The Core Factors: Weight and Pace
Determining the number of calories you burn per hour during a marathon is not a one-size-fits-all calculation. The two most significant variables are your body weight and your running pace.
Heavier runners, by virtue of moving more mass over the distance, will expend more energy and burn more calories. For example, a 185-pound runner will burn more calories per hour than a 125-pound runner at the same pace. Similarly, the faster you run, the more energy your body demands per minute, leading to a higher hourly calorie burn rate. While faster runners complete the race in less time, their higher intensity often results in a higher rate of calorie expenditure during that shorter period.
Comparing Hourly Calorie Burn by Weight and Pace
| Weight (lbs) | 12 min/mile (5 mph) | 10 min/mile (6 mph) | 8 min/mile (7.5 mph) |
|---|---|---|---|
| 125 lbs | Approx. 480 kcal/hr | Approx. 560 kcal/hr | Approx. 680 kcal/hr |
| 155 lbs | Approx. 576 kcal/hr | Approx. 704 kcal/hr | Approx. 850 kcal/hr |
| 185 lbs | Approx. 672 kcal/hr | Approx. 840 kcal/hr | Approx. 1020 kcal/hr |
Note: These are approximations and can vary based on other factors.
Additional Factors That Influence Your Calorie Burn
Beyond weight and pace, several other elements contribute to your final energy expenditure. Taking these into account allows for a more personalized fuelling plan.
- Running Efficiency: Experienced runners with better form are often more efficient and may burn fewer calories per mile than novices.
- Terrain and Elevation: Running uphill or on uneven trails requires significantly more energy than running on a flat road.
- Weather Conditions: High temperatures and humidity force your body to work harder to regulate its temperature, increasing your overall calorie burn.
- Metabolic Rate: Each person has a unique base metabolic rate, which affects how they use energy. Wearable devices can offer personalized insights by tracking real-time data like heart rate.
The Paradox: Burn vs. Intake
It is a common misconception that you can or should replace all the calories you burn during a marathon. The reality is that your body burns calories at a far faster rate than it can digest and absorb them during intense exercise. A typical runner can only absorb about 200-300 calories per hour while racing. Your body relies on its stored glycogen and fat reserves to cover the deficit. This is why proper carbohydrate loading in the days leading up to the race is so critical.
How to Fuel Your Marathon
Since you cannot consume all the calories you burn, your fuelling strategy focuses on a consistent intake of carbohydrates to supplement your body's glycogen stores. It is essential to practice this strategy during your long training runs to train your gut and avoid stomach issues on race day.
Key Fuelling Recommendations
Experts recommend consuming between 30 and 90 grams of carbohydrates per hour, depending on your pace, training, and tolerance.
- First 1-2 hours: Aim for 30-60g of carbs per hour.
- After 2 hours: Experienced runners can increase intake to 60-90g per hour, especially if they have trained their gut to handle it.
Fueling Options:
- Energy Gels: Highly concentrated and easy to carry, though they must be consumed with water.
- Sports Drinks: Offer a combination of carbohydrates and electrolytes, simultaneously addressing hydration and fuelling needs.
- Energy Chews: Solid, chewable options that provide a steady stream of carbs.
- Whole Foods: Options like bananas or small pieces of a peanut butter sandwich, often favoured by ultrarunners.
For additional resources on marathon nutrition, visit reputable sources like Runner's World, who provide detailed guides on fuelling strategies.
Understanding Calorie Calculators and Wearables
Online calculators and modern GPS watches offer a convenient way to estimate your calorie burn. While not perfect, they provide a valuable baseline by incorporating factors like weight and pace into a calculation, sometimes using a concept called Metabolic Equivalent of Task (METs). More advanced wearables can use heart rate data and other metrics to give you a more accurate, real-time estimate of your energy expenditure. Regardless of the tool, remember to use these figures as a guide and always practice your nutrition strategy during training to see what works for your unique body.
Conclusion: Personalize Your Approach
In summary, the question of how many calories per hour during a marathon has no single answer, as individual burn rates depend on multiple factors, primarily weight and pace. While you may burn 600-1000 calories or more per hour, your body can only absorb a fraction of that during the race. Therefore, a consistent intake of 30-90 grams of carbohydrates per hour, based on your training and tolerance, is the key to maintaining energy levels and avoiding performance drops. By understanding your unique calorie needs and practicing your fuelling plan, you can successfully power your marathon effort from start to finish.
