23 July 2017

Froome Wins 4th and We're Nearly Perfect!

After his performance in the Alps and in yesterday's time trial, there was no doubt that Chris Froome would win his fourth Tour de France.  He now has a three-peat (should I send Pat Riley money for using that term???).  Froome didn't win a stage this year, but was clearly the best cyclist.  Staying near the winners in the mountains and in the time trials, Froome was simply better than everyone else.  His Team Sky mates played a large role in his victory.  It doesn't hurt to be supported by a powerful team!

Dutch cyclist Dylan Groenewegen won today's final stage.  How did our model perform today?  We saved our best for last, as you'll see below.
  • Stage 21:  2h 25' 39" (actual), 2h 25' 50" (prediction), 00' 11" slow (0.13% error) 
As tough as it is to predict the mostly-ceremonial final stage, I'm thrilled to end this year's Tour de France with a near-perfect prediction.  How did our model perform overall?  After summing the stage-winning times, I found we were 1.11% slow.  I'll definitely need to spend time thinking about how much athletes and technology have improved since last year.

I never cease to be amazed by elite athletes.  A total of 167 cyclists finished the Tour de France.  I would be hard-pressed to finish a long flat stage during daylight hours.  As for those grueling mountain stages, forget it.  I need more time in the gym!  My model estimates energy burn, i.e. internal energy burn with an average efficiency of about 20% and not just energy output needed to power the bike.  During the entire race about 115,000 Calories could have been burned.  Published cyclists' data may be below that number, but an estimate has to be made of internal energy efficiency.  Our published papers on Tour de France modeling cite sources that are consistent with our energy estimates.  The point is that a LOT of energy is burned during the three-week race.  At 550 Calories apiece, those 115,000 Calories amount to nearly 210 Big Macs.  That averages to 10 Big Macs per stage!  I don't recommend eating Big Macs before cycling, but it does give you some idea of how much energy those cyclists burn each day.  You may have heard that 3500 Calories matches the energy content in a pound of fat.  That's roughly true, but you may have to burn about twice the Calories to get a pound of fat off because of the complicated way the body converts energy.  Either way you think about it, 115,000 Calories represent one or two bowling balls of fat weight.  No wonder elite cyclists stay in such great shape.  Their job is a wonderful form of exercise!

I once again thank rising high-school senior Ryan Wainer from New York for his work this year.  He acquired all the terrain data, which led to a successful set of predictions.  How successful?  We had one bad prediction with Stage 5 (9.24% error) and five good-a-decade-ago-but-want-to-do-better-today predictions in the error range of 4% - 8%.  But that leaves 15 predictions to better than 4%, 11 of which were better than 2%.  Five of those 11 were better than 1%, including our best prediction today.  A nice way to end!


  1. As usual, I enjoyed reading your posts about the Tour de France. Looks like you had another good LC student working with you on this project. Great to see how well you did, and especially nice that you finished with the best prediction!

  2. Hey Eric,

    I thought you might be interested in the following paper. It discusses a plateauing effect of calorie expenditure from physical activity. This being their key chart: https://breddydotorg.files.wordpress.com/2016/02/steps-and-calories-burned-relationship.png

    The theory: https://breddydotorg.files.wordpress.com/2016/02/additive-vs-constrained-hypothesis-calories-burned.png

    The gist being an apparent compensatory effect over a certain threshold. Where if you're burning a ton of calories from physical activity, the body will lessen calorie expenditure elsewhere to try and balance out. Think female endurance athlete who has amenorrhea as a form of lessening calorie demand. (This has been found regardless of calorie intake.)

    It's a very interesting finding and theory, because it provides rationale for why exercise provides other health benefits, like less inflammation. Where perhaps the body will only expend so many calories. If enough are on exercise, then it won't expend calories on e.g. inflammation.

    Link to the paper: http://www.cell.com/current-biology/fulltext/S0960-9822(15)01577-8

    (Wrote about it myself too: https://b-reddy.org/2016/03/21/new-insights-as-to-why-you-cant-avoid-exercising/ )

    Enjoyed your conversation on StarTalk.