Hydration for Endurance: Why One Drink Isn’t Enough (and What Actually Works for Women)
Trail Note
This Trail Note is informed by current endurance physiology and hydration research. Footnotes are included for those who wish to go deeper.
Hydration for Endurance: Why One Drink Isn’t Enough (and What Actually Works for Women)
Hydration is often treated as a moment.
Bottles filled at the trailhead. Vests packed the night before. A last-minute check on race morning.
But hydration status is not created in a single session. It is cumulative. It reflects the days before, the weeks of training, and the conditions your body has been adapting to quietly in the background.
For women in endurance and trail environments, hydration is rarely just about fluid volume. It is about balance.
Why women’s hydration needs are different
When we sweat, we lose more than water. Sodium, potassium, magnesium and calcium leave the body alongside it. These electrolytes support fluid retention, nerve signalling and muscle contraction. But the rate and concentration of that loss varies enormously between individuals.
Research shows women often have lower whole-body sweat rates than men at comparable workloads, yet sodium concentration in sweat can be similar or, in some cases, higher1. Importantly, variability between individuals far exceeds the average difference between sexes, with sweat sodium concentration differing by more than 80 mmol/L across athletes2.
This creates a distinct challenge: less total fluid loss, but potentially similar electrolyte depletion.
In practical terms, this is why many women try to fix fatigue by drinking more water and end up feeling worse. Sloshy stomachs, bloating, headaches, dizziness, or unexplained heaviness late in a run are often signs that fluid intake is outpacing electrolyte replacement.
Women are also at higher risk of exercise-associated hyponatremia, a condition caused by overconsumption of low-sodium fluids during prolonged exercise, particularly in hot conditions or technical terrain where cognitive load is high3.
Common signals and what they often indicate
| Signal | What it often indicates | Possible problem-solving approach |
|---|---|---|
| Bloated or sloshy stomach | Fluid intake exceeding electrolyte replacement | Temporarily reduce plain water intake, increase electrolyte concentration, and allow absorption to settle before adding more volume |
| Headache despite drinking | Possible sodium dilution or low plasma sodium | Shift focus from total volume to balance, adding sodium via electrolytes rather than increasing overall fluid intake |
| Flat legs or poor coordination | Cumulative hydration and fuel imbalance | Layer carbohydrates alongside hydration, review intake earlier in the session, and consider cumulative fatigue, heat load, or terrain demands |
These signals are not diagnostic. They are information. Patterns over time matter more than any single moment.
Hormones change the equation
Hormonal fluctuations across the menstrual cycle influence fluid regulation, thermoregulation, cardiovascular strain and perceived exertion4.
Progesterone, which rises in the luteal phase, increases core temperature and can alter thirst signals. Estrogen, more dominant earlier in the cycle, supports fluid retention and may improve tolerance to heat stress5.
This is why a hydration strategy that worked well a few weeks ago can suddenly feel intolerable, even when pace, weather and terrain appear unchanged. The body has not become unpredictable. The internal environment has shifted.
Why isotonic drinks support efficient hydration
Isotonic drinks are formulated to closely match the body’s natural fluid balance. Rather than forcing hydration through high concentration, they support steady intake and gastric emptying.
Carbohydrate–electrolyte solutions have been shown to improve fluid absorption and can enhance endurance performance by approximately 9–18 percent compared to water alone, largely through improved tolerance and sustained energy availability6.
PURE Electrolyte Hydration: where it fits
PURE Electrolyte Hydration is formulated as an isotonic sports drink designed to support fluid absorption and baseline electrolyte replacement during exercise.
It is not intended as a high-sodium loading solution. Instead, it functions as a foundational layer that can be scaled using gels, food, or higher-density race fuels as training demands, heat exposure, or duration increase.
Hydration works best as layered support
Hydration is most effective when approached as a system rather than solved by a single product.
Fluid supports volume. Electrolytes support retention and nerve function. Carbohydrates reduce physiological stress and improve absorption.
Research on prolonged endurance exercise suggests that partial sodium replacement, rather than attempting to fully match losses, is often sufficient and better tolerated. For women maintaining fluid balance during multi-hour efforts, sodium intakes of approximately 500–700 mg per hour may help reduce hyponatremia risk without excessive gastrointestinal burden7.
This layered approach allows hydration strategies to adapt to terrain, heat, hormonal phase and training load without unnecessary complexity.
Hydration is not about control.
It is about creating conditions where the body can respond rather than compensate.
Footnotes
- Baker LB. Sweat sodium concentration: variability and implications for hydration strategies. Sports Medicine.
- Hew-Butler T et al. Sodium supplementation and exercise-associated hyponatremia. British Journal of Sports Medicine.
- Rosner MH. Exercise-associated hyponatremia in female endurance athletes. Clinical Journal of Sport Medicine.
- Charkoudian N, Stachenfeld NS. Sex hormone effects on thermoregulation. Journal of Applied Physiology.
- Notley SR et al. Menstrual cycle phase and heat tolerance. Sports Medicine.
- Burke LM et al. Carbohydrate–electrolyte solutions and endurance performance. Journal of Sports Sciences.
- Hoffman MD et al. Sodium intake during prolonged endurance exercise. Clinical Journal of Sport Medicine.
