Hydration and sodium for athletes who sweat heavily: when is water not enough?

Water is not always enough during prolonged, hot or very intense exercise, but an electrolyte drink is not automatically needed. Sweat rate and sweat sodium vary between people and conditions. Duration, heat and intensity matter, as do clothing, humidity, access to fluids and food. A sodium-containing drink can be relevant in some prolonged efforts with substantial water and sodium losses, but there is no universal dose. Commercial drinks are tools, not obligations: compare sodium, carbohydrate and portion information, and test tolerance in training. Drinking too much, even with sodium, can contribute to exercise-associated hyponatremia. Nausea, headache, confusion or vomiting during prolonged exercise require urgent medical assessment. People with uncontrolled hypertension, kidney or heart disease, relevant medication, pregnancy, and minors should seek professional advice before deliberately increasing sodium. Sweat-rate measurements can inform an individualized discussion, but they are method-sensitive and are not exact prescriptions.