Why Carbohydrates Matter During Exercise
When you engage in moderate to high-intensity exercise, your body relies primarily on carbohydrates stored as glycogen in your muscles and liver for fuel. These glycogen stores are finite and can be depleted in as little as 60 to 90 minutes of strenuous activity. When stores run low, fatigue sets in, and your performance suffers. By consuming exogenous (external) carbohydrates during exercise, you provide a readily available fuel source, spare your internal glycogen reserves, and maintain high-intensity output for longer durations.
The Science Behind Intra-Workout Fueling
Carbohydrate consumption during exercise serves two main purposes:
- Maintains blood glucose: This prevents a drop in blood sugar (hypoglycemia), which can lead to fatigue and impaired cognitive function.
- Spares liver and muscle glycogen: By providing an external fuel source, the body relies less on its stored energy, allowing you to sustain your effort.
Additionally, research has shown that for shorter, high-intensity efforts, a simple carbohydrate mouth rinse can improve performance without ingestion. This is thought to stimulate receptors in the mouth that signal the brain, leading to a positive effect on motor output.
Carbohydrate Recommendations by Exercise Duration
The amount of carbohydrates you need per hour is directly correlated with the length of your workout. Here are the latest expert-backed recommendations based on exercise duration:
- For activities lasting 30-60 minutes: For shorter, high-intensity sessions, a small intake of 30g of carbohydrates per hour or even a carbohydrate mouth rinse is sufficient to provide a performance benefit. Pre-exercise meals are generally the main fuel source for these workouts.
- For activities lasting 1-2 hours: This is the range where mid-exercise fueling becomes crucial. Aim for 30-60g of carbohydrates per hour. This can be achieved with sports drinks, gels, chews, or even solid foods like a banana.
- For activities lasting 2-3 hours: The fueling requirements increase significantly. Target an intake of up to 60g of carbohydrates per hour. For higher intensities, this can be pushed towards 90g, especially if using multiple transportable carbohydrates.
- For activities lasting more than 2.5-3 hours (Ultra-endurance): For very prolonged efforts, the recommendation increases to 90g or more per hour. To maximize absorption and minimize gastrointestinal distress at these high rates, it is essential to use a combination of carbohydrate sources, such as glucose and fructose.
Multiple Transportable Carbohydrates
When consuming more than 60g of carbs per hour, your body's ability to absorb carbohydrates can be a limiting factor. The primary glucose transporter (SGLT1) can become saturated. However, by consuming a mix of glucose (or maltodextrin) and fructose, you can utilize different intestinal transporters (SGLT1 and GLUT5 respectively) simultaneously, allowing for higher absorption and oxidation rates of up to 90g or more per hour. The common ratio used is 2:1 (glucose:fructose).
Choosing Your Carbohydrate Source
The format of your carbohydrate intake is a matter of personal preference and practicality during your specific activity. Athletes often use a combination of drinks, gels, and solid foods. The key is to test your nutrition strategy during training to prevent issues on race day.
| Carbohydrate Source | Best For | Pros | Cons |
|---|---|---|---|
| Sports Drinks | Consistent, moderate-intensity efforts | Easy to digest, provides fluids and electrolytes | Can cause bloating if too concentrated |
| Gels | High-intensity efforts, rapid fuel delivery | Quick-absorbing, portable, and concentrated | Can cause gastrointestinal distress in large quantities |
| Chews/Blocks | Steady fueling, especially in team sports | Easy to carry and consume in small doses | May require chewing, which can be difficult during high intensity |
| Low-Fat Energy Bars | Longer, lower-intensity sessions | Offers a sense of satiety and solid food | Can feel heavy on the stomach, slower absorption |
| Real Foods (e.g., Banana) | Longer duration, less intense activities | Natural source of carbs and nutrients | Can be messy and harder to digest quickly |
Practical Tips for Fueling and Avoiding GI Distress
- Start Early and Consistently: Begin consuming carbohydrates within the first 15-20 minutes of prolonged exercise. Small, regular intakes are better tolerated than large, infrequent doses.
- Train Your Gut: Just like you train your muscles, you can train your gut to handle higher carbohydrate intake. Practice your fueling strategy during training sessions to increase the digestive system's absorptive capacity. This is crucial for adapting to the higher carb loads needed for ultra-endurance events.
- Stay Hydrated: Dehydration slows stomach emptying and can worsen gastrointestinal problems. Balance your carbohydrate intake with sufficient fluid intake, especially during hot conditions. Sports drinks containing electrolytes can help address both needs simultaneously.
- Don't Experiment on Race Day: Never try a new fueling product or strategy during a competition. All testing should be done during training to assess tolerance and effectiveness.
- Match Intensity to Intake: Adjust your carbohydrate intake to the intensity of your exercise. Lower-intensity efforts require less carbohydrate than higher-intensity efforts. For very low intensities, the body relies more on fat as fuel, and less carbohydrate is needed.
Conclusion
Optimizing your carbohydrate intake during exercise is a key strategy for maximizing performance, delaying fatigue, and ensuring a more positive training experience. For efforts under an hour, pre-exercise fuel is often sufficient, with a mouth rinse offering a small performance boost for high-intensity work. As exercise extends beyond 60 minutes, a systematic fueling strategy becomes vital. Target 30-60g of carbs per hour for workouts up to 2.5 hours, and push towards 90g per hour (using multiple transportable carbs) for longer, ultra-endurance events. The type of carb matters less than the amount, but finding a variety of sources that agree with your gut is essential. By practicing your fueling plan during training, you can build a robust nutrition strategy that supports your body's energy demands and helps you achieve your athletic goals.
For more detailed sports nutrition guidelines, including personalized strategies, consider consulting reliable sources such as the Gatorade Sports Science Institute.
