What is the recommended hydration protocol for healthy athletes before, during, and after exercise, including fluid volumes and electrolyte considerations?

Hydration Protocol for Athletes

Athletes should drink 6 mL of fluid per kilogram of body weight every 2-3 hours before exercise, minimize body water losses during exercise without gaining weight, and replace 100-150% of body mass losses after exercise with fluids containing sodium, carbohydrates, and protein. 1

Pre-Exercise Hydration

Start exercise in a euhydrated state by consuming 6 mL/kg body weight every 2-3 hours before training or competition. 1 For a 70 kg athlete, this translates to approximately 420 mL every 2-3 hours. This protocol ensures adequate hydration while allowing time for urine excretion before exercise begins. 2

Monitoring Pre-Exercise Hydration Status

You can confirm adequate hydration using these objective markers: 1

• Daily body mass changes <1% (measured post-void, nude, in the morning)
• Urine specific gravity <1.020 (first morning urine preferred)
• Plasma osmolality <290 mmol/kg

The first morning urine is the most reliable assessment point since exercise, diet, and prior drinking influence urine concentration measurements throughout the day. 1

During Exercise Hydration

Minimize body water mass losses during exercise without increasing body weight to reduce physiological strain and preserve performance. 1 The goal is to match fluid intake as closely as possible to sweat losses, though complete replacement is often impractical. 3

Fluid Volume During Exercise

Drink small amounts frequently (150-300 mL every 15-20 minutes) rather than large boluses, adjusting based on individual sweat rate. 4 Sweat rates typically range from 1.0-1.5 L/h during vigorous exercise in hot environments, though some athletes exceed 2.5 L/h. 1

Sodium Supplementation During Exercise

For exercise lasting longer than 1 hour, consume fluids containing 0.5-0.7 g/L of sodium. 1, 2 This concentration enhances palatability, promotes fluid retention, and prevents hyponatremia in susceptible individuals. 2

If experiencing muscle cramping, increase sodium supplementation to 1.5 g/L of fluid. 1 Athletes who are "heavy sweaters" or notice salt crusts on skin and clothing should deliberately increase sodium intake before, during, and after exercise. 1, 5

A critical caveat: Public health recommendations regarding sodium restriction do not apply to athletes losing large volumes of sodium through sweat. 1 Inadequate sodium replacement can result in deficits that trigger muscle cramping during prolonged exercise. 1

Carbohydrate Supplementation During Exercise

Include 30-60 g/h of carbohydrates for exercise lasting longer than 1 hour, increasing to 90 g/h for events exceeding 2.5 hours. 1 This can be achieved through a combination of fluids and solid foods. 1

For practical implementation, drinking 600-1200 mL/h of solutions containing 4-8% carbohydrates provides both adequate fluid and carbohydrate delivery. 2, 6 The carbohydrates can be glucose, sucrose, or maltodextrin. 2

Post-Exercise Rehydration

Replace 100-150% of body mass losses with fluids and electrolytes after exercise. 1 The higher percentage (150%) accounts for ongoing urinary losses during the rehydration period. 1

Aggressive Rehydration Protocol

If rapid replenishment is needed (within 1 hour post-exercise), aim for 150% replacement of body mass losses. 1 However, this may not be achievable for all athletes due to time constraints or gastrointestinal discomfort, making 100-120% replacement more realistic. 1

Optimal Recovery Fluid Composition

The preferred rehydration method combines fluids with foods, particularly salty foods. 1 Recovery hydration should include: 1

• Sodium (to maintain total body water and replace sweat losses)
• Carbohydrates: 0.8 g/kg/h (consumed within the first hour to maximize muscle glycogen resynthesis)
• Protein: 0.2-0.4 g/kg/h (to maximize protein synthesis rates and improve fluid balance restoration)

Drinks like chocolate milk, with a 4:1 carbohydrate-to-protein ratio plus sodium, are particularly effective for post-exercise rehydration. 1 These combination beverages restore fluid balance more effectively than standard carbohydrate-electrolyte sports drinks alone. 1

Special Considerations and Common Pitfalls

Avoiding Overhydration

While dehydration impairs performance, recreational athletes should be cautious not to overhydrate during exercise, as this can lead to hyponatremia. 1 Never drink at rates exceeding sweat rate, and body weight should not increase during exercise. 3

Multi-Day Competitions

For competitions lasting several days (cycling stage races, tennis tournaments), monitor hydration status daily using morning body mass and urine specific gravity. 1 Establish baseline body mass by measuring post-void nude weight on consecutive mornings after consuming 1-2 L of fluid the prior evening. 1

Temperature Considerations

Fluid temperature between 15-22°C (59-72°F) enhances palatability and promotes greater fluid consumption. 2 Flavored beverages further improve voluntary intake. 2

Exercise Duration Under 1 Hour

For exercise lasting less than 1 hour in temperate conditions, water alone is generally sufficient. 4 Carbohydrate-electrolyte solutions show little performance advantage over plain water in this duration. 2