Dial In Your Hydration: Sweat, Sodium and the Gut
Trail Notes | Fuelling & Hydration
Dial In Your Hydration
sweat, sodium and the gut.
Hydration is one of the most individual parts of endurance running, and one of the easiest to get wrong. The good news is that it is learnable, long before race day.
Hydration is individual
Sweat rates vary enormously. In one sweat test, two runners in the same conditions lost wildly different amounts, one around 1.8 litres an hour, the other around 0.2. Generic advice like drink this much every hour cannot account for that.
Your needs shift with your body, your pace, the weather and the day.
A cold start and a hot afternoon are not the same. A good plan gives you a starting point and teaches you to adjust.
Sodium matters
Sodium concentration in sweat also varies hugely. Salty sweaters need significantly more. It helps maintain fluid balance, nerve function and muscle contraction, and under-replacing it makes cramping, nausea and poor fluid absorption more likely.
Some runners need one electrolyte tablet in a bottle. Others need two or three. The point is to find your own number.
Do not just drink more plain water
Drinking large amounts of plain water without enough sodium can dilute your blood sodium and leave you feeling worse, not better. The answer is not simply more water. It is fluid plus electrolytes.
Separate fluid from fuel
You do not have to drink your calories. Take energy from gels, bars or food, then adjust your fluid separately based on sweat, thirst and temperature. This gives you far more control across a long day.
Her Trails coaching cue
Your gut is trainable. Use long runs to rehearse how much fluid and sodium you can tolerate, in heat and cold, on climbs and descents. Mistakes in training are useful. Mistakes on race day are much harder to fix.
Written by the Her Trails coaching team
Trail Notes are evidence-informed coaching journals written for women who train, race and run on trails.
Go deeper inside Her Trails
Watch Dial It In: Hydration and Fuelling for Endurance in Base Camp, and pair it with How to Hydrate as a Runner.
