Carbohydrates have been unfairly demonised in diet and training literature. The reality is clear: for high-intensity performance, carbohydrates are irreplaceable.
Glycogen — The Performance Fuel
Glycogen is the stored form of glucose in the liver and muscles. The body can store roughly 400–500g of glycogen total (approx. 1,600–2,000 kcal). At intensities above ~65% of VO2max, glycogen is the dominant energy source — fatty acids oxidise too slowly to meet the energy demand at high intensity.
Depleted glycogen stores = “hitting the wall” (marathon) or “bonking” (cycling). This isn’t a gradual decline — it’s an abrupt performance collapse when the body is forced to reduce intensity to survive on fat and ketones.
Carbohydrate Timing
| Time | Recommendation | Reason |
|---|---|---|
| 2–3h pre-training | Low–medium GI (oats, sweet potato) | Stable energy throughout the session |
| 30–60 min pre-training | Medium GI, easily digested | Quickly available glucose without bloating |
| During training (>60 min) | 30–60g/h (gel, banana) | Prevents glycogen depletion |
| 0–30 min post-training | High GI (white rice, bread) + protein | Fast glycogen resynthesis, insulin spike |
Summary
Carbohydrates aren’t the enemy — they’re the tool. Right amount, right timing and right type of carbohydrates determines whether they support or sabotage your performance. Focus on fibre-dense, minimally processed sources like oats, sweet potato and rice — and time them intelligently around your training.
