CARDIO · HYDRATION
Sweat-Rate + Electrolyte Marathon Plan
Compute marathon sweat rate and a personalized fluid + sodium intake plan from a single training session.
Result
Hourly Fluid + Sodium Targets
Race-day fluid (ml) and sodium (mg) replacement per hour.
Hydration plan
- · Pre-race: 500 ml in the 3 h before the gun.
- · During: 460 ml/h target with 529 mg sodium.
- · Post-race: 3,450 ml within 6 h to replace sweat losses.
How to use it
- Open Sweat-Rate + Electrolyte Marathon Plan and enter your current baseline accurately.
- Adjust one variable at a time so changes are easy to interpret.
- Review the headline output first, then inspect supporting metrics.
- Run at least one conservative and one aggressive scenario.
- Use outputs to set your next training or nutrition action for the week.
- Save or share this setup if you want to revisit it later, then check one easier and one harder version before you change your plan.
Questions people usually ask
What is Sweat-Rate + Electrolyte Marathon Plan best used for?
Sweat-Rate + Electrolyte Marathon Plan helps you compute marathon sweat rate, fluid intake, and sodium replacement plan from a single training session. so you can turn estimates into practical next steps.
How do I avoid misleading results?
Use realistic baseline inputs, run multiple scenarios, and update assumptions as your training, recovery, or nutrition changes.
Is this medical advice?
No. Outputs are general planning estimates and do not replace professional medical guidance.
Is this free and private?
Yes. Tools run client-side in your browser with no signup.
Formula
See the math
The underlying formula with variables defined, derivation shown, and a worked example with units.
Related Resources
Learn the decision before you act
Every link here is tied directly to Sweat-Rate + Electrolyte Marathon Plan. Use the explanation, formula, examples, and benchmarks to pressure-test the calculator output from first principles.
How To Use
4 STEPSHow to Use Sweat-Rate + Electrolyte Marathon Plan
Step-by-step guide for the Sweat-Rate + Electrolyte Marathon Plan: inputs, interpretation, and reproducibility tips.
ReadFormula
6 VARIABLESMarathon Sweat Rate + Electrolyte Formula
Marathon hydration: sweat rate 0.5-2.5 L/h, sodium concentration 460-1840 mg/L. Casa 2007 + ACSM 2007 standards. Replace 70-90% of losses; avoid hyponatremia.
ReadRelated deep dive
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Long-form context behind the calculator output.
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Heat Acclimatization: Sodium and Plasma Volume
Heat acclimatization shifts plasma volume up 10-12% in 10-14 days. The sodium math that supports the adaptation and the workouts that drive it.
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Marathon Sweat Rate: 70kg Runner, 2% Body Mass Loss in Warm Conditions
Marathon sweat rate 0.57 L/h, total loss 2.3 L over a 4-hour temperate race. Body mass loss 2.1%, 460 ml/h fluid plan, 529 mg/h sodium target.
Read - Pillar·11 min
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Heart-rate zone methods compared: Karvonen, %HRmax, %HRR, lactate threshold — accuracy by training age, error bands, and which one for which goal.
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