Beyond 120g/hr: How Pros REALLY Personalise Race Fuelling

The cycling world is obsessed with carbohydrates. For years, the mantra has been "more is better," with hourly intake recommendations climbing from 60g to 90g, and now settling at a formidable 120g/hr for many elite athletes. But what if that number, followed religiously by amateurs and pros alike, is wrong for you?

A groundbreaking new test, previously reserved for WorldTour teams, is now revealing the stark reality of individual fuelling needs. It demonstrates that our ability to use the carbohydrates we consume is highly personal. When combined with metabolic profiling tools like INSCYD, it allows riders to build a fuelling strategy with surgical precision, eliminating guesswork and maximising performance.

The Two Sides of the Fuelling Equation

For years, fuelling has been a one-sided conversation focused only on intake. However, a truly optimised strategy must answer two fundamental questions:

1. What is my body's actual carbohydrate demand at race intensity?

   
   

2. How much of the carbohydrate I consume can my body actually absorb and use?

   
   

Answering these questions moves an athlete from following generic advice to implementing a truly personalised and effective fuelling plan.

Part 1: Defining Your Need with INSCYD Testing

Before you can determine your intake, you must understand your output. This is where metabolic testing like INSCYD comes into play. Pro riders and coaches use INSCYD to create a complete metabolic profile of an athlete. It measures key metrics like your aerobic capacity (VO2​max), your glycolytic power (VL​Amax​), and, most importantly for fuelling, your exact fat and carbohydrate combustion rates at any given power output.

An INSCYD test will tell you precisely how many grams of carbohydrate your body is burning per hour to maintain your target race pace. For example, a rider's profile might show that at their marathon MTB race pace, they burn 130 grams of carbohydrates per hour.

This number is the athlete's total fuel demand. This is the non-negotiable amount of carbohydrate their muscles require each hour. Now, the question becomes: how do we best meet that demand?

Part 2: Measuring Your Capacity with Exogenous Oxidation Testing

This is where the new test, developed by sports scientists like Dr. Jamie Pugh at Liverpool John Moores University, changes the game. It directly measures your exogenous carbohydrate oxidation rate—the maximum amount of carbohydrates from drinks and gels that your body can effectively absorb, transport, and use for energy.

How the Test Works:

The test is non-invasive and can be done at home. After a brief period of dietary control, the athlete rides on a smart trainer at a steady, low intensity for 90 minutes. Every 15 minutes, they consume a specific drink mix.

This isn't just any energy drink. The carbohydrates in the mix are formulated with a Carbon-13 (13C) isotope. Naturally, almost all carbon is Carbon-12 (12C). By "tagging" the drink with the heavier 13C isotope, scientists can track it. When your body oxidises (burns) these specific carbohydrates for fuel, the 13C shows up in the carbon dioxide (CO2​) you exhale. By collecting breath samples, a lab can determine exactly what percentage of your energy came from the drink mix versus your body's internal stores.

The results are astonishingly personal. Dr. Sam Impey, a nutritionist who has worked with teams like Jayco-Alula, found his own oxidation rate was just 69 g/hr, despite being able to comfortably tolerate 120 g/hr during training. Meanwhile, recent tests on unnamed WorldTour pros have shown confirmed oxidation rates of over 180 g per hour. My own test revealed a capacity of 89 g per hour.

This reveals the critical flaw in the one-size-fits-all approach.

The Pro Strategy: Combining INSCYD and Oxidation Data

Here is how a WorldTour-level nutrition strategy is built using both sets of data:

1. Establish Demand (INSCYD): The INSCYD test shows the rider burns 130 g of carbs per hour at their goal race pace.

   
   

2. Establish Capacity (Oxidation Test): The 13C breath test shows the rider has a maximum exogenous oxidation rate of 95 g of carbs per hour.

   
   

3. Develop the Strategy: The rider now knows that to perform optimally, they must fuel with 95 g of carbs per hour. Any more than this won't be used for energy and could cause GI distress or is simply wasted weight and money.

   
   

4. Manage the Deficit: The rider also knows there is a 35 g/hr deficit (130g demand - 95g intake) that must be supplied by their internal glycogen stores. This allows them to calculate exactly how long they can maintain their race pace before their stores run critically low, enabling them to pace perfectly and avoid the dreaded bonk.

Why This Matters for Every Athlete

This level of precision isn't just for the pros. Understanding your personal numbers has huge implications:

• Preventing GI Distress: If you consume 120 g/hr but can only oxidise 80 g/hr, that excess 40g per hour is sloshing around in your gut, pulling in water and leading to the cramps and stomach issues that end races.

  
  

• Saving Money and Weight: Why carry and consume 12 gels for a 4-hour ride if your body can only actually use 8?

  
  

• Better Body Composition: For athletes managing their weight, understanding that the extra 30-40 g of sugar per hour they were consuming wasn't even contributing to performance is a revelation. As Dr. Impey put it, referring to the surplus carbs he was consuming, "those are the calories I can't afford to have."

The Future is Personal

This new frontier of nutrition science is just beginning. We are now asking deeper questions:

• Is oxidation rate trainable? Can a "gut training" protocol measurably increase your number, or are we just training our tolerance for discomfort?

  
  

• Is the 1:0.8 glucose-to-fructose ratio optimal for everyone? Or is this ratio also individual?

  
  

• Is there a genetic component? Do elite athletes possess a genetic advantage for carbohydrate absorption?

  
  

What is clear is that the era of generic fuelling advice is over. By first understanding your body's energy demands with a metabolic profile from INSCYD, and then defining your absorption capacity with exogenous oxidation testing, you can finally build a fuelling strategy that is truly your own.

Further Reading: Exogenous carbohydrate and regulation of muscle carbohydrate utilisation during exercise

s00421-021-04609-4.pdf

Download PDF • 1.20MB

Effect of carbohydrate–protein supplementation on endurance training adaptations

s00421-020-04450-1.pdf

Download PDF • 1.82MB