The Science of Cycling

Cycling is a particularly analytic sport. The advent of power meters and heart rate monitoring enables athletes and coaches to quantify virtually everything that informs their training and nutrition strategies, and helps predict future performance. Power meters tell you how much mechanical power you put into each pedal stroke, which has a close relationship with how much total energy you’re burning.

In sports like running, it’s challenging to accurately measure mechanical power. This makes cycling the preferred exercise mode for scientists, as it allows for the measurement of everything, making it quite a mathematical endeavor.

Endurance Sport Nutrition

The longer an endurance event is, the more critical your fueling strategy becomes. The body has sufficient internal energy stores to sustain us through high-intensity events for approximately 90 minutes. However, once you start approaching 2+ hours, and in the case of ultra-type events, doing that multiple days in a row, how you eat can make or break you.

Ultra-runners have been reported to burn around 16,000 calories in 33 hours, and Tour de France cyclists expend about 7,000 calories per day for 21 days. That’s way above what the body has on board, so you have to consume fuel while you’re racing to stay competitive.

It was initially thought that the body could only tolerate 60 grams of carbohydrates per hour (the primary fuel source during this type of activity). Any more would cause your stomach to rumble. However, some clever scientists later discovered that by using a combination of sugars (a mix of glucose and fructose), it was possible to increase the rate to 90 grams per hour, as each sugar follows a distinct path from the gut into the bloodstream.

A few small studies followed, one showing that as much as could be tolerated; however, the guidelines remained at 90 grams per hour, with 120 grams not being unreasonable.

Pushing Boundaries

In sports science, it has historically been the case that athletes try things then scientists figure out why it does or doesn’t work, rather than the other way around. In this case, there have been recent reports of athletes consuming over 200 grams of carbohydrates per hour during cycling.

Take Sam Long, for instance, who is training for the Ironman World Championships and recently documented what he ate during a huge training day (9:41 in the video below). During a 200km (~6-hour) bike ride, he consumed 800-900 grams of carbs. Cameron Wurf consumed over 200 grams per hour en route to a world record Ironman bike split in 2024. But are they actually burning those carbs and using them for fuel? The only way to know is to test it.

Embracing the Science

Scientists traditionally test this in the lab with a method called isotope tracing. It involves ever so slightly altering the chemical structure of the carbohydrates you consume (they add an extra carbon atom). Then, they measure the carbon dioxide you breathe out and can determine how much is made up of the chemically altered carbs versus the carbs stored within your body.

Obviously, most cyclists don’t have that luxury, unless you’re working with scientifically inclined coaches like Olav Aleksander Bu or the legendary Asker Jeukendrup, who now heads up Sport Strategy and Sport Nutrition for Red Bull-Bora-hansgrohe.

The reason it matters is because instead of blindly following guidelines, you can figure out how much of what you consume actually is making a difference. You could be consuming 90 grams per hour but only burning 65 grams, essentially wasting an entire energy gel every hour. You can also “train your gut” to tolerate more carbs, and this test would be a convenient way to see if that actually works for you.

Fortunately, sports scientists are bringing this technology to the field and using it with elite athletes during training. A new company, ExoAnalytics, founded by nutrition and sports scientists George Impey and Jamie Pugh, offers a product that allows consumers to conduct this test themselves. It has already been reportedly taken up by professional cycling teams. Although the data isn’t publicly available yet, they have claimed some elite cyclists can burn up to 180 grams of the carbs they consume on the bike.

There’s been a recent nutrition revolution in cycling, and the unique intersection between science and sport will only push performance to new heights.