Lytework Labs Research Paper 001

The Physiology of Sodium Loss in Endurance Athletes

Implications for Hydration Strategy

A review of sweat physiology, sodium variability, and the implications for individualised hydration strategy in endurance sport. Introducing the SALT Hydration Framework.

Paper 001
Published March 2026
Author Lytework Labs
Pages 15 pages
References 24
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This paper reviews the physiology of sweat and sodium loss, the variability in sweat rate and sweat sodium concentration, and the combined impact on total sodium deficits during endurance exercise. It introduces the SALT Hydration Framework as a practical model for individualised hydration strategy.

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The Physiology of Sodium Loss in Endurance Athletes. Peer-reviewed references. Free to download.

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Executive summary

What the paper covers

A peer-reviewed synthesis of what the literature says about sweat physiology, sodium loss, and the case for individualised hydration.

Endurance exercise in triathlon, cycling, and distance running places a substantial thermoregulatory load on the body, driving high rates of sweating and significant loss of sodium in sweat. Sweat rate and sweat sodium concentration both vary widely between individuals, such that total sodium loss can range from less than 1g to more than 5–6g per hour in extreme cases.

This paper reviews the physiology of sweat and sodium loss, the variability in sweat rate and sweat sodium concentration, and the combined impact on total sodium deficits during endurance exercise. It then considers the implications for fluid balance, cardiovascular stability, performance, and the risks of hypohydration and hyponatremia.

Finally, it introduces the SALT Hydration Framework — Sodium, Amount, Load, and Timing — as a conceptual model for structuring individualised endurance hydration strategies.

Sweat sodium concentration can vary tenfold between athletes. A single hydration prescription cannot account for that.

Contents

What the paper covers

Eight sections moving from sweat physiology through to a working framework for endurance hydration.

  1. 01 Sweat Physiology
  2. 02 Sweat Rate Variability
  3. 03 Sweat Sodium Concentration
  4. 04 Estimating Sodium Loss
  5. 05 Implications for Hydration Strategy
  6. 06 Practical Applications for Endurance Athletes
  7. 07 The SALT Hydration Framework
  8. 08 Conclusion and References
Key findings

What the research shows

Three findings that define why individualised hydration matters more than universal guidelines.

10×
Variability in sodium loss between athletes

Sweat sodium concentration ranges from roughly 20–90 mmol/L across endurance athletes, with some salty sweaters exceeding 2.3 g/L.

5g+
Sodium loss in a single session

Athletes may lose up to 5g of sodium in one high-intensity session — and substantially more over longer or hotter events.

6×
Sweat rate variability between athletes

Sweat rate can vary more than sixfold between athletes in comparable conditions, ranging from 0.5 to over 3 litres per hour.

Peer-reviewed sources

All findings are grounded in peer-reviewed exercise physiology literature, including research from the Journal of Applied Physiology, Sports Medicine, and Clinical Journal of Sport Medicine.

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This paper is intended for educational purposes and reflects current understanding in exercise physiology literature. It does not constitute medical advice. Individual hydration needs vary — consult a qualified practitioner for personalised guidance.