Ultra-endurance events require specific strategies regarding hydration and electrolyte intake. Indeed, thermoregulation and the mechanical stresses associated with exertion lead to significant losses of water and electrolytes (minerals and vitamins) that must be replenished to maintain performance and limit the risk of nutritional deficiencies.
Understanding the Challenges of Hydration and Electrolyte Balance
During long-duration events, dehydration and hyponatremia are major risks that can directly affect the performance and health of athletes.
It is therefore crucial for athletes that water and electrolyte losses be compensated for through adequate hydration. It is necessary to avoid both underhydration and overhydration, which can lead to hyponatremia by increasing the dilution of sodium concentration in the blood. This electrolyte imbalance can have serious consequences for the athlete, ranging from simple cramps, nausea, and dizziness to a life-threatening emergency.
1. The Challenges of Hydration in Ultra-Endurance
Dehydration can seriously affect athletes' performance and health. Studies show that losing more than 2% of body weight in water leads to decreased physical and cognitive performance, as well as an increased risk of cramps, dizziness, and cardiac problems.
In ultra-endurance events, dehydration can occur rapidly, especially when races take place in extreme weather conditions. It is not uncommon for some athletes to lose up to 2 liters of sweat per hour of exertion. Furthermore, excessive fluid consumption without added sodium can lead to hyponatremia.
Key scientific data:
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Dehydration exceeding 2% of body weight compromises performance.
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The average sodium loss per liter of sweat is 0.5 to 2 g, varying according to the individual composition of the sweat.
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Hyponatremia occurs under conditions of overhydration, primarily when athletes consume excess water without compensating for sodium losses.
2. The Crucial Role of Electrolytes
Electrolytes, particularly sodium, play a central role in regulating fluid balance and muscle contraction. Sodium helps prevent hyponatremia and is essential for nerve and muscle function during prolonged exertion. Electrolyte losses vary depending on the individual, their training level, and climatic conditions, making an individualized approach essential.
Compensation recommendations:
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Sodium: The ideal intake is between 500 and 700 mg per liter of fluid, although requirements may increase depending on heat and perspiration. It is therefore advisable to use electrolytes, isotonic drinks, or gels containing sodium to compensate for losses.
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Other electrolytes (potassium, magnesium, calcium): Although less affected by perspiration than sodium, they contribute to proper cell function. Potassium intake (100-200 mg/liter) helps stabilize electrolyte levels during intense exercise.
3. Assess your perspiration to personalize your hydration
Since perspiration levels vary considerably between athletes, a personalized hydration strategy is essential.
To best assess their hydration needs, athletes can use the double weighing technique, ideally under conditions similar to those of the competition.
Double weighing technique:
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Weighing before and after exercise : weigh yourself before starting training and immediately after exercise under the same conditions (ideally in underwear).
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Calculating water loss : Calculate the difference in weight between the first and second weighings (subtracting the amount of water consumed during the session). This difference represents the water loss in liters.
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Adjusting fluid intake : The difference in weight will determine the amount of water needed during exercise to best compensate for fluid loss. Keep in mind that during races, it is recommended to replace approximately 80% of total fluid loss to avoid fluid overload.
For a long race, such as an ultramarathon in very hot conditions, this means consuming about 0.8 liters of water for every liter lost, adjusting intake according to conditions and duration of effort.
4. Differences between sensation of thirst, desire to drink and actual dehydration.
The sensation of thirst and the need to drink, while related, involve distinct mechanisms and are influenced by multiple factors, complicating the understanding of bodily signals during ultra-endurance events. Thirst is a physiological response to dehydration, triggered when the body detects fluid loss. The urge to drink, however, also depends on non-physiological elements, such as taste, the temperature of the liquid, and energy requirements.
Studies show that thirst can be influenced by dehydration levels, but also by subconscious responses and automatic adjustments of the central nervous system. This "dynamic complexity" integrates bodily signals and subjective perceptions, often processed without the athlete's conscious awareness. Thus, thirst is not always a perfect indicator of actual dehydration.
Source: Influences on thirst and drinking behavior during endurance exercise. All factors in this diagram are perceived, monitored, and/or regulated by the brain. ( 93.Armstrong LE, Giersch GEW, Dunn L., Fiol A., Muñoz CX, Lee EC Inputs to Thirst and Drinking during Water Restriction and Rehydration )
How should you react to thirst? For ultra-endurance athletes, understanding this distinction is crucial. While thirst indicates a need for fluids, it may not necessarily reflect the need to replenish lost electrolytes.
Therefore, it will be essential to follow a genuine hydration strategy adapted to one's rate of perspiration and associated electrolyte losses, instead of simply blindly following sensations of thirst.
5. Practical Tips for Hydration and Electrolyte Management
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Alternate between water and electrolyte-rich drinks (powdered electrolytes/tablets or sports drinks) to optimize hydration and maintain sufficient mineral and vitamin levels. Pay particular attention to sodium intake to adequately compensate for losses due to thermoregulation. The recommended sodium concentration for a sports drink is 500 to 700 mg/liter, but this can be adjusted for individuals with greater sodium loss.
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Consume 2 to 3 small sips every 10-15 minutes for gradual absorption, thus limiting the risks of overhydration or dehydration.
Examples of Hydration Strategies for Extreme Distances:
For an athlete whose sweat rate is 1 liter per hour of exertion, an ideal intake of 750 ml to 1 liter of fluid per hour with a sodium content of 500 to 700 mg (isotonic drink) is recommended. If fluid loss is even greater due to heat, a slight increase in sodium intake may be considered.
In ultra-endurance events, to meet electrolyte and energy needs, it will be essential to consume solid foods in addition to sports drinks (gels, fruit compotes, energy bars, dried fruit, etc.). This intake should be kept as regular as possible (every 30 minutes).
Conclusion
Hydration and electrolyte management is a fundamental aspect of nutritional strategy in ultra-endurance. Individual needs vary depending on perspiration rate, electrolyte loss, and race conditions, making individualized and structured preparation essential. By adapting fluid and electrolyte intake to each athlete's specific needs, it is possible to prevent the risks of dehydration and hyponatremia and optimize performance over long distances.
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