The Lab

The science of sodium. Built for endurance.

Everything Lytework knows about sodium loss, hydration strategy and endurance physiology, in one place.

Why sodium

The variable most endurance athletes get wrong.

Sodium loss varies more between athletes than almost any other variable in endurance sport. It is also the one most often underdosed. This page is the why. The session guide and the calculator are the how.

Endurance athletes obsess over carbohydrate and fluid volume. Sodium gets bundled into a sports drink and forgotten. But sodium loss is the product of two highly individual numbers, sweat rate and sweat sodium concentration, and both vary widely, which is why a fixed-ratio product structurally cannot serve everyone.

Research consistently identifies sodium depletion, not carbohydrate insufficiency, as a primary driver of late-race decline. Lytework was built on the opposite premise to the drink: separate sodium from fluid, dose it precisely, scale it to the athlete and the conditions.

0.5 to 2.0 L/hr

Sweat rate

Driven by intensity, heat, humidity, body size and acclimatisation.

420 to 1,630 mg/L

Sweat sodium concentration

Largely genetic. Whole-body values across 506 athletes (Baker et al., 2016).

200 to 3,300 mg/hr

Combined sodium loss

The two multiplied. Hourly needs vary more than tenfold between athletes in the same race.

The framework

Four variables. Four dials. Each set to you.

The model Lytework uses to build every individual hydration strategy. The four pillars interact, but each one is set to you on its own terms, and that is what makes precision possible. The session guide turns this into capsules per hour for real sessions and races.

Sodium

Electrolyte replacement

Match intake to a meaningful fraction of individual losses, not a fixed dose.

Amount

Fluid intake

Calibrated to limit body mass loss without overdrinking.

Load

Carbohydrate fuelling

Integrated with sodium and fluid. Avoid excessive osmolarity.

Timing

Nutrient delivery

Spread sodium, fluid and carbohydrate evenly across the session.

See the session guide

The research

The literature behind the dose.

Baker and colleagues (2016) tested 506 athletes and found whole-body sweat sodium ranging from roughly 420 to 1,630 mg per litre. There is no average to build a product around. If the loss is that individual, the dose has to be too.

Read the study

The 2019 update widened the dataset to 1,303 athletes and measured the rate of sodium loss by sport. Endurance athletes sat among the highest, losing sodium far faster than team-sport players. Across a long race that adds up, which is why Lytework sets the dose per hour, not per event.

Read the study

The National Athletic Trainers' Association position statement (2017) makes it a formal recommendation: quantify the individual's sweat rate, then build a replacement plan that fits them, sufficient but not excessive. Individualised dosing is not a marketing angle, it is the evidence-based standard.

Read the statement

The Third International Exercise-Associated Hyponatremia Consensus (2015) identified overdrinking beyond thirst as the most common cause of dangerously low blood sodium, and noted that hypotonic sports drinks will not prevent it. More fluid is not the answer. Dosing sodium, on its own and to the conditions, is.

Read the consensus

Research Paper 001

The full paper. Every source cited.

The Physiology of Sodium Loss in Endurance Athletes. Second edition, 15 pages, 22 verified references. Free to download.

Download the paper

The method

How your number is built.

Built with Oggi Zurzolo, Sports Performance Nutritionist

Most electrolyte products give you one fixed ratio and hope it fits every athlete. Lytework works the other way. The number you get is assembled from your own physiology, checked against the published research, and held inside hard safety limits before it reaches you. This is that build, in full.

Sweat rate

How much fluid you lose an hour, built from your body size, the heat, the humidity and how hard you go. A bigger athlete is scaled realistically, not assumed to sweat in proportion to their weight.

Weighted on established fluid-replacement guidance (ACSM)

Sweat sodium

How salty your sweat runs, from the profile you pick or your own sweat-test figure. The variable that differs most between athletes, several-fold, so it is never assumed from an average.

Baker et al. 2016, whole-body data from 506 athletes

Hourly loss

Your sweat rate multiplied by your sweat sodium. Two individual numbers, so the sodium you lose each hour is individual too. This is the figure a fixed-ratio drink can never know.

The target

We set out to replace a considered share of the loss, not every milligram, and we hold fluid below full replacement. Chasing everything, and drinking to match, is where the real trouble starts.

EAH consensus 2015 · NATA position statement 2017

Safety gates

Concentration ceilings and a mass-balance check cap every result inside physiologically sound limits. The tool will not return a dose or a fluid figure that tips you toward hyponatremia or gut failure. Safe first, then optimal.

Real racing

Every rule is pressure-tested against how a race actually unfolds. Field trials with endurance athletes, and years of the founder's own racing, because a number that works on paper still has to survive hour six.

The people

The people behind the numbers.

Lytework began with a question from Jon Sammut's own racing. Every part of his training was measured and planned, yet sodium was still a guess, and in the heat of an IRONMAN it was the guess that cost him. The calculator was built to answer that question properly, for every athlete rather than one.

Answering it properly took a sports nutritionist. Oggi Zurzolo, Lytework's nutrition advisor, worked on the calculator alongside Jonny: shaping the values it uses, testing its plans against real athlete profiles, and reworking the parts where the research and what athletes actually tolerate did not agree. Seven changes to the model came out of that work, and they are set out below.

Jonathan Sammut

Founder, Lytework Labs. Former professional triathlete who represented Australia and trained at the Australian Institute of Sport.

Oggi Zurzolo

Sports Performance Nutritionist and nutrition advisor to Lytework. Master of Sports Nutrition.

The calibration

7: changes to the model
1: checked and deliberately kept
3: test athletes, before and after

See what changed

The calibration

Where the research met practice.

Published research gives ranges, not answers. Sweat sodium alone varies several-fold between athletes, and the studies behind each range were run in different conditions, on different people. These are the points where Oggi's work moved the model, each one traced through real athlete profiles and verified on the live calculator.

Sodium replacement flexes.

A fixed share of sodium losses was too rigid. The model starts at 65% and moves within the 50 to 80% range athletes self-select: up for heat, salty sweat and long efforts, down for sensitive guts and ultra distance.

Widest-reaching change

Fluid steps down on long events.

Long-course athletes rarely replace a fixed share of fluid; the deficit grows with GI tolerance, missed bottles and pace. Fluid now sits at 70% under 3 hours, 65% from 3 to 10, and 55% beyond 10, while sodium holds steady. The old model did the opposite and asked for more fluid on the longest days.

Reversed the previous model

Carbs capped by the gut, not body weight.

Carbohydrate absorption is limited by intestinal transporters (SGLT1 and GLUT5), which can be trained but do not scale with body size. The cap is now 60, 90 or 110 g an hour by training level, and up to 120 for gut-trained athletes.

No longer multiplied by body mass

High sweaters no longer clipped.

The ceiling on modelled sweat rate rose from 2.5 to 3.0 litres an hour outdoors (2.8 indoors), so heavy sweaters in heat get plans built on their real losses.

Sweat-rate ceiling raised

A note when fluid cannot keep up.

On efforts of 3 hours or more at 1.8 litres an hour or more, the gut cannot absorb fluid as fast as it is lost. The plan now says so, and tells you to hold sodium steady, drink to thirst and manage pace and cooling.

New advisory

The cramp link, toned down.

The evidence connecting cramping to sodium loss is weaker than the model implied, so cramp history now nudges the estimate less, and the wording says the link is uncertain.

Cramp multiplier softened

Accuracy, stated honestly.

A flat ±15% claim overstated confidence. Plans now say they are within 15 to 25% for athletes who repeat-test in stable conditions, and that first estimates vary more.

Error band widened

Checked and left unchanged

The population sodium bands. They looked evenly spaced against a real distribution that clusters between 400 and 1,000 mg/L. On review they only describe where you sit, and they now feed the replacement adjustment, so moving them would change real sodium numbers for a cosmetic label. They stay as they are.

Before and after, three test athletes

Athlete	Sodium / hr	Fluid / hr	Carbs / hr
Olympic triathlon, 32°C, salty sweater75 kg, 2.5 h	1,900 → 2,200	1,150	98 → 90
Hard 5 hour race, 26°C92 kg, advanced	900 → 1,000	1,300 → 1,150	115
Ironman, 30°C, sweat-tested78 kg, 1.9 L/hr, 11 h	1,300 → 1,400	1,150 → 1,050	100

Sodium in mg, fluid in ml, carbohydrate in g. The typical athlete in a one to two hour session is unchanged: the review moved the edges, where the old model pointed the wrong way.

Six steps, each one traceable to the research or the road. What comes out is capsules per hour for your session, split per leg for triathlon. Build yours below.

Hydration intelligenceBuild your protocol.Sweat rate, sodium concentration, heat, duration. Two minutes, and the calculator turns them into capsules per hour you can actually run with.Open the calculator

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