The science of sodium. Built for endurance.
The hub for everything Lytework knows about sodium loss, hydration strategy, and endurance physiology. Start here, then go deeper into the area that matters for you.
The variable most endurance athletes get wrong.
Endurance athletes obsess over carbohydrate and fluid volume. Sodium gets bundled into a sports drink and forgotten. But sodium loss varies more between athletes than almost any other physiological variable in endurance sport — and it's the one most often underdosed in long sessions and racing.
A fixed-ratio electrolyte product, by definition, cannot account for that variability. Lytework was built on the opposite premise: separate sodium from fluid, dose it precisely, scale it to the athlete and the conditions.
Sodium loss is the product of two highly individual numbers.
Sodium loss per hour = sweat rate × sweat sodium concentration. Both vary widely between athletes — which is why a single fixed-dose product structurally can't serve everyone.
Sweat rate. How much fluid you lose per hour. Driven by intensity, heat, humidity, body size, and acclimatisation.
Sweat sodium concentration. How much sodium per litre of sweat. Largely genetic, and measurable only by a sweat test. Visible salt marks are common and don't indicate a high concentration on their own. Whole-body values across 506 athletes (Baker et al., 2016).
Combined sodium loss. The two multiplied, which is why hourly sodium needs vary more than tenfold between athletes in the same race.
Why fixed-ratio drinks fail under load.
Electrolyte drinks bundle sodium into a fixed ratio with fluid, carbohydrate, and flavour. Convenient for short sessions — structurally limiting for endurance. If you need more sodium, you must drink more, which means more carbs, more fluid, more flavour fatigue.
Four pillars of endurance hydration.
The conceptual model Lytework uses to structure individualised hydration strategies. Each pillar is partly independent — and handling them as separate, interacting variables is what makes precision possible.
From this framework, Lytework builds practical protocols for marathons, Ironman, ultra running, and HYROX — translating the model into repeatable strategies for specific events.
When the run "falls apart."
Research consistently identifies sodium depletion, not carbohydrate insufficiency, as a primary driver of late-race decline. As plasma sodium falls, cardiovascular strain rises and pace becomes harder to hold.
When it's worth checking your sodium plan
- Feeling weak or flat in heat despite drinking to thirst
- Headaches or nausea late in long efforts
- A "sloshy" stomach where drinking more feels uncomfortable
- Racing in conditions meaningfully hotter than you've trained in
- Sessions extending well beyond your usual duration
These are prompts to review your plan, not evidence of a sodium deficit. Every one of them can be caused by heat stress, under-fuelling or pacing instead. Two cues we deliberately leave off this list: visible salt marks, which are common and don't predict how much sodium you lose, and cramping, which in real races tracks pace and prior cramp history rather than sodium.
The literature behind the framework.
Lytework is built on peer-reviewed research into sweat physiology, sodium variability, hydration strategy, and exercise-associated hyponatremia. Every source below is listed in full in Research Paper 001, including the work that argues against over-prescribing hydration. We publish the counter-evidence alongside the rest.
Sweat composition and sodium variability
Acclimation and population norms
Hydration, dehydration and performance
Sodium replacement, balance and hyponatremia
Full 22-reference list available in Research Paper 001, second edition. Every citation is verified against its source record.
Field trials, race conditions, ongoing research.
New writing from the Lytework team and athletes in the field.
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