Imagine that you start pedaling beginning of stage 12 of this year’s Tour de France. Your very first task would be to hike approximately 20.6 miles (33.2 km) to the top of Col du Galibier in the French Alps while gaining approximately 4,281 feet (1,305 m) in elevation. But this is only the first of three big climbs of your day. Then you face the top of Iron Cross Pass then finish the 165.1 km (102.6 mile) stage by taking on the famous Alpe d’Huez climb with its 21 sinuous turns.
On the fittest day of my life, I may not even be able to complete stage 12 – let alone do it in close to the roughly five hours the winner will take to complete the ride. And leg 12 is just one of 21 legs that must be completed within the 24 days of the tour.
I am a sports physicistand I have modeled the Tour de France for almost two decades using field data – like what I described for step 12 – and the laws of physics. But I still can’t imagine the physical abilities needed to complete the most famous bike race in the world. Only a few elite humans are able to complete a Tour de France stage in a time measured in hours instead of days. The reason they are able to do what we can only dream of is that these athletes can produce massive amounts of power. Horsepower is the rate at which cyclists burn energy, and the energy they burn comes from the food they eat. And on the Tour de France route, the winning cyclist will burn the equivalent of around 210 Big Macs.
Cycling is a game of watts
To make a bike move, a Tour de France rider transfers energy from his muscles, through the bike and to the wheels that push back to the ground. The faster a cyclist can produce energy, the greater the power. This rate of energy transfer is often measured in watts. Tour de France cyclists are able to generate enormous amounts of energy for incredibly long periods of time compared to most people.
For about 20 minutes, a fit recreational cyclist can constantly 250 watt to 300 watt. Tour de France cyclists can produce more than 400 watts for the same period. These pros are even capable of reach 1000 watts for short periods of time on a steep climb – about enough power run a microwave.
But not all the energy a Tour de France cyclist puts into their bike is transformed into forward motion. Cyclists struggle with air resistance and friction losses between their wheels and the road. They get help from gravity on the descents, but they have to fight against gravity on the way up.
I incorporate all the physics associated with rider power output as well as the effects of gravity, air resistance and friction in my model. Using all of this, I estimate that a typical Tour de France winner should average out around 325 watts over the roughly 80 hours of racing. Remember, most recreational cyclists would be happy if they could put out 300 watts for just 20 minutes!
Turn food into miles
So where do these cyclists get all that energy from? The food, of course!
But your muscles, like any machine, cannot convert 100% of food energy directly into energy production – muscles can be anywhere between 2% efficiency when used for activities like swimming and 40% efficiency for the heart. In my model, I use an average efficiency of 20%. Knowing this efficiency as well as the energy production needed to win the Tour de France, I can then estimate how much food the winning cyclist needs.
The best Tour de France cyclists who complete all 21 stages burn around 120,000 calories during the race, an average of nearly 6,000 calories per stage. On some of the toughest mountain stages – like this year’s Stage 12 – runners will burn close to 8,000 calories. To compensate for these huge energy losses, cyclists eat delicious treats such as jam rolls, energy bars and appetizing “jellies” so you don’t waste energy chewing.
Tadej Pogačar won the 2021 and 2020 Tour de France and weighs only 146 pounds (66 kilograms). Tour de France cyclists don’t have a lot of fat to burn for energy. They must continue to put food energy into their bodies so that they can produce energy at what seems like a superhuman rate. So this year, watching a Tour de France stage, notice how often the cyclists eat, now you know the reason for all that nibbling.
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This is an updated version of a story originally published on June 24, 2021.
