01 · The fuel of your musclesThe fuel of your muscles
Carbohydrates are the main engine of your body while running. As soon as you start exercising, your body first uses the glycogen stores in your muscles and liver. That glycogen is converted into glucose — the fastest and most efficient source of energy you can use during exercise. That's why workouts in which you start "full" often feel so much lighter and smoother.
If you have consumed too few carbohydrates, your glycogen stores will run out more quickly. Your blood sugar levels drop, your stride feels heavy and your pace plummets. That recognizable moment is often called “the man with the hammer” among runners: you can no longer accelerate, even if you want to. It's not a lack of motivation, but simply a lack of available fuel.
During an easy endurance run, your body can use more fats — which is slow but efficient. But as soon as the intensity increases, for example during a tempo run, hill training or interval, your body switches almost completely to carbohydrates. Fats simply cannot be converted quickly enough for this type of effort.
Eating enough carbohydrates before and after your training not only helps you perform better, but also to recover well and replenish your glycogen stores.
02 · Before, during and after trainingBefore, during and after training
Before running
During running
After running
A good carbohydrate strategy is all about timing. Your body mainly burns glycogen (stored carbohydrates) while running, and the better you manage that supply, the more constant your energy and pace will remain. The approach differs before, during and after training — especially for longer distances or intense sessions.
Before running
The goal is to optimally fill your glycogen stores and gently prepare your body for exercise.
while running
For workouts longer than 75–90 minutes (or for intense sessions such as long tempo runs), it pays to replenish fuel along the way. This prevents a dip, keeps your heart rate more stable and postpones fatigue.
After running
Recovery starts as soon as you stop running. Your body wants to replenish glycogen, repair muscles and reduce inflammation. The right nutrition within the first half hour speeds up that process considerably.
This approach supports every phase of your training — from starting energy to steady pace and rapid recovery. This way you get more out of your sessions and arrive fitter for the next training every week.
03 · How much do you need?How much do you need?
Your carbohydrate needs depend greatly on the intensity and duration of your training. The faster or longer you run, the more glycogen your muscles use — and the more important it becomes to maintain those stores. The diagram below will help you make a realistic estimate:
For a 70 kg runner, that means 350–700 grams of carbohydrates on intense training days — more than many people expect. It shows how important nutrition is for performance and recovery.
04 · Carbohydrates and fat burning: contradictory?Carbohydrates and fat burning: contradictory?
It seems like eating carbohydrates and stimulating fat burning are mutually exclusive, but in reality they reinforce each other when you time it right.
During gentle endurance running (zone 1–2), your body uses relatively many fats as an energy source. A moderate carbohydrate intake can help: you learn to use fats more efficiently without having to increase your intensity.
But as soon as your pace increases — think tempo runs, hills, intervals or races — your body runs almost entirely on carbs. Fat burning simply cannot provide energy fast enough for higher speeds.
Therefore, the idea that “fewer carbs is better for fat burning” is only partly true:
A chronic carbohydrate deficiency:
So the key is balance: Use gentle workouts to train your fat burning, but support your heavy sessions and total weekly load with sufficient carbohydrates. This way you build up both endurance and speed, without sacrificing recovery or health.