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If you suddenly experience a slump in performance during a sporting activity, a lack of carbohydrates is usually responsible. How can you prevent this from happening?

Do you know the feeling? You’re running or cycling for two or three hours, and suddenly, from one moment to the next, you feel completely drained and weak, as if someone pulled the plug?

This is usually because your body has used up its entire carbohydrate reserves, causing a sharp drop in your blood sugar levels. If this happens in the office, it’s not a big deal. But if it happens during exercise, it can lead to a sudden drop in performance, lack of strength, motivation loss, dizziness, and general discomfort.

No need for nutrition during the first hour

If you’re jogging or exercising for just one hour, you don’t need a specific nutrition strategy, nor any food or fluids during the activity. From one hour onward, however, you should start hydrating—ideally not just with plain water, but with a sports drink that contains carbohydrates. Unlike sugary soft drinks, which often contain around 12% carbohydrates, sports drinks typically contain only about 6%. This concentration ensures quick absorption by the body, which is why diluted apple juice (1:1, from 12% to 6%) is also a popular choice among athletes.

To make your carbohydrate stores last as long as possible during extended efforts, they should be well filled in advance through so-called carbo-loading. Additionally, during long sessions, carbohydrates (solid or liquid) should be consumed regularly, and the intensity of the activity should be adjusted. The higher the intensity, the faster the carbohydrate stores are depleted.

How many carbohydrates are really needed?

Depending on the duration and intensity of the activity, the following guidelines apply for carbohydrate intake during exercise:

• For 60–90 minutes: 30–45 g of carbohydrates per hour, e.g., one energy gel or 500 ml of sports drink
• For 90–150 minutes: 45–60 g of carbohydrates per hour, ideally combined (gels, bars, drinks)
• For more than 150 minutes: 60–90 g of carbohydrates per hour
• Elite athletes with a trained digestive system can even absorb up to 90–120 g per hour, provided they use a glucose-to-fructose mix (approx. 2:1 ratio), as found in modern sports drinks or gels.

Important: Energy intake should be practiced during training. The so-called "train the gut" principle helps you tolerate larger amounts without stomach problems. If you react too late or consume too little, you risk a performance crash.

What to do in case of an energy crash?

If you hit the wall despite all precautions, quickly digestible carbohydrates can help get you back on your feet. For example, energy gels, glucose tablets, or even plain sugar cubes—anything sweet will do! In an emergency, a nut croissant, doughnut or chocolate bar from the next bakery can also do the trick.

The advantage of sports drinks and gels is that they contain a variety of carbohydrates. This allows your body to absorb energy in stages (both short- and long-chain carbs), helping prevent a sudden drop in blood sugar. While pure glucose can help bridge an energy dip, your blood sugar will soon drop again unless you keep refueling.