Carb Loading for Hyrox: Does It Work, How Much, and the 48-Hour Protocol (Nutrition Series, Part 2)
Carb loading is real, but most people do it wrong. Here is whether Hyrox is long enough to benefit, the 48-hour protocol, the right amount to eat, and why the bloated feeling the day before is fine.
Does Hyrox last long enough to benefit from carb loading?
Yes — for almost every Open athlete. The relevant threshold is roughly 60–75 minutes of sustained high-intensity exercise. Below that, pre-existing glycogen stores are usually adequate. Above it, glycogen depletion is a measurable performance limiter.
Most Open Hyrox athletes race between 75 and 105 minutes. At race intensity (85–95% of max heart rate), glycogen burns at approximately 60–80g per hour. Your muscles and liver store roughly 400–500g of glycogen. At 90 minutes of maximal effort, you are approaching the bottom of that tank.
Carb loading for 48 hours before the race extends those stores to their maximum capacity — roughly 550–600g of glycogen in trained athletes. That is the difference between running out of fuel at station 6 and arriving at wall balls with enough left to push.
The full 5-part Nutrition for Hyrox Athletes series
New parts drop every 2nd day. Bookmark the Nutrition series hub to follow along.
- Part 1 — Race-Day Breakfast: What to Eat 3h, 2h, and 1h Before the Gun
- Part 2 — Carb Loading for Hyrox: Does It Work, How Much, and the 48-Hour Protocol (you are here)
- Part 3 — Hyrox Hydration Strategy: Electrolytes, Sweat Rate, and the On-Course Drink Plan
- Part 4 — Post-Race Recovery Nutrition: The 72-Hour Protocol After a Hyrox
- Part 5 — Daily Nutrition for Hyrox Training: Protein, Carbs, and Calorie Targets for Hybrid Athletes
The physiology of glycogen loading
Glycogen is glucose stored in muscle tissue and the liver. Each gram of glycogen binds approximately 3g of water — which is why carb loading causes weight gain and a bloated feeling (more on this below). When muscle glycogen is fully loaded, trained athletes can store 15–20g per kg of lean muscle mass, plus 80–100g in the liver.
The standard training diet keeps glycogen at 60–80% of maximum. A deliberate carb loading protocol pushes this to close to 100% over 48 hours. The physiological benefit is an extra 100–150g of glycogen available — equivalent to approximately 15–20 minutes of additional high-intensity performance before depletion.
For a race where glycogen depletion may occur in the final 20–30 minutes (stations 6–8), this matters.
What carb loading is not
It is not eating pasta the night before. A single pasta dinner the evening before a race barely shifts glycogen stores. One meal cannot undo weeks of normal carbohydrate intake. A proper carb load takes 48 hours.
It does not require a depletion phase. Older protocols involved 3–4 days of carbohydrate restriction to “deplete” glycogen before the loading phase. Modern research shows this is unnecessary for events under 90–120 minutes. Just load for 48 hours. No depletion needed.
It is not a calorie surplus. Carb loading replaces some dietary fat with carbohydrate. Total calories stay roughly similar — the composition changes, not necessarily the total.
The 48-hour protocol
Target carbohydrate intake
The loading dose is 8–10g of carbohydrate per kg of bodyweight per day for the 48 hours before the race.
For a 70 kg athlete: 560–700g carbohydrate per day. For an 80 kg athlete: 640–800g carbohydrate per day.
This is significantly more than a typical training diet (3–5g/kg/day for most recreational athletes). It requires deliberate meal planning.
Day 2 before the race (48 hours out)
Reduce training significantly or rest entirely. A short easy run (20–30 min) is fine to maintain muscle sensitivity to glycogen storage.
Sample meal plan for a 75 kg athlete targeting 600g carbohydrate:
Breakfast: Large bowl of oats (100g dry) with honey (30g) and banana. White toast (2 slices) with jam. Orange juice (250ml). = ~200g carbs
Mid-morning snack: Rice cakes (4) with honey. Banana. = ~70g carbs
Lunch: Large portion white rice (250g cooked) with grilled chicken and a small side salad (minimal dressing). Apple juice. = ~120g carbs
Afternoon snack: White bread roll with jam. Sports drink (500ml). = ~80g carbs
Dinner: Large pasta serving (100g dry weight, cooked) with a light tomato sauce and lean protein. Garlic bread (2 slices). = ~130g carbs
Total: approximately 600g carbohydrate
Day 1 before the race (24 hours out)
Same carbohydrate target. Same meal composition. Avoid high-fibre, high-fat, and anything unfamiliar.
Dinner the night before should be:
- Eaten 3–4 hours before bedtime (not immediately before sleep, which impairs digestion)
- High carbohydrate, moderate protein, very low fat and fibre
- Completely familiar food you have eaten before
Good options: pasta with tomato and lean protein, white rice with chicken and minimal fat, potato-based meals with lean protein.
Avoid: pizza, creamy sauces, high-fat meats, raw vegetables, beans and legumes, alcohol.
Managing the side effects
The bloat
Carb loading causes a noticeable bloated feeling and temporary weight gain of 1–3 kg. This is the glycogen-water binding — for every gram of glycogen stored, approximately 3g of water is retained.
This is normal. It is desirable. It is the fuel you need.
The weight gain is temporary and is composed entirely of water and glycogen — it does not represent fat gain. You will lose it during the race as you burn through the glycogen.
Some athletes find the bloated feeling uncomfortable and back off the carb load too early. Do not do this. Trust the physiology.
GI discomfort
The GI discomfort associated with carb loading is usually from eating too much fibre (high-fibre carb sources) or too much food volume at once. Solve both by:
- Using white/refined carbohydrate sources (white rice, white pasta, white bread, bananas, fruit juice, sports drinks)
- Spreading the carbohydrate intake across 5–6 meals and snacks rather than 3 large meals
Sleep quality
Some athletes sleep less well when they have eaten a very large dinner. This is a stomach-emptying issue, not a carb issue. Eat your final large meal 3–4 hours before bed and have only a small snack afterward if needed.
Alcohol
Do not drink alcohol in the 48 hours before the race. Alcohol:
- Impairs glycogen synthesis directly
- Disrupts sleep quality
- Causes dehydration
- Increases cortisol
Even one or two drinks the night before measurably impairs glycogen storage. The carb loading protocol requires these 48 hours to be clean.
Sub-70 min athletes: is it worth it?
If you are racing in under 70 minutes, the benefit of carb loading is smaller. Your glycogen stores are unlikely to be the limiting factor in a 60–65 minute race. A normal high-carbohydrate diet in the 24 hours before the race (4–5g/kg/day) is sufficient.
Full carb loading is most valuable for athletes racing 75 minutes or longer.
What’s next
Part 3 covers hydration — the electrolyte protocol, sweat rate management, and on-course drink strategy.
→ Part 3: Hyrox Hydration Strategy
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