Endurance Sports: Nutrition, Electrolytes, Caffeine, and Circulation

What is endurance, and how does it work?

Endurance refers to the body’s ability to sustain physical exertion over an extended period of time. It is based on two main physiological factors: maximum aerobic capacity (VO2max, or the maximum rate at which muscles can utilize oxygen) and the lactate threshold (the intensity at which lactate accumulates faster than it is eliminated). VO2max is the most predictive indicator of endurance performance, but running economy and resistance to central muscle fatigue also play a crucial role. These capabilities are developed through specific training: long runs at a moderate pace foster cardiovascular and metabolic adaptations, while high-intensity intervals push back the lactate threshold.

What is the optimal nutritional strategy for endurance?

Nutrition for endurance sports is dominated by carbohydrate management, the primary fuel for aerobic exercise lasting longer than 60 minutes. Here are a few fundamental principles:

• Pre-competition glycogen loading: Increase carbohydrate intake (8 to 12 g/kg/day) in the 24 to 48 hours before the event to maximize muscle and liver glycogen stores.
• In-exercise fueling: For efforts lasting more than 60 to 90 minutes, consume 30 to 60 g of carbohydrates per hour (up to 90 g/hour with a glucose-fructose blend). Gels, bars, bananas, or isotonic drinks are the most common sources.
• Post-exercise protein: 20 to 40 g of complete protein within 2 hours after exercise to initiate muscle repair and replenish glycogen.

Why are hydration and electrolytes essential?

Dehydration is one of the most well-documented limiting factors in endurance sports: a 2% loss of body weight in water reduces performance by 10 to 20%. Electrolytes —sodium, potassium, magnesium, and chloride—are lost through sweat and must be replaced to maintain intracellular fluid balance, prevent cramps, and support muscle contractility. Sodium is the most critical electrolyte during long-duration endurance events (> 2 hours): its absence from nutrition stations can lead to dilutional hyponatremia, a medical emergency sometimes observed in marathons. Isotonic beverage formulas balanced in glucose and salt are the gold standard.

Which dietary supplements improve endurance?

Several supplements have a strong evidence base for endurance sports:

• Caffeine: A dose of 3 to 6 mg/kg taken 60 minutes before exercise improves performance by 2 to 4% by reducing the perception of exertion and delaying central fatigue.
• Coenzyme Q10: a cofactor in the mitochondrial respiratory chain, it improves the efficiency of aerobic energy production and may reduce chronic muscle fatigue.
• Spirulina: rich in the antioxidant phycocyanin, bioavailable iron, and complete proteins. Several studies suggest an improvement in aerobic endurance and a reduction in post-exercise oxidative stress.
• Magnesium: contributes to energy metabolism and the reduction of fatigue. Increased sweating during endurance exercise raises magnesium requirements.

What role does sleep play in endurance performance?

Sleep is particularly crucial for endurance athletes. During deep sleep phases, training-induced cardiovascular adaptations (increased cardiac volume, densification of muscle capillaries, and proliferation of mitochondria) are consolidated. Sleep deprivation reduces VO2max, impairs thermal regulation during prolonged exercise, and increases the subjective perception of exertion. A post-workout nap (20 to 30 minutes) is a proven strategy for athletes with high training volumes, allowing them to enhance adaptations without overloading the central nervous system.

How can blood flow and muscle oxygenation be optimized?

Blood circulation delivers oxygen and energy substrates to active muscles. Several approaches can optimize this oxygenation:

• Beet juice (nitrates): converted into nitric oxide (NO), a vasodilator that improves blood flow to the muscles and reduces the energy cost of exercise. Consuming 300 to 600 mg of nitrates 2 to 3 hours before exercise significantly improves endurance performance.
• Iron: essential for hemoglobin synthesis. A deficiency—common among long-distance runners—leads to a decrease in VO₂max and chronic fatigue. Regular blood tests are recommended for high-mileage endurance athletes.
• Antioxidants (vitamin C, polyphenols): help limit chronic oxidative stress, which damages mitochondria and reduces aerobic capacity over the long term.