Endurance 101 - Week 4 - FUELLING 101

Carbohydrate Fuelling for Endurance Sports: How to Calculate Your Needs & Why Electrolytes Alone Won’t Cut It

Whether you’re running a marathon, cycling for hours, or tackling a long-distance triathlon, fuelling strategy can make or break your performance. Many athletes focus on hydration and electrolytes, but for workouts lasting over an hour, carbohydrates are the real game-changer.

In this article, we’ll cover:

• Why carbohydrates are essential during endurance efforts

• How to calculate exactly how much carbohydrate you need

• Why electrolytes alone can’t sustain you beyond 60 minutes

• Quick-acting carbohydrate sources — from gels to “real food”

• An expanded race-day fuelling table with real-food options
  

Why Carbohydrates Are the Star of the Show

Your body runs on two primary fuels during exercise:

1. Carbohydrates — stored as glycogen in your muscles and liver

2. Fat — stored in much larger amounts throughout the body
   

While fat can provide energy for hours, it’s a slow-burning fuel that requires more oxygen to metabolize. At higher intensities — such as racing, climbing hills, or pushing pace — your muscles overwhelmingly prefer carbohydrates because:

• Carbs produce ATP (energy) quickly

• They require less oxygen per unit of energy produced

• They sustain high-intensity performance without forcing you to slow down
  

A well-fuelled athlete stores about 1,500–2,000 kcal of glycogen — enough for 90–120 minutes of moderate-to-hard effort. Once glycogen drops too low, your brain and muscles essentially “power down,” causing the bonk (also called “hitting the wall”).

Why Electrolytes Alone Aren’t Enough

Electrolytes — sodium, potassium, magnesium, calcium — are critical for:

• Nerve signalling

• Muscle contraction

• Hydration and fluid balance

However, electrolytes don’t provide energy. They’re like the engine oil in your car — vital for function, but useless if there’s no fuel in the tank.

During short, easy sessions (<60 min), water + electrolytes are often enough. But for anything over an hour, especially at race pace or higher intensity, carbohydrates are necessary to:

• Keep blood glucose stable

• Delay glycogen depletion

• Maintain mental sharpness

• Reduce perceived effort and muscle fatigue
  

How to Calculate Your Carbohydrate Needs

Sports nutrition expert Asker Jeukendrup (2014) recommends:

• 1–2.5 hours: 30–60 g carbs/hour

• 2.5+ hours: 60–90 g carbs/hour (using a mix of glucose + fructose for better absorption)

1 g carbohydrate = ~4 kcal

Example for a 4-hour marathon:

• Target: 60 g/hour × 4 hours = 240 g total carbs

• Calories: 240 g × 4 kcal = 960 kcal from carbs
  

If aiming for 60 g/hour, that’s:

• 2 gels per hour, or

• 1 gel + 1 small banana per hour, or

• 1 sports drink bottle + 2 dates per hour

• 10-15 Jelly babies/Sweets plus water per hour
  

Quick-Acting Carbohydrate Sources During exercise, digestion slows, so simple carbs are best. These can come from:

Sports Nutrition Products and normal food and sweets.

(Examples not limited to these only - READ your chosen brand label! )

• Gels: Maurten, GU, SIS, Huma, Honey Stinger, GI32, USN, Biogen etc (20–25 g carbs each)

• Chews/Gummies: Clif Bloks, Skratch, Honey Stinger, GI32, Racefood, USN and Biogen nougat (~8–10 g per piece)

• Sports Drinks: Tailwind, Maurten Drink Mix, Gatorade Endurance, GI32, USN, Biogen, Nuun etc (30–40 g carbs/bottle)

• Energy Waffles: Honey Stinger, GU Stroopwafel (~21 g carbs each)

  
  

Don't like gels and sugary Gu type fuels?- here are some real food options that work well. Nutritional gels although easy to use can be expensive especially if you have to use 6-8 on a marathon or long run weekend after weekend - Why not try some of these day to day food types that packs the same amount of Carbohydrates and are part of your weekly grocery shop.

Real-Food Options:

• Boiled baby potatoes (30 g carbs per 100 g) — sprinkle salt for electrolytes

• Rice cakes with honey/jam (~30–35 g carbs each)

• Bananas (~25 g carbs) — easy to digest and portable

• Dried fruit:

  • Dates (~6 g carbs each)

  • Figs (~5 g each)

  • Apricots (~4 g each)

• White bread with jam/honey (~20–25 g per slice)

• Small pancakes with syrup (~20–25 g each)

• Homemade energy balls with oats, honey, and dried fruit (~20 g each)

• Jelly sweets (Haribo, jelly babies — ~5–7 g each)
  

Real food works especially well in long races or training sessions where palate fatigue from gels becomes an issue.

Race-Day Fuelling Table

Duration	Carbs/hr Target	Sports Nutrition Examples	Real Food Examples
1.5–2 hrs	30–45 g	1 gel at 30 min, 1 gel at 60 min, optional gel at 90 min	½ banana + 2 dates per hour, or 4–5 jelly babies + water
3–4.5 hrs	50–70 g	1 gel every 30–35 min (6–8 total) + sports drink	Alternate: 1 gel + ½ banana every 30–40 min, or boiled potato with salt every 45 min
5+ hrs	60–90 g	Mix gels, chews, and sports drink every 20–30 min	Alternate between small rice cakes with honey, dates, bananas, small pancakes with syrup, boiled potatoes with salt, and dried figs

Notes for using real food:

• Cut into small bite-sized pieces for easier chewing and faster digestion

• Pair starchy foods with a sip of sports drink for faster absorption

• Practice in training — GI tolerance varies per person
  

How to Calculate Electrolyte Needs

Electrolyte requirements depend on:

• Sweat rate (how much you lose per hour)

• Sweat sodium concentration (varies 400–2,000 mg/L)

• Environmental conditions (heat, humidity)

General sodium guidelines:

• Moderate temps: 300–600 mg sodium/hour

• Hot conditions: 600–1,000 mg sodium/hour

Other electrolytes (potassium, magnesium, calcium) are important but typically lost in much smaller amounts compared to sodium and are often covered by sports drinks or electrolyte tablets. Race-Day Electrolyte Table

Duration	Sodium/hr Target*	Sports Nutrition Examples	Real Food/Other Options
1.5–2 hrs	300–500 mg	500 ml sports drink (300–400 mg sodium), 1 electrolyte tab	Salted banana chips (~150 mg) + small sports drink
3–4.5 hrs	500–800 mg	500–750 ml sports drink/hour, electrolyte capsule every 45–60 min	Boiled potatoes with salt, salted pretzels
5+ hrs	600–1,000 mg	Electrolyte capsules every 30–45 min, sports drink, salted gels	Salted mashed potatoes, broth, salted crackers

*Sodium targets vary by sweat rate and conditions — test in training for accuracy.

Putting It All Together

For endurance events and long training sessions:

1. Hydrate with water + electrolytes — don’t wait until thirsty

2. Fuel with 30–90 g carbs/hour — duration and intensity dependent

3. Mix sports nutrition and real foods to reduce flavour fatigue

4. Practice your fuelling plan in training — race day is not the time for surprises

5. Adjust above Nutrition to your Running pace - if you run for 3 hours use the 3 hour strategy
   

Carbs are the high-octane fuel your body craves when you’re pushing limits. Hydration keeps you from overheating, electrolytes keep your system firing, but without carbohydrates, you’ll stall before the finish line.

References:

• Jeukendrup, A. E. (2014). "A step towards personalized sports nutrition: carbohydrate intake during exercise." Sports Medicine, 44(S1), 25–33.

• Cermak, N. M., & van Loon, L. J. (2013). "The use of carbohydrates during exercise as an ergogenic aid." Sports Medicine, 43(11), 1139–1155.