How long of a run requires fuel? The endurance athlete's guide

Approximately 60 to 75 minutes of continuous, vigorous exercise can deplete your body's readily available glycogen stores. Understanding how long of a run requires fuel is crucial for endurance athletes seeking to maximize performance and avoid fatigue, often known as 'hitting the wall'.

Quick Summary

Fuelling is generally necessary for runs exceeding 60-75 minutes to replenish carbohydrate stores, maintain energy levels, and enhance performance and recovery.

Key Points

• 75-Minute Threshold: For most runners, mid-run fueling becomes necessary for efforts lasting longer than 75 minutes to prevent glycogen depletion.

• Carbohydrate Targets: Aim for 30-60 grams of carbohydrates per hour for runs over 75 minutes, increasing to 60-90 grams for runs exceeding 2.5 hours.

• Early and Often: Start fueling around 30-45 minutes into your run and take small, consistent amounts every 15-20 minutes to avoid stomach upset.

• Train Your Gut: Practice your race-day fueling and hydration strategy during training to condition your digestive system and discover what works best for you.

• Electrolyte Replacement: Don't forget electrolytes, especially sodium, on long runs or in hot weather, as they are crucial for fluid balance and muscle function.

• Monitor Your Body: Pay attention to signs of underfueling like fatigue, weakness, or feeling dizzy, and adjust your intake as needed.

• Hydration is Key: Proper hydration is as important as fueling and should be planned in the days leading up to a long run.

The Science of Fuelling: Glycogen and the 75-Minute Rule

For any physical activity, your body primarily relies on glycogen, a form of stored glucose derived from carbohydrates, for energy. Your muscles and liver store this glycogen, which acts as a ready fuel source during exercise. For runs that last less than 60 to 75 minutes, your body typically has enough stored glycogen to power you through without needing to consume additional fuel during the run itself, provided you’ve eaten a well-balanced meal a few hours prior. However, once you push beyond this threshold, these glycogen reserves begin to run low, and performance can suffer significantly. This is why the 75-minute mark is often cited as the point where a fueling strategy becomes essential for sustained effort and to prevent the dreaded 'bonk' or 'wall'.

Fuelling Strategies by Run Duration

Runs Under 75 Minutes

For shorter or easy-paced runs, a pre-run meal or snack is usually sufficient. Focus on easily digestible carbohydrates and avoid high-fat or high-fiber foods that can cause gastrointestinal distress. A banana, a piece of toast with jam, or a small bowl of oatmeal 45-60 minutes before you head out is an excellent strategy. Hydration is still important, so sip water before and after your run, especially on warmer days, but mid-run fueling is generally unnecessary.

Runs 75 Minutes to 2.5 Hours

This is the zone where mid-run fueling becomes critical. The goal is to consume 30 to 60 grams of carbohydrates per hour to maintain blood sugar levels and spare your glycogen stores. It's best to start fueling early, around the 30-45 minute mark, and continue with small, regular intakes every 15-20 minutes. This prevents overwhelming your digestive system. Along with carbs, replacing electrolytes lost through sweat is also important, especially if you're a heavy sweater or it's hot outside.

Runs Over 2.5 Hours (Marathons and Ultras)

For longer endurance events, a more aggressive fueling strategy is required. Aim to consume 60 to 90 grams of carbohydrates per hour. Many elite athletes train their gut to handle even higher intakes. This can be achieved by using a combination of different carbohydrate sources (glucose and fructose) to maximize absorption. For these long efforts, you will likely need a mix of solid foods, gels, chews, and sports drinks to keep energy levels stable and stomach issues at bay. Consistent hydration with electrolytes is paramount throughout the entire run.

What to Use for Fuel

Fuel Type	Digestion Speed	Convenience	Carb Content	Best For	Notes
Energy Gels	Fast	Very high	20-30g per gel	Intense running, race day	Require water to aid absorption; some contain caffeine.
Energy Chews/Blocks	Fast-Medium	High	Varies (e.g., 20-30g per pack)	Steady running, easy to portion	Less messy than gels; similar carb delivery.
Sports Drinks	Fast	Medium (carried)	15-30g+ per serving	All runs >75 mins	Combines carbs, fluids, and electrolytes; can be bulky to carry.
Dried Fruit	Medium	High	High (e.g., raisins)	Steady-paced running	Provides natural sugars and potassium; can be hard on the stomach for some.
Bananas	Medium	Medium	20-30g per banana	Slower-paced running	Natural, easy to digest for most; bulkier to carry.

Train Your Gut to Fuel

The digestive system, like any other muscle, needs to be trained to tolerate the stress of exercising while consuming food and fluids. Introducing different fuel sources and timing strategies during your long training runs is essential. Do not wait until race day to experiment with a new gel or drink; practice what you plan to use during training to prevent unwelcome gastrointestinal issues. Gut training can reduce the risk of nausea, cramps, and bloating, making your runs more comfortable and your race day successful. As you increase the duration of your long runs, gradually increase your carbohydrate intake per hour to allow your stomach to adapt. For more detailed guidance, consulting with a registered dietitian specializing in sports nutrition is a valuable step.

Hydration is a Partner to Fueling

Adequate hydration is inseparable from an effective fueling strategy. Dehydration can exacerbate gastrointestinal issues and drastically impair performance. The recommended fluid intake varies based on individual sweat rate, intensity, and weather conditions, so paying attention to your thirst and urine color is key. On runs over 90 minutes, electrolytes become increasingly important to help the body retain fluid and maintain muscle function. Many sports drinks and gels include electrolytes, but sometimes supplementation with a tablet or capsule is necessary. Remember to hydrate well in the days leading up to a long effort, not just on the morning of your run.

Conclusion: Fuel Your Body for Peak Performance

For most runners, the critical threshold for introducing mid-run fuel is between 60 and 75 minutes. Shorter runs can typically be handled by pre-run carbohydrates, but endurance efforts beyond that require a thoughtful, practiced strategy. By understanding the role of glycogen, experimenting with different fuel sources, and focusing on proper hydration and electrolyte replacement, you can prevent hitting the wall and unlock your full potential as an endurance athlete. Always listen to your body and train your gut to ensure a smooth, powerful performance when it matters most. You can explore more resources on running nutrition from the Mayo Clinic Health System.

Keypoints

• 75-Minute Threshold: For most runners, mid-run fueling becomes necessary for efforts lasting longer than 75 minutes to prevent glycogen depletion.
• Carbohydrate Targets: Aim for 30-60 grams of carbohydrates per hour for runs over 75 minutes, increasing to 60-90 grams for runs exceeding 2.5 hours.
• Early and Often: Start fueling around 30-45 minutes into your run and take small, consistent amounts every 15-20 minutes to avoid stomach upset.
• Train Your Gut: Practice your race-day fueling and hydration strategy during training to condition your digestive system and discover what works best for you.
• Electrolyte Replacement: Don't forget electrolytes, especially sodium, on long runs or in hot weather, as they are crucial for fluid balance and muscle function.
• Monitor Your Body: Pay attention to signs of underfueling like fatigue, weakness, or feeling dizzy, and adjust your intake as needed.

Faqs

• How do I know if I need to fuel during a run? You likely need to start fueling if your run exceeds 75 minutes. Signs that you are under-fueled include a sudden drop in energy, heavy legs, or hitting a mental 'wall'.
• What are glycogen stores? Glycogen is the form of stored glucose (sugar) that your body uses for energy, primarily stored in your muscles and liver. It is the main fuel source for moderate-to-high intensity running.
• Can I run on an empty stomach? Yes, for shorter, easy runs (under 60 minutes). However, for more intense or longer runs, eating some simple carbohydrates beforehand is recommended to maintain energy and prevent fatigue.
• Should I use gels or real food? This depends on personal preference and what your gut can tolerate. Energy gels are convenient and fast-digesting, while some runners prefer easily digestible real foods like bananas or dried fruit. It is crucial to test both during training.
• Do I need electrolytes? Yes, for runs over 90 minutes or in hot conditions. You lose electrolytes like sodium through sweat, and replacing them helps maintain proper hydration and muscle function.
• What is 'hitting the wall'? Hitting the wall, or 'bonking', is the point of exhaustion that occurs when your body completely depletes its glycogen stores. It leads to a dramatic drop in performance and a feeling of extreme fatigue.
• What should I eat before a long run? Eat a carbohydrate-rich meal (e.g., oatmeal, bagel, pasta) 1-4 hours before your run to top off your glycogen stores. Keep fat and fiber low to minimize the risk of stomach issues.

Citations

• OutsideOnline: How to Fuel Long Runs with Real Food - https://run.outsideonline.com/nutrition-and-health/training-nutrition/how-to-fuel-long-runs-with-real-food/
• STYRKR: What to eat during a long run | STYRKR - https://styrkr.com/blogs/training-and-nutrition-hub/what-to-eat-during-a-long-run
• The Mother Runners: Marathon Fueling 101: What to Eat Before, During, & After Running - https://www.themotherrunners.com/marathon-fueling-101-what-should-runners-eat/
• Runner's World: Fuelling for a marathon: A runner’s guide to getting it right - https://www.runnersworld.com/uk/nutrition/diet/a776033/how-to-fuel-your-body-best-during-marathon-training/
• Johns Hopkins Medicine: Runner's Diet - https://www.hopkinsmedicine.org/health/wellness-and-prevention/runners-diet
• Mayo Clinic Health System: Fueling your run with good nutrition - https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/fueling-your-run-with-good-nutrition
• Saga: How to fuel long runs so you feel good all the way to the end - https://www.saga.co.uk/magazine/health-and-wellbeing/how-to-fuel-long-runs

Frequently Asked Questions

How do I know if I need to fuel during a run?

You likely need to start fueling if your run exceeds 75 minutes. Signs that you are under-fueled include a sudden drop in energy, heavy legs, or hitting a mental 'wall'.

What are glycogen stores?

Glycogen is the form of stored glucose (sugar) that your body uses for energy, primarily stored in your muscles and liver. It is the main fuel source for moderate-to-high intensity running.

Can I run on an empty stomach?

Yes, for shorter, easy runs (under 60 minutes). However, for more intense or longer runs, eating some simple carbohydrates beforehand is recommended to maintain energy and prevent fatigue.

Should I use gels or real food?

This depends on personal preference and what your gut can tolerate. Energy gels are convenient and fast-digesting, while some runners prefer easily digestible real foods like bananas or dried fruit. It is crucial to test both during training.

Do I need electrolytes?

Yes, for runs over 90 minutes or in hot conditions. You lose electrolytes like sodium through sweat, and replacing them helps maintain proper hydration and muscle function.

What is 'hitting the wall'?

Hitting the wall, or 'bonking', is the point of exhaustion that occurs when your body completely depletes its glycogen stores. It leads to a dramatic drop in performance and a feeling of extreme fatigue.

What should I eat before a long run?

Eat a carbohydrate-rich meal (e.g., oatmeal, bagel, pasta) 1-4 hours before your run to top off your glycogen stores. Keep fat and fiber low to minimize the risk of stomach issues.