Hydration in long trail running is not just about drinking water. It is about replacing enough fluid and sodium to stay functional as conditions, duration, and sweat losses increase. This episode explains why runners can drink plenty and still feel flat, thirsty, heavy, or cramp-prone when sodium intake does not match the demands of the session. It also unpacks the simple idea that water replaces volume, but sodium helps you retain and use that fluid effectively.

The episode then shows how this appears in real training, why many runners get it wrong by using the same plan in every condition or by drinking too much plain water, and how to build a more practical strategy based on weather, duration, and individual sweat loss.

Main takeaway: Hydration is not just water. On long runs, replace what you sweat, not just what you drink.

Key references:

1. American College of Sports Medicine. Exercise and Fluid Replacement.

2. World Athletics. Fluid Needs for Training, Competition, and Recovery in Athletes.

3. Gatorade Sports Science Institute. Hydration and Nutrition Considerations for Endurance Exercise in the Heat.

4. Gatorade Sports Science Institute. Sodium Ingestion, Thirst, and Drinking During Endurance Exercise.

5. Gatorade Sports Science Institute. Sweating Rate and Sweat Sodium Concentrations in Athletes: A Review of Methodology and Intra-/Interindividual Variability.

6. ACSM. 9 Facts About Hydration & Electrolytes.

7. Gatorade Sports Science Institute. Normative Data for Sweating Rate, Sweat Sodium Concentration, and Sweat Sodium Loss in Athletes.

8. Gatorade Sports Science Institute. Sodium-Free Fluid Ingestion Decreases Plasma Sodium During Exercise in the Heat.