TV coverage of sports is prone to exaggeration. As much as I love the spectacle of the Tour de France, not even Phil and Paul are immune to exaggeration. But, one thing that is not embellished is the quantity of food that it takes to sustain energy throughout the Tour. Have you ever thought about how much food the cyclists must eat to get through a 3-week tour? In other words, how much food does it take to sustain 4000 km of racing including mountain passes, time trialling, and incomprehensible average speeds?
Researchers in Holland performed the first measurements of energy consumption during the Tour de France. The cyclists in their research group consumed 24.7 megajoules/day (5,900 cal/day) with a highest average value for a single day being 32.4 megajoules (7,750 kcal). That sounds like a lot and it is, but to give you something a little more tangible about how much food that really is, I will steal an example from Rabobank's team physiologist Asker Jeukendrup. Professor Jeukendrup likes to relate the quantity of food to cheeseburgers, a quantity most non-vegetarians understand. Professor Jeukendrup relates that on average a cyclist has to consume 19 cheeseburgers a day during the Tour. This is definitely a large amount of food and is complicated more so by the fact that the cyclists are on their bikes racing for a good portion of the day when it is harder to eat. So if it is broken down further, a typical pattern is the following. When the cyclists wake up they consume 4 cheeseburgers for breakfast. On the bike throughout the stage they eat another 5 cheeseburgers. After they race they immediately have to choke down 2 more cheeseburgers. Then comes dinner where they eat an incredible 6 cheeseburgers. But this is not even the end yet, before going to bed another 2 more cheeseburgers are consumed. Such is the life of a tour cyclist as related by cheeseburgers. Could you imagine eating that much, do you think it is even possible to eat more? I will actually build a case here that these athletes are eating as much as physiologically possible and by not being able to eat any more, they are limiting how fast they can go.
The same Dutch researchers mentioned above also measured daily average energy expenditure during the same Tour that they measured energy intake. They found that on average the cyclists expended 29.4 – 36.0 megajoules/day (7020 – 8600 cal/day). In other words energy expenditure roughly matched energy intake. This amount of energy expenditure is 3.6 – 5.3 times the amount of energy needed to support our body at rest (resting metabolic rate). In the early 1980's a physiologist named Kirkwood took all the data available at the time on mammals and birds to determine that across species the maximum energy expenditure possible is about 4-5 times resting metabolic rate. In other words, something unknown keeps all species from being able to use more energy than 4-5 times resting metabolic rate. Notice that cyclists during the Tour de France were operating right at the proposed maximum energy expenditure. Therefore, the energetic demands of a 3-week grand tour may be the data point representative of homo sapiens on Kirkwood's graph.
Because energy storage is not unlimited in our bodies, how much energy we can expend must be met by energy intake. As demonstrated above, the athletes were expending roughly the same as they were taking in during the Tour. Therefore the question now arises, is the amount of food the athletes take in limiting how much they can expend. In other words, it may be that it is extremely difficult to eat more than 30 megajoules/day and this therefore, limits our energy expenditure to 30 megajoules/day. We often hear of cyclists having a stomach ailment during a tour and that having an iron stomach is a benefit for those in a grand tour. It may be that these athletes are impinging on their maximum ability to consume food. Since they cannot consume even more food, their maximum ability to expend energy may be compromised.
I would like to make one more interesting point related to this energy in and energy out talk. Recently there was an effort by the Vuelta a España organizers to shorten stages to make them more human and to discourage doping. However, what they found was that the riders simply rode faster over the shorter courses. Therefore even though the stage race was shorter, by racing faster they were expending the same amount of energy as a longer stage. It may be that the riders are so capable of pushing themselves that no matter how long or how short the race, they are on the physiological limits of energy expenditure. Further, since the ability to produce energy day after day is dependent on being able to get that energy back in to the system, it may be that physiological performance at a tour is limited by how much food can be consumed. So, is shortening stages going to make things any easier? Not likely.
To summarize, how much do riders eat? A hell of a lot. So much in fact that for digestive reasons, or otherwise, it may be the physiological limit of what is possible to eat. Further, this inability to consume more food could ultimately determine how fast the riders are capable of going over 3 weeks.
Please note that I say "maybe" a lot in this particular column. That is because I want to emphasize that this is just a hypothesis conjured up by me and is not proven in any way. It would be quite easy to support this hypothesis with currently available data, but in no ways would it be definitive. So, for now treat it as "food" for thought.
I take no credit for the cheeseburger example as the credit belongs fully to Professor Jeukendrup.
Ben Miller is Senior Lecturer in Exercise Physiology. He did a PhD at the University of California – Berkeley and a Post-Doc at the Institute for Sports Medicine, Copenhagen before arriving in Auckland. As a departure from his life in a closed scientific box safe from the realities of the world, he is a cyclist regularly taking his life in his own hands on the streets of Auckland and in the local club racing and criteriums. Ben's wife is much more successful at cycling having competed full-time in Europe and the US for the last 4 years.
For more reading on scaling and TDF energy expenditure see;
1) Kirkwood, JK. A limit to metabolisable energy intake in mammals and birds. Comp Biochem Physiol. Vol 75A: 1-3. 1983.
2) Saris WHM, et al., Study on food intake and energy expenditure during extreme sustained exercise: The Tour de France. Int J Sports Med 10: S26-S31, 1989.
3) Westerterp KR, et al., Use of doubly labelled water technique in humans during heavy sustained exercise, J Appl Physiol, 61(6): 2162-2167, 1986.