Hydration Strategy for Ultra Marathons

Ultra marathon success depends heavily on proper hydration. This guide covers the science of sweat rate, sodium replacement, and preventing hyponatremia.

Understanding Sweat Rate

Calculating Your Sweat Rate:

1. Weigh yourself nude before a 1-hour run
2. Run at goal pace in similar conditions
3. Weigh yourself immediately after (nude, toweled off)
4. Weight loss in pounds = sweat rate in pounds/hour

Example: 150 lb runner loses 1.5 lbs in 1 hour = 1.5 L/hour sweat rate

Hydration Guidelines for Ultras

Target Fluid Intake: 400-800ml per hour (adjust for conditions)

• Hot conditions: Higher end
• Cool conditions: Lower end
• Never drink more than you can absorb (~1000ml/hour)

Electrolyte Strategy:

• Sodium: 300-700mg per hour
• Potassium: 80-200mg per hour
• Magnesium: 10-20mg per hour
• Prevents hyponatremia and muscle cramping

Preventing Hyponatremia

Dangerous condition from drinking too much fluid without electrolytes:

• Symptoms: Nausea, dizziness, confusion
• Prevention: Match fluid intake to sweat rate
• Include sodium in every aid station meal
• Drink to thirst, not to a rigid schedule

Ultra-Specific Strategies

50K (7-10 hours)

• Hydrate every 15 minutes: 150-200ml
• Electrolyte supplement every 30 minutes

100 Miles (18-30+ hours)

• Crew support critical for consistent fueling
• Calculate fuel/hydration in advance
• Plan for changing conditions
• Consider mouth swishing (50-60 second swish of carbs)

Research: Ultramarathon Medicine (Hoffman), Hyponatremia in Endurance Sport

[Infographic: Sweat Rate Calculator] [Chart: Hydration Protocol by Distance] [Image: Electrolyte Sources] [Timeline: 100-Mile Fueling Strategy]