Glycogen: Your Body Primary Training Fuel and How to Manage It
Glycogen - the stored form of carbohydrate in muscle and liver - is the primary fuel for moderate-to-high intensity exercise. Managing it intelligently changes training performance and recovery.
What Glycogen Is
Glycogen is glucose stored in branched chains in muscle cells and the liver. Muscle glycogen is the primary fuel for exercise at intensities above approximately 60-65% of VO2 max. Liver glycogen maintains blood glucose between meals and supplies the brain. Together they store approximately 400-500g of glycogen (1,600-2,000 kcal) in a 70kg person - enough for roughly 90-120 minutes of continuous moderate-high intensity exercise.
When Glycogen Matters Most
At low exercise intensities (Zone 1-2), the body can sustain work primarily from fat oxidation with minimal glycogen contribution. As intensity rises above Zone 2, the contribution of glycogen increases steeply. By Zone 4-5 (high-intensity intervals, tempo runs, CrossFit), glycogen is the dominant fuel. Starting these sessions with depleted glycogen directly impairs performance and increases perceived exertion.
"Carbohydrate is not the enemy of the athlete - glycogen depletion is. Understanding when to have carbohydrate available and when it matters less is fundamental sports nutrition." - Louise Burke, Australian Institute of Sport
Signs of Glycogen Depletion
- Sudden, severe fatigue mid-workout ("bonking" or "hitting the wall")
- Inability to sustain pace or effort that previously felt manageable
- Difficulty concentrating during or after prolonged exercise
- Persistent morning fatigue in athletes training frequently
Glycogen Restoration After Training
| Scenario | Carbohydrate strategy |
|---|---|
| Next training in 24+ hours | Normal carbohydrate intake with meals is sufficient |
| Next training in 8-24 hours | 1-1.2g/kg carbohydrate in first 4 hours post-training |
| Next training in under 8 hours | 1.2g/kg/hr for 4-6 hours; adding protein enhances resynthesis |
Glycogen Management in Practice
For the majority of moderate exercisers (3-5 sessions per week, under 60 minutes each), habitual whole food carbohydrate intake is sufficient - glycogen is fully replenished within 24 hours on a normal diet. Strategic glycogen management becomes important for athletes training twice daily or competing in multi-day events. For everyone else: eat carbohydrates with meals, prioritise fibre-rich sources, and ensure your carbohydrate intake is not chronically restricted below your training energy requirements.
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