Carbs Are King in CrossFit & HYROX—Here’s How to Use Them for Peak Performance

Carbohydrates are the primary fuel source for high-intensity sports like CrossFit and HYROX, where energy demands are extreme. Athletes who fail to optimize their carb intake risk hitting “the wall”—a rapid decline in performance caused by glycogen depletion.

According to Wod Science, “Carbs remain king when it comes to exercise performance.” Understanding how to fuel properly before and during workouts can make a significant difference in endurance, strength, and overall athletic output.

Why Carbohydrates Are Essential for High-Intensity Exercise

Carbohydrates provide the fastest and most efficient source of energy for working muscles. When exercise intensity increases, the body shifts away from burning fat and relies almost entirely on carbohydrates to generate ATP—the energy currency of the muscles.

Scientifically, carbohydrates are superior to fats in high-intensity exercise because they produce 15% more ATP per unit of oxygen. As Wod Science explains, “The efficiency of burning carbohydrates is much higher compared to fats, making them the preferred fuel when oxygen is limited.”

Glycogen Depletion and Its Impact on Performance

Glycogen, the stored form of carbohydrates, is limited in supply—with only about 500 grams stored in muscles and 100 grams in the liver. This equates to roughly 2,000 to 3,000 calories of energy, which can be rapidly depleted during intense exercise.

A 1993 study demonstrated how glycogen levels impact endurance. Athletes who began exercise with high glycogen stores and consumed carbohydrates during training performed significantly better than those who started with low glycogen levels. Those who failed to replenish glycogen mid-workout experienced sharp declines in power output after just 40-50 minutes.

Fueling Strategies for HYROX vs. CrossFit

While both HYROX and CrossFit depend on carbohydrate metabolism, their fueling needs differ due to variations in workout duration and intensity.

HYROX (Endurance-Based, 60-90+ Minutes)

Since HYROX events last well over an hour, athletes must ensure glycogen stores are full before competition and continue fueling during the race.

Recommended carbohydrate intake:

• Night before: 4g carbs per kg body weight (starches, grains, pasta).
• Breakfast (2-3 hours before): 2-4g carbs per kg (simple carbohydrates like toast, bananas, or oatmeal).
• During event: 60-90g carbs per hour (sports drinks, energy gels) to maintain energy levels.

Wod Science explains: “After 45-50 minutes without carbohydrate intake, performance starts to decline. If you’re training for HYROX, consuming carbs mid-race can help sustain intensity.”

CrossFit (Short, High-Intensity, 10-20 Minutes)

CrossFit workouts are brief but extremely demanding, relying heavily on glycogen. Unlike HYROX, carbohydrates are not needed during workouts, but pre-workout nutrition is crucial.

Recommended carbohydrate intake:

• Night before: 3-4g carbs per kg.
• Breakfast (2-3 hours before): 2-4g carbs per kg (fast-digesting carbs like rice cakes, fruit, or sports drinks).
• During workouts: No carbs needed (unless competing in multiple events, in which case 60-90g per hour between sessions is recommended).

Avoid Eating Carbs Right Before Exercise

A common mistake athletes make is consuming carbohydrates too close to workout time. This can trigger exercise-induced hypoglycemia, where blood sugar levels drop sharply after insulin spikes.

“Many people think drinking a Gatorade or eating a banana right before starting will boost energy, but this can actually cause dizziness and fatigue,” says Wod Science. Instead, carbohydrates should be fully digested before exercise to be stored as glycogen rather than lingering in the bloodstream.

Protein and Fat Considerations

• Limit protein before workouts: High protein intake before exercise can slow digestion and delay carbohydrate absorption.
• Minimize fat intake before exercise: Fats take longer to digest and should be reserved for post-workout meals.
• Prioritize protein after training: Helps with muscle recovery and glycogen replenishment.

Adjusting Carbohydrate Intake for Early Morning Training

For athletes training very early in the morning (5-7 AM), traditional breakfast timing isn’t feasible. Two strategies can help:

1. Skip breakfast if the previous night’s meal was high in carbs. Glycogen stores will still be sufficient for one or two workouts.
2. Adjust carb intake based on available time before training:
   • 4 hours before: 4g per kg
   • 3 hours before: 3g per kg
   • 2 hours before: 2g per kg
   • 1 hour before: 1g per kg
   • <1 hour before: Avoid high-carb intake to prevent blood sugar crashes.

Maximizing Carbohydrate Absorption: The Glucose-Fructose Strategy

Some athletes struggle to consume enough carbohydrates during competition due to gastrointestinal discomfort. Research shows that glucose transporters in the intestine max out at 60g per hour, but combining glucose with fructose allows for up to 90g per hour.

As Wod Science explains, “Fructose uses a different transporter than glucose, so combining them allows athletes to absorb more total carbohydrates without stomach issues.”

Conclusion: Smart Carbohydrate Strategies Enhance Performance

For high-intensity athletes, fueling correctly can mean the difference between peak performance and mid-workout fatigue. Understanding how to time and balance carbohydrate intake before, during, and after training ensures muscles have the energy they need to sustain power and endurance.

By following science-backed nutrition strategies, CrossFit and HYROX athletes can optimize performance, prevent energy crashes, and recover more effectively.