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Hydration Semantics: Why Words Matter in Endurance Sports

Recently, while running up Pikes Peak, I overheard a conversation that perfectly illustrates the confusion around hydration. A well-meaning runner told a woman new to mountain racing:

“You don’t need to carry water during the race, they have plenty of aid stations. Most people over-hydrate anyway.”

The intent was good, but the message was misleading. For someone unfamiliar with the science and semantics of hydration, over-hydration could mean either “drinking too much plain water” or “drinking too much fluid in general.” Those are not the same thing—and misunderstanding the difference can have real consequences for athletes.

Dehydration vs. Hyponatremia

Two common hydration-related conditions are often confused:

  • Dehydration: Insufficient fluid intake that leads to total body water loss. Even a 2–3% reduction in body weight from fluid loss can increase perceived exertion, core temperature, and heart rate.
  • Exercise-Associated Hyponatremia (EAH): A condition caused by dangerously low blood sodium levels, usually from drinking excessive amounts of water (or sometimes electrolyte beverages) without replacing sodium. Symptoms may include bloating, nausea, vomiting, or a “puffy” appearance.

The media has often lumped these together, leading athletes to believe the symptoms—and the risks—are the same. They are not.

Why Semantics Matter

For experienced athletes, “hydration” often means a balance of water and electrolytes. But for a new runner, cyclist, or triathlete—especially at altitude—telling them simply to “hydrate” without clarifying what that means can be dangerous.

Dr. Tim Noakes, once a leading voice behind early hydration guidelines, reversed many of his recommendations in his book Waterlogged (2012). While his work remains debated, it helped highlight the importance of precision in language around hydration.

Sweat Rates and Sodium Variability

Monitoring sweat rate can be helpful, but it’s not a perfect measure. Factors such as respiratory water loss, metabolic water production, and glycogen breakdown make the math tricky. Still, tracking sweat rate in different environments can help athletes spot trends.

Sodium loss is even more variable. On average, athletes lose 400–500 mg of sodium per pound of sweat—but it can range as high as 1100 mg. This makes blanket recommendations about salt tablets difficult. Some studies show sodium supplementation doesn’t prevent sodium loss or improve performance, but it may reduce overall weight loss during ultra-endurance events (Hew-Butler 2006; Speedy 2002).

Practical Hydration Guidelines

So what does this mean for athletes training or racing in hot, humid, or high-altitude environments?

KEY POINTS:

  • Don’t chase “zero loss.” Trying to perfectly match fluid intake with sweat loss often backfires. Some body mass loss is normal.
  • Use sweat rate trends, not exact math. Weighing before and after workouts helps you learn your personal range, but don’t obsess over ounces.
  • Train your tolerance. Acclimatization is as important as fluid intake. Sweating earlier and more efficiently is a sign of improved fitness.
  • Replace after big sessions. If you lose >2% of body weight, replace fluids gradually over 24–48 hours. Aim for ~24 oz (750 ml) per pound lost, spread throughout the day.
  • Think beyond water. Electrolytes (sodium, chloride, potassium, magnesium, calcium) and glycogen replenishment both improve hydration status. For every gram of glycogen stored, ~3 grams of water are pulled into muscle cells.
  • Listen to thirst—with context. Thirst works well for shorter, lower-intensity efforts. In long races, fatigue and energy depletion can blunt thirst cues—so plan ahead.
  • Use carbohydrate-electrolyte drinks. They improve palatability, stimulate thirst, and help maintain sodium balance.

 cross published: Trifuel

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