amounts of electrolytes – the composition varies greatly individually:

Electrolyte	Loss Through Sweat	Range of Variation
Sodium	500–1,500 mg/L sweat	Highest loss; large individual variations
Chloride	400–1,500 mg/L	Proportional to sodium
Potassium	120–400 mg/L	Significantly less than sodium
Magnesium	10–36 mg/L	Small but relevant during prolonged exertion
Calcium	15–20 mg/L	Small

Symptoms of Electrolyte Imbalances During Exercise

Hyponatremia (sodium deficiency): Excessive water drinking without salt replacement → headaches, nausea, confusion, life-threatening in severe cases (marathon risk)
Potassium deficiency: Muscle cramps, weakness, cardiac arrhythmias
Magnesium deficiency: Cramps, fatigue, sleep problems
General dehydration + electrolyte deficiency: Performance decline already at 2% body weight loss due to sweat

When Are Electrolyte Supplements Useful?

Situation	Recommendation
Training <60 min., normal	Water sufficient
Training 60–90 min. in heat	Electrolyte water or light electrolyte drink
Endurance >90 min.	Electrolytes + carbohydrates (30–60 g/h)
Keto/Low-carb diet	Increased electrolyte requirement (insulin lowers renal sodium retention)
Intermittent fasting	Electrolytes in the fasting window can help
Heat, sauna	Electrolytes before and after exposure

What to Look for in Electrolyte Supplements?

A good electrolyte supplement contains all important electrolytes in appropriate dosages, ideally without excessive sugar or artificial sweeteners. Sodium is the most important electrolyte during exercise – many products contain too little of it in favor of potassium.

Optimal composition per dose: Sodium 500–1,000 mg, potassium 150–300 mg, magnesium 100–200 mg, possibly small amounts of calcium and chloride.

Frequently Asked Questions (FAQ)

Is plain water alone sufficient for rehydration?

For short training sessions (<60 min.), yes. During long or intense sessions, pure water without sodium can even lead to dilution of sodium levels. Therefore: add electrolytes during long sessions.

Can too many electrolytes be harmful?

Overdosing on sodium (>10 g/day) can cause hypertension and renal strain. Potassium excess in renal insufficiency is dangerous. With normal kidney function and physical activity, the risk is low.