Fluid and Fuel Considerations for Marathon Running

by Clare Wood, Sports Dietitian

Carbohydrate Intake

For optimal performance during any event that is more than 90 minutes in duration, such as a marathon, it is crucial to take in carbohydrate during the race. Doing this will minimize fatigue, and spare muscle glycogen during the race so that muscle fuel stores will last longer.

TIP

Practice strategies for your race during training, such as various pre-race meals, and various foods and fluids during training

The maximum rate for stomach uptake and metabolism of glucose for use in the muscles is approximately 1g/kg body-mass/hour. So for an athlete of about 70kg, this would be 70g/hour. For some people it is difficult to take this amount in during a race, so this guideline is an upper limit.

Hydration

Hydration is vitally important for optimal performance and health, particularly in hot and/or humid conditions. Your level of fluid intake is dependant on your specific sweat rate (see calculating sweat rate). However, for a guide, taking in about 200ml every 20 minutes is the current guidelines. This works out to be about 600ml per hour. Spillage is also a big factor when planning fluid intake compared to actual intake during the race.

Sodium Intake

Sodium replacement is essential for endurance events. Replacement of between 0.25g per hour for those athletes who are susceptible to cramps, or 0.5g per liter of fluid for exercise activities lasting greater than one hour. Gastrolyte or a similar electrolyte replacement product you can buy from most pharmacies (drug stores). When it is made up to packet directions (one sachet for 200ml of water), it will provide this amount of sodium for 100mls. Check the label.

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