Some runners over-hydrate by continuously drinking large amounts of water, which dilutes the remaining sodium in their blood. According to clinical data from Mayo Clinic, this leads to hyponatremia. Initial symptoms include mild cramps and nausea, but continued consumption of plain water can escalate the condition to water intoxication, causing dizziness, muscle spasms, and complete exhaustion.

When running in high temperatures, the cardiovascular system diverts about 1,5 to 2 liters of blood per minute away from the stomach and active muscles. This blood is redirected closer to the skin's surface to promote sweating and cool the body, keeping the core temperature safe. This creates a challenge for runners. First, reduced blood flow to muscles means less oxygen, forcing the heart rate to increase. Second, significantly decreased blood circulation to the stomach accelerates the body's glucose consumption. As runners sweat extensively to cool down, they lose not only water but also essential electrolytes, primarily sodium.

Over-hydrating during and after a run can lead to abdominal pain and exhaustion for runners. *Marathon Handbook*

To prevent this condition, runners must follow a structured hydration plan rather than relying on instinct. Research from running nutrition specialists at Featherstone Nutrition and Reno Running Company suggests a time-quantified fluid and electrolyte intake regimen.

For short runs lasting under 45 minutes, the body typically does not experience significant energy depletion. However, if the dew point (humidity index) is high, runners should carry a handheld water bottle containing a light electrolyte solution and sip small amounts from the first kilometers.

When runners undertake longer workouts, from 45 to over 60 minutes, the challenge intensifies. This is when the body's glucose reserves drop sharply. To maintain stamina, runners need to supplement with 30 to 60 grams of liquid carbohydrates per hour through specialized sports drinks. For professional or ultra-endurance runners, this tolerance threshold can reach 90 to 100 grams.

However, this fluid and electrolyte intake is only effective if consumed at the correct level and frequency. Avoid drinking large quantities of water at once, as the stomach's digestive function is limited and cannot process it quickly enough. Instead, divide the liquid intake, supplementing regularly with 300 to 700 ml every 15 to 20 minutes in small sips to allow the body to absorb it effectively.

Crucially, the entire process hinges on prioritizing sodium. Completely replacing plain water with high-sodium ion and electrolyte drinks helps directly replenish the salt lost through sweat, while also preventing water retention that can cause stomach sloshing.

While "listening to your body" is common advice for new runners, the paradox of hydration during running is that instinct often misleads. Feelings of exhaustion and cramps do not always signal a lack of water; more often, they indicate a sodium deficiency. Drinking more plain water to address these symptoms can worsen the condition.

Duc Anh

The VnExpress Da Nang International Marathon Herbalife Cup 2026, scheduled for 19/7, is a large-scale international race part of the VnExpress Marathon series. The course takes athletes across iconic bridges and coastal roads embracing Da Nang Bay. Registration is currently open for the Regular phase; interested runners can sign up here.