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Monday, July 23, 2007

How to feed a cyclist

Roll on more tour posts! Following the pre-Stage 15 prediction, we will keep the posts coming as thick and fast as the attacks we have seen in Le Tour the past couple of days.

In this short post we will get into what it takes to fuel a cyclist through a stage race like Le Tour, and this will serve as a spring board to talk more in the future about exercise metabolism and all its implications. So we all know that the energy demands placed on tour riders are pretty astronomical, but let's think about the basic energy needs of a 75 kg cyclist. His resting metabolic rate, or the amount of energy he requires to sit there the whole day and not do anything, probably clocks in at around 1500-1800 calories, depending on his body mass. That is the amount of energy he requires just to keep his body alive and functioning.

Before we delve into energy requirements, it is first important to remember that the cost of moving your body through space is a function of the distance, and not the speed at which you do it. So if you run a mile in 3.5 min or 10 min, it will cost you the same amount of calories. Recall that power is the rate at which work is performed (Work / Time), and so of course, if you run the mile in 3.5 min then you have an incredibly high power output---that is, you burn the same number of calories but in a much shorter time, so that rate at which you burn calories is high.

So how many calories does it cost to cycle a 180 km flat stage? Since cycling is a pretty efficient activity, it costs a 75 kg athlete in the range of 0.3-0.4 calories per km per kg. To be more meaningful, it costs him about 25-30 calories per km. The bottom line here is that a 180 km stage will cost our athlete in the range of 4000-5500 calories, depending on how much pedaling he is actually doing and how much sitting in the bunch he is doing. Our cyclist's total energy expenditure for one day is his resting plus his exercising energy expenditures. Therefore 1500 + 4000 = 5500 calories (we have taken the low end of the range here). "Woo-hoo!" I can hear you saying, "He can eat whatever he wants!" Well, yes, but given the fact that he is on the bike for four or more hours during the day, and feeling pretty tired for another few hours after the stage, plus the "anorexic effect" of exerciswe, plus 8-10 hours of sleep. . .suddenly he has to consume large amounts or calories in not so much time. In fact, if we assume he is "occupied" for up to 16 hours a day with riding, sleeping, and just generally feeling fatigued, he has only about 7-8 h to ingest 5500 calories, which works out to about 700+ calories an hour (for each hour he is free to eat).

However, Klaas Westerterp and his colleagues in Maastricht actually measured the energy intake and estimated the energy expenditure in five cyclists in the 1988 Tour de France. Their average intake was almost 6000 calories per day, while their average expenditure was nearly 6100 calories per day---indicating that these cyclists did a remarkable job of (nearly) maintaining energy balance. They accomplished this by ingesting 49% of their energy while riding, which amounted to whopping 94 g of CHO per hour during each stage! This makes it substantially easier to meet energy requirements during the 7-8 h when they are not racing or otherwise occupied.

So those are the basic demands and needs for these tour riders, yet this is only an appetizer, if you will excuse the play on words here, becasue what these guys eat and when they eat it both have important implications for their performance and recovery from day to day.

Come back for more posts on the optimal diet for a tour cyclist, and in the mean time enjoy the racing!

R & J

2 Comments:

BenP said...

do you know where I could find the same thing for running and for every weight ?

Ross Tucker and Jonathan Dugas said...

Hi Ben,

Thanks so much for your question and for your interest in our blog.

There are several sources for more information on this.

First, you can get the American College of Sports Medicine's Metabolic Calculations Handbook:

http://www.amazon.com/Metabolic-Calculations-Handbook-American-Medicine/dp/0781742382/ref=sr_1_1/104-4343573-5929549?ie=UTF8&s=books&qid=1185291629&sr=1-1

You can also try these sites for a more rudimentary answer:

http://www.chartsgraphsdiagrams.com/HealthCharts/calorie-requirement.html

and

http://www.stevenscreek.com/goodies/

The bottom line is that the energy required to move your body is a function of the type of activity, the body mass, and the distance.

If you buy ACSM's book, you can even calculate how much energy it will cost you to run a certain distance at a certain speed---that is, you can calculate how much oxygen you will use per minute.

Good luck and let us know if you have any other questions on this!

Kind Regards,
The Sports Scientists
Ross and Jonathan