Hydration, sweat and electrolytes for endurance

Hydration guidance for athletes went from drink as much as possible to drink to thirst, and the current position is more nuanced than either.

What dehydration does

Fluid loss above roughly two percent of body mass is associated with measurable impairment in endurance performance, increased cardiovascular strain and increased perceived effort.

Effects are more pronounced in heat. Effects on strength and short high-intensity efforts are smaller.

What overdrinking does

The more dangerous error, and the one that changed the advice.

Drinking large volumes of hypotonic fluid while losing sodium through sweat can dilute blood sodium concentration, producing exercise-associated hyponatraemia.

Symptoms range from nausea and headache to confusion, seizures and death. They overlap with dehydration symptoms, which makes it dangerous, because the instinctive response of drinking more makes it worse.

It occurs most often in slower participants in long events who drink at every station out of diligence.

Deaths have occurred. This is the reason drinking as much as possible is no longer recommended.

The current approach

Start sessions hydrated. Normal drinking through the day.

During exercise, drink according to individual sweat rate rather than a fixed schedule.

Sweat rates vary enormously between individuals — from a few hundred millilitres per hour to well over two litres in some people in heat.

A fixed recommendation cannot serve both.

Measure your own. Weigh yourself naked before and after a session of known duration, accounting for any fluid consumed. Weight lost plus fluid consumed, divided by hours, gives your sweat rate for those conditions.

Do this in different conditions, since heat changes it substantially.

This is the single most useful thing an endurance athlete can do about hydration and almost nobody does it.

Aim to limit losses to under about two percent of body mass, rather than to replace everything.

Do not drink beyond thirst in the absence of a specific reason.

Sodium

Sweat contains sodium, and sodium concentration in sweat varies enormously between individuals — some people are markedly salty sweaters, visible as white residue on clothing and a salty taste.

Replacing sodium matters for:

Sessions over roughly two hours.

Hot conditions.

High sweat rates.

Salty sweaters.

Multiple sessions in a day.

Anyone with a history of cramping or of hyponatraemia.

Sodium also improves fluid retention, which is why rehydration after a session is more effective with sodium than with plain water.

For plant-based athletes specifically: whole-food diets are generally lower in sodium than diets containing processed foods, since most dietary sodium comes from processed products.

Which means an athlete eating mostly home-cooked plant food may have a lower baseline sodium intake and may need to be more deliberate about replacement.

Salt your food. This is not the population you were thinking of when you decided to reduce salt.

Practical sources

Commercial electrolyte products, which are convenient and mostly sodium with some potassium and magnesium.

Sports drinks, which provide sodium and carbohydrate together.

Salt added to food and to home-made drinks.

Salty snacks during long events — pretzels, salted nuts, olives.

Home-made: water, a pinch of salt, some sugar or fruit juice, and lemon. This works and costs almost nothing.

Cramps

Traditionally attributed to dehydration and electrolyte loss. The evidence is more equivocal than that framing suggests.

Current thinking gives more weight to neuromuscular fatigue as a cause, with dehydration and electrolyte status as contributing factors in some cases.

Practically: for athletes who cramp, adequate sodium is worth addressing, and so is training load, pacing, and conditioning for the specific demands.

Pickle juice has some evidence for acute cramp relief, apparently through a reflex response in the mouth rather than through electrolyte content, which is an odd and reasonably well-supported finding.

Caffeine

One of the best-evidenced performance aids available, with substantial evidence for endurance, and it is plant-based by default.

Doses in the region of three to six milligrams per kilogram, taken around an hour before, are the usual research protocol.

The mild diuretic effect does not cause dehydration in habitual consumers at ordinary doses.

Individual sensitivity varies considerably, and the effect on sleep persists longer than people expect.

Beetroot juice

Worth mentioning as a plant-based ergogenic aid with real evidence.

Dietary nitrate improves efficiency and endurance performance in several studies, with effects being more pronounced in recreational than in elite athletes.

Concentrated beetroot juice shots, taken two to three hours before, are the usual protocol.

One practical note: antibacterial mouthwash reduces the effect, because the conversion of nitrate to nitrite depends on bacteria in the mouth.

General information rather than individual advice. Symptoms of confusion, severe headache or nausea during prolonged exercise require immediate medical attention. Do not force large volumes of plain water.