Hey there,

Sweat is ~99% water. The other ~1% is electrolytes, mainly sodium (plus chloride/potassium). That 1% is what usually gets missed.

Here’s the important part: intensity changes your electrolyte losses, not just duration.

Baker et al. (2019) compared two 90-minute sessions and found sweat sodium loss jumped 137.5% (from 659 mg to 1565 mg) when intensity increased from low (45% VO₂max) to moderate (65% VO₂max). In simple terms: the harder the session, the saltier your sweat becomes.

So:

Water is fine for short, easy work.
Long or hard sessions need electrolytes, not just fluid.

Practical rule: for long, hard runs, aim for 1–2 Core Hydration sachets per hour, this'll provide you with 500mg-1000mg of Sodium.

If you want zero prep, grab a Cadence Core Hydration Drink.

One of my favourites on site right now is the Starter Hydration System. For just $77 you'll get:

30 Electrolyte Sachets
12 Hydration Cans
A Bottle
A Free Cadence Cap
A Free Half Marathon & Marathon Fuel Guide

It's the ideal & best value bundle to prep you for all intensity levels of training.

Get Started Here

Matt

Head of Nutrition

usecadence.com

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The Science of Sweat