Nutrition for Ultra-Endurance Sports: Calculating Hourly Energy Needs

“Athletes who eat well are the ones who go far” — in the world of ultra-endurance sports, this is not just a slogan, but a core principle that determines success or failure. Many athletes collapse in the final tens of kilometers, and the cause is often not insufficient fitness but a failed fueling strategy. This article will help you build a systematic ultra-endurance fueling plan.

Basic Energy Expenditure Calculations

Estimating Hourly Calorie Burn

Hourly energy expenditure at different exercise intensities (using a 70kg athlete as an example):

The human body cannot fully replace what it burns through food intake, but with appropriate fueling, the “energy deficit” can be kept within an acceptable range.

The Central Role of Carbohydrates

Carbohydrates are the most important fuel for endurance sports, for the following reasons:

1. Fast energy production: Compared to fat, carbohydrates oxidize about 3 times faster
2. Support high-intensity output: Fat cannot sustain output above roughly 65% of max heart rate
3. Maintain brain function: The brain needs about 5-6g of glucose per hour, and a drop in blood sugar directly impairs decision-making and willpower

Hourly Fueling Targets

Carbohydrate Intake

Recommendations from contemporary sports nutrition science:

• 1-2 hour exercise: 30-60g of carbohydrate per hour
• 2-3 hour exercise: 60-90g of carbohydrate per hour
• Ultra-endurance beyond 3 hours: 60-120g of carbohydrate per hour (after gut training)

The importance of a glucose + fructose mix: The human intestine absorbs glucose and fructose using different transporter proteins (SGLT1 vs. GLUT5). Combining the two can break through the single-sugar absorption ceiling of about 60g/hr, reaching 90g/hr or even higher.

Recommended ratio: glucose : fructose = 2:1 (e.g., maltodextrin + fructose)

Comparison of Common Ultra-Endurance Fueling Foods

Practical advice: Don’t rely on energy gels alone — prolonged reliance on gels can easily cause GI distress. The longer the event, the more you should increase the proportion of “real food.”

Fluid and Electrolyte Management

Hydration Strategy

Dehydration is one of the most common causes of impaired performance in ultra-endurance events, but overhydration (hyponatremia) is equally dangerous.

Science-based hydration: Use thirst as the primary signal to drink (Drink to Thirst) rather than mechanically drinking every 30 minutes. Studies show that athletes who drink according to thirst maintain more stable sodium levels and perform better at the finish.

Sodium Replenishment

During prolonged exercise, sweating carries away large amounts of sodium. The importance of sodium:

• Maintains normal muscle contraction: Low sodium can cause muscle cramps
• Maintains nerve conduction: Low sodium can cause dizziness and confusion
• Maintains osmotic balance: Prevents cellular swelling

It is recommended to replenish 500-1000mg of sodium per hour (adjusted for sweat rate and temperature), obtained through salt tablets, salty foods, or electrolyte drinks.

Gut Training: Not to Be Overlooked

Many athletes’ guts cannot absorb large amounts of fuel during a race — but this can be improved through training:

1. Train the gut alongside training: Follow your race-day fueling plan during long training sessions; don’t try new fueling products for the first time on race day
2. Gradually increase intake: Start at 60g per hour and gradually train up to 90g or more
3. Practice in heat: High temperatures slow gastric emptying, so adapt in advance
4. Avoid high-fiber foods: Reduce dietary fiber intake 24-48 hours before the race

Fueling Adjustments for Special Situations

Nighttime Fueling

Energy expenditure decreases at night, but the psychological need to eat becomes more frequent:

• Choose easy-to-digest warm foods (such as noodle soup, hot cocoa)
• Caffeine intake (coffee, caffeinated gels) is most effective late at night
• Avoid greasy and high-protein foods, which empty from the stomach slowly and can cause discomfort

Fueling in Cold Environments

Cold temperatures can mask the sensation of dehydration, making it easier to forget to fuel:

• Set reminders to eat and drink
• Warm beverages help maintain core body temperature
• Increase the proportion of carbohydrates to provide heat

Conclusion

There is no one-size-fits-all formula for ultra-endurance fueling strategy — it requires continuous experimentation and adjustment during training to find the fueling combination best suited to your own gut and body. Establish your “fueling script” before the race, and rehearse it repeatedly during training. Remember: fueling is a skill, and skills require practice.

Related Reading

• Fueling Strategy for Long-Distance Riding: How Many Carbs Per Hour?
• Ultra-Marathon Fueling Calculations: Personalizing Hourly Carbohydrate Grams and Fluid Intake
• Carbohydrate Strategy for Long-Distance Cycling: Hourly Intake and Digestion
• Ultra-Marathon Nutrition Strategy: A Complete Fueling Plan From Training to Race Day