Glycogen: Your Hidden Fuel Tank Explained
Your muscles hold enough glycogen for 90–120 minutes of racing. Learn how to maximize these stores and use them efficiently for better endurance performance.
Quick Answer
Glycogen is your muscles' primary fuel, storing 400–500 grams (1,600–2,000 calories) that last 90–120 minutes at race pace. Carb loading maximizes stores; during exercise, consuming 60–90 g carbs/hour extends your fuel supply.
You train for months. You taper. You arrive at the start line ready to race.
But there's something working against you that you can't see: your glycogen stores.
Glycogen is your muscles' primary fuel — and there's not nearly as much of it as you'd think.
What Is Glycogen?
Glycogen is the stored form of carbohydrates in your body. Think of it as starch stored in your muscles and liver.
When you eat carbs, your body breaks them down into glucose. Some glucose is used immediately for energy; the rest is stored as glycogen for later use.
How Much Glycogen Do You Have?
| Feature | Storage Location | Amount | Purpose |
|---|---|---|---|
| Muscle glycogen | 400–500 g (1,600–2,000 cal) | Primary fuel for exercise | |
| Liver glycogen | ~100 g (400 cal) | Maintains blood sugar | |
| Total usable | ~2,400 calories | Extended moderate effort |
How Long Does Glycogen Last?
At rest, you burn mostly fat. At race pace, you burn mostly carbohydrates.
Your 400–500 grams of muscle glycogen will last approximately 90–120 minutes at marathon pace. Once it's gone, you hit the wall.
Maximizing Your Glycogen Stores
Carb loading can increase glycogen stores by 50–100%:
- Begin 2–3 days before your race
- Reduce training volume while increasing carb intake
- Target 8–10 g carbs per kg body weight daily
- Choose low-fiber, easily digested carb sources
- Stay hydrated — glycogen binds with water
Extending Your Fuel During Exercise
Even with full glycogen stores, you'll deplete them during long efforts. Consuming carbs during exercise extends your fuel supply.
- Start consuming carbs within 30 minutes of starting
- Aim for 60–90 g carbs per hour (with training)
- Use gels, drinks, or solid foods depending on gut tolerance
- Combine with hydration for optimal absorption
Glycogen Replenishment After Training
After training, you need to replenish glycogen for your next session:
- Consume 1.0–1.2 g carbs per kg within 60 minutes
- Include protein to enhance glycogen synthesis
- Continue carb intake with meals over the next 24 hours
- Full replenishment takes 24–48 hours with adequate intake
What Happens When Glycogen Runs Out?
When glycogen depletes:
- Blood sugar drops, causing mental fog
- Muscles lose their primary fuel source
- Pace collapses dramatically
- Recovery takes longer
Optimize your glycogen strategy with AI-powered guidance.
Download MAVRFrequently Asked Questions (FAQ)
Can I increase my glycogen capacity?
Yes, through carb loading and training. Regular high-carb training increases your muscles' ability to store and use glycogen.
Why do I still hit the wall even after carb loading?
Carb loading extends your fuel supply, but you still need to consume carbs during the race to go beyond the 90–120 minute mark.
What foods are best for glycogen replenishment?
High-glycemic carbs like white rice, pasta, potatoes, sports drinks, and fruit juices replenish glycogen quickly.
Does fat adaptation affect glycogen use?
Fat adaptation can improve your ability to burn fat, but you still need glycogen for high-intensity efforts. It doesn't eliminate the need for carb fueling.