Glycogen is a complex carbohydrate made of many glucose molecules linked together. Think of it as your body's rechargeable battery for exercise:
| Location | Storage Capacity | Function |
|---|
| Muscle glycogen | 300-500g | Powers muscle contractions |
| Liver glycogen | 80-120g | Maintains blood glucose |
| Total | ~400-600g | ~1,600-2,400 calories |
| Intensity | Primary Fuel |
|---|
| Rest/low intensity | Mostly fat |
| Zone 2 | Mix of fat and glycogen |
| Tempo/Threshold | Mostly glycogen |
| VO2 Max and above | Almost all glycogen |
The harder you work, the more glycogen you use.
| Exercise Time | Glycogen Status |
|---|
| 0-60 min | Adequate reserves |
| 60-90 min | Declining |
| 90-120 min | Critical levels |
| 120+ min (unfueled) | Depleted → bonking |
| What Happens | Result |
|---|
| Muscle glycogen depletes | Legs feel like lead |
| Liver glycogen depletes | Blood sugar drops |
| Brain glucose drops | Confusion, irritability |
| Overall | Bonking/hitting the wall |
Training teaches your body to use fat more efficiently, "sparing" glycogen:
| Adaptation | Result |
|---|
| More Zone 2 training | Better fat oxidation |
| Improved mitochondria | More efficient fuel use |
| Higher FTP | Higher intensity before glycogen dominates |
| Strategy | Effect |
|---|
| Carb loading | Increases stores 25-100% |
| Taper | Allows full replenishment |
| High-carb diet | Maintains full stores |
| State | Muscle Glycogen | Liver Glycogen | Total Calories |
|---|
| Normal | 300-400g | 80-100g | ~1,600 |
| After loading | 500-700g | 100-150g | ~2,600 |
That extra fuel can mean 30+ additional minutes of racing.
| Timing | Glycogen Synthesis Rate |
|---|
| First 2 hours post-exercise | 150% of normal |
| 2-6 hours | 100% |
| After 6 hours | 75% |
Key: Eat carbs within 2 hours post-exercise for fastest recovery.
| Timing | Carb Target |
|---|
| 0-30 min | 1g/kg body weight |
| Every 2 hours | 0.5g/kg |
| 24 hours | 8-10g/kg total |
| Food | Glycogen Replenishment |
|---|
| White rice | Excellent (fast) |
| Pasta | Excellent |
| Potatoes | Very good |
| Sports drinks | Good (immediate) |
| Fruit | Good |
| Whole grains | Good (slower) |
| Training State | Effect on Glycogen |
|---|
| Well-fueled | Full performance |
| Partially depleted | Reduced power output |
| "Train low" | Signals adaptation (use carefully) |
Some athletes occasionally train with low glycogen to enhance adaptation:
| Strategy | Purpose | Caution |
|---|
| Fasted morning ride | Improve fat oxidation | Keep intensity low |
| Depleted second session | Mitochondrial signals | Recovery crucial |
| Periodized nutrition | Strategic adaptation | Don't overuse |
Warning: Training low too often impairs performance and recovery.
| Distance | Glycogen Concern |
|---|
| 5K | Usually adequate |
| 10K | Usually adequate |
| Half marathon | May need fueling |
| Marathon | Critical—must fuel and load |
| Duration | Glycogen Concern |
|---|
| < 90 min | Usually adequate |
| 2-3 hours | Begin fueling at 60 min |
| 3+ hours | Continuous fueling essential |
| Distance | Glycogen Concern |
|---|
| Sprint | Usually adequate |
| Olympic | Some fueling needed |
| Half Ironman | Extensive fueling required |
| Ironman | Critical—600+ g carbs needed |
Signs include:
- Heavy legs
- Difficulty maintaining power/pace
- Mental fog or irritability
- Intense hunger
- Cold sweats
Can I train my body to store more glycogen?
Yes—endurance training increases glycogen storage capacity by 20-40%. Carb loading can temporarily increase stores by 25-100%.
No—glycogen is stored glucose (in muscles/liver), while blood sugar is glucose circulating in blood. Liver glycogen helps maintain blood sugar during exercise.
Yes—even fat-adapted athletes use glycogen for high-intensity efforts. Low-carb athletes may have reduced stores and impaired high-intensity performance.
