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Data transparency in cycling: necessary, utopian, and a complete can of worms

July 19, 2015

This year’s Tour de France is developing into a bit of a split race, being both exciting by stage and predictable by General Classification (GC).  This was most clearly demonstrated by the blistering performance of yesterday’s stage winner Steve Cummings of MTN-Qhubeka (the African team’s first stage win, on Mandela Day, no less), followed by Chris Froome hoovering up all attacks against him.  It was an eventful ride for Team Sky, with fists, saliva and urine apparently being thrown at them.  They are currently the sport’s bad guys, for no reason other than dominance.  The last team to dominate like Sky did was one of the liveries led by Lance Armstrong, and Sky’s tactics and public relations stance continue to draw uncomfortable parallels with the Armstrong era.  This suspicion has led to calls for Sky (and others) to be more transparent about their power data in particular, since the view goes that teams with nothing to hide should hide nothing.

Something something Armstrong, something something Froome. Right, let’s SCIENCE… [Forget personalities, there’s a link in two paragraphs time in which the awesome David Wilkie uses very simple power modelling to make a bicycle fly.]

Power output and the physiological response to exercise

Mountain stages in the Tour are critical to success.  One bad day in the mountains can cost you the race, and a good day can get you a Yellow Jersey.  In contrast, sprint stages rarely produce gaps in the GC, and time trial stages are predictable and (to within a minute or so) run to form.  That’s problematic if you’re on the wrong side of the minute, but not fatal.  Gaps of over 5 minutes are sometimes seen in the mountains.  In a mountain climb, where air resistance plays a more limited role, the rider who can sustain the highest power, and thus (bike and body mass accounted for) the highest speed for the duration of the all the climbs, is likely to win the Tour.  Time trial specialists cannot win the Tour with time trials alone.  They must train to climb (contrast Boardman’s Tour performances with those of Wiggins – riders with very similar initial backgrounds but very different training approaches to the road).

Because sustaining a high power output on a climb is crucial, there has been a great deal written about the limits of what is possible.  I am not going to add to this debate, as in my view without direct measurement of power as well as an understanding of the rider’s physiological capacities (aerobic and anaerobic) there are too many assumptions to be sure that a conclusion about whether something is possible or not can be drawn.  There are performances that might look suspicious, but a 4 min mile performance in running would have looked suspicious in 1935.  By 1995 it was considered slow.  We do, however, know a few things about what determines sustained power, thanks to scientists like AV Hill, David Wilkie, and a number of others.

The physiological response to exercise depends on the power output you produce.  For “moderate” exercise, muscle oxygen uptake rises rapidly and reaches a steady state.  Blood lactate either does not rise or rises only transiently.  At these work rates, exercise can be sustained for many hours.  For “heavy exercise”, when you exceed the lactate threshold, oxygen uptake takes longer to stabilise and does so at a higher value than you would predict from steady state responses to moderate exercise (in other words, you are less efficient).  This is the result of a “slow component” of the oxygen uptake response that develops after about 2 minutes of exercise and stabilises after 15-20 minutes.  In the heavy domain, exercise can be sustained for between 45-60 min and about 3-4 hours.  For “severe” or “high-intensity” exercise, the oxygen uptake slow component does not stabilise (and nor does any other metabolic response) until maximal oxygen uptake (VO2max) is attained.  Exhaustion inevitably follows soon after this occurs. The “severe-intensity domain” commences when you exceed the critical power (CP).  The CP, in turn, represents the asymptote of the power-duration relationship, first noted by AV Hill in 1925.  We’ve written a few papers about these concepts, which you can find here (free) and here (not free).  The power-duration relationship can be defined by as few as two parameters, namely the CP and a parameter to define the shape of the curve, denoted W’.  The CP is thought to reflect the power of the aerobic systems of energy delivery and the W’ is thought to reflect the “anaerobic capacity”, although we know this is a little simplistic. It is the power-duration relationship that is important for working out what is and is not possible when cycling up a hill.

Defining possible and impossible

If you know the values of CP and W’, and you know the power demand of a task, you can make a clear prediction about what the time limit of the task is. The equation, for those who want it, is:

Time limit = W’/(power output – CP)

The problem is that the above parameter values will vary between athletes and will vary day to day.  The parameters and the underlying physiology that determines them can also be influenced by various acute interventions (like glycogen depletion, for example), which adds further uncertainty to any “back of the envelope” calculations that you might wish to make. To know if any performance is abnormal, you need to know what the power-duration parameter values actually are. Consider that in an elite cyclist with GC ambitions might have a CP of about 380-440 W, and a W’ of 20-30 kJ, both of which will depend, to some extent, on body mass.  This means that to complete an effort lasting 40 minutes, with a W’ of 25 kJ and a CP of 420 W, the “normal” power output sustainable for this duration would be 430 W, or 6.1 W/kg for a 70 kg rider.  Notice here that the contribution of the curvature constant to long duration efforts is quite small (about an extra 10 W over 40 min) and thus the most crucial determinant of mountain performance is the maximal sustainable power output, CP.

One reason why I don’t think fixating on a particular W/kg value as “possible” or “suspicious” really works is that it all depends on the value of CP.  This value is unknown and variable!  Obviously, for a 70 kg rider to sustain 6.1 W/kg without drawing on the W¢, CP would need to be at least 430 W.  I don’t think that is unreasonable, given previously documented hour record performances and the power outputs produced during them (Bassett et al., 1999).  To sustain 430 W would require an oxygen uptake of approximately 5.3 L/min (O2 cost of ~10 mL/min/W, plus ~1 L/min for the O2 cost of spinning the legs at 90-100 rpm), which, if capable of utilising ~90% of VO2max, would predict a VO2max of 5.8 L/min or 84 mL/kg/min.  This is high, but certainly not unheard of.  Sustaining 85% of these figures would require a VO2max of 89 mL/kg/min.  That is still not impossible.  And this is all assuming a normal mechanical efficiency.  Efficiency would decrease due to the development of a slow component of oxygen uptake, but this would add no more than about 200 mL/min to the tally (that is, oxygen uptake would remain submaximal even with this factored in).

Knowing the possible

The above calculations are hypotheticals based on reasonable estimates.  The numbers accompanying Froome’s (or Nibali’s or Contador’s or…) that appear on the internet are just as hypothetical.  In short, we have no direct numbers for either physiological capacity or performance for GC riders at the time of the Tour.  Values estimated from those recorded in other parts of the season are likely to underestimate the capacity of a rider who has peaked and ridden conservatively in much of the first week of racing.  In addition, direct measures of rolling resistance, wind speed, temperature, altitude, and so on, are also absent.  To know what’s possible would require direct power-duration measurements from Froome immediately before the Tour, as well as calibrated power data during each and every stage.  It is likely that Sky possess both data sets.  They most likely have a variety of physiological measures that could corroborate the power-duration data (i.e., the VO2max, efficiency and LT data would likely fit in the same general picture).  But they refuse to place these data in the public domain.  Should they?  The scientist in me says yes.  The sports fan in me says maybe.  The pragmatist in me says that there is next to no chance of these contemporary data ever seeing the light of day.

For one thing, Froome’s consent would be needed to release these data, and even if that consent was given, where would the data be stored and how would access be gained?  If Froome releases his, every rider in the Peloton should be obliged to release theirs, lest there be any accusations of unfair treatment.  The teams are highly unlikely to want to do this for competitive reasons.  It’s much the same reason why Formula 1 teams do not release telemetry data in real time – a good rival engineer would identify engine modes, brake balance, tire wear etc and use that information to the team’s advantage.  The sport would become even more about who has the best support crew rather than the best performer.

A less problematic point is that not all teams use the same power-measuring devices.  Moreover, where on the bike the power is measured also matters.  Although often measured at the crank or the rear wheel hub, it’s the power transferred to the road that counts (producing forward propulsion), but the power actually produced on the pedals that costs (in terms of physiological demand).  Frictional losses and rolling resistance (though presumably minimised) will also differ, adding errors to any calculations of who produced watt, where and when…

The Future

There has been some chatter on Twitter and elsewhere of power files from races being used as part of the Athlete’s Biological Passport in cycling.  I can see some merit in this, as within each athlete, performances can be compared to their power-duration relationship, their physiology and their blood parameters already used.  The observation of abnormal power outputs alongside sudden changes in, for example, the Off-score, might trigger closer scrutiny of that athlete in the coming months.

Finally, I can see the potential for power data from grand tours being released following an agreed embargo period.  This would serve an educational and scientific purpose of providing a rich seam of data to be used by anybody who wanted it.  Those data could also be used as part of a retrospective anti-doping case.  But they’d only ever be part of the story.  If there was reasonable circumstantial evidence of doping in the absence of a positive test (like the Armstrong case, for the most part), then power files could weight to that case.  But it would only be small given the number of variables involved in ultimately producing power output.

I’ve almost certainly not done this issue justice, but the above thoughts lead me to conclude that the question of data transparency in cycling and what its potential uses are does not have any easy answers.


The contentious and irrelevant bit:

Armstrong’s shadow

The similarity between Armstrong-era cycling and today ends with what is written above.  Quite a few people have asked David Walsh, the man who was instrumental in taking down Armstrong, why he is not asking Sky and Froome tough questions.  I personally think that is wrong-headed.  Armstrong’s transformation post-cancer was mind-blowing, whereas Froome’s ascent has been more incremental.  Add to that the accumulation of damning evidence throughout Armstrong’s career, covered up by Armstrong with the help of the UCI, and in that case Walsh could ask questions about tangible things in Armstrong’s closet.  Froome’s closet is bare by comparison, save for a TUE and some stunning performances on the road.  So there was good reason to pursue Armstrong, but much less to pin on Froome and Sky.  This is why calls for data transparency are timely.

[EDIT: I’ve got quite a few comments about the LA/CF comparison I made above both here and elsewhere.  I’ve a good mind to delete it because I think it detracts from the point I’m trying to make (that power output is interpretable in context but it’s always likely to be very difficult).  I’m not going to delete it, however, because it would make the post more boring, and writing really bloody boring stuff is something I’m already pretty good at.  My point to those arguing over this is that (like the rest of the post, actually) context is everything.  We know most of the details surrounding Armstrong’s “inverted U-shaped” career progression, in which he went from an aggressive stage racer/breakaway specialist to cancer patient to GC domination.  In this, he went from not really being notable as a climber to dropping Pantani. That’s astonishing.  Froome burst onto the scene in late 2011, but had been with Sky for about 18 months before that, and showed some potential between bouts of illness and injury.  The impact of these is not certain because, again, of the context. Sky, due to its links with British Cycling, was and still is awash with riders who are good against the clock, so he wasn’t in the team to be the time triallist.  He was clearly there to be part of the Sky train, in a team hell-bent on GC success with Bradley Wiggins.  In that context, Froome’s rise to prominence was not particularly fast, but was perhaps unexpected given the circumstances at the time. Importantly, he didn’t completely change his style of riding to break through.  I am not naïve enough to appreciate that there aren’t other explanations, but, again that’s not what the post is about, and I’ve tried to avoid drawing any of those conclusions. Back to the day job…]

23 Comments leave one →
  1. July 19, 2015 9:15 pm

    Reblogged this on .

  2. Patrick Behan permalink
    July 19, 2015 9:38 pm

    Nice article

  3. Andy Giddings permalink
    July 19, 2015 10:38 pm

    Interesting and thought provoking article. One of the first I’ve seen to highlight the difficulties related to data collection and comparison, notwithstanding the issue of linking power to predictable results, thanks

  4. Kenneth Parker permalink
    July 19, 2015 11:06 pm

    “Armstrong’s transformation post-cancer was mind-blowing, whereas Froome’s ascent has been more incremental. ”

    Care to elaborate? Because to me, that sounds like an outright lie. Froome’s transformation is far more mysterious. He went from a pure domestique to an elite climber in the Vuelta 2011. At least the pre-1999 Armstrong was a world champion before he became the suspicious demigod of cycling.

    • July 19, 2015 11:24 pm

      Yes, hard to tell a domestique’s strengths because they are a domestique who may be told how to race, being a junior team member. The incremental aspect of Froome’s career is that it took 2+ years to become a GC contender. With his frame he was always going to be a climber.

      But my post was not about Froome or Armstrong (I used them as a “way in” to the issues). Instead, it was about how power and physiology are intertwined and what this means for the interpretation of performance. I’m far less interested in the personalities and the innuendo flying around, whether justified or not, so I don’t really appreciate the accusation of lying here.

      Thanks for commenting all the same.

      • Kenneth Parker permalink
        July 20, 2015 12:28 am

        Fair enough. You just made like sound like Armstrong was a nobody before winning the Tour. That’s not the case. He was never an elite climber or time trialist, you’re right about that. But a talented punchy classics specialist in his pre-doping days. Similar to Gerrans, Kwiatkowski and Gilbert. A great talent who had the potential to win Amstel, Liege or perhaps Lombardia, but never a Grand Tour.

        And thank you for the reply! While I don’t agree with all of it, I found your analysis to be very enlightening and constructive.

      • July 20, 2015 12:36 am

        Thanks for the clarification, glad you enjoyed the rest of the post.

      • flicksta permalink
        July 20, 2015 10:04 am

        Let’s not pretend that Armstrong wasn’t a doper before his cancer – after all, he ackknowledged in the treatment room that he’d taken EPO, HGH, testosterone and steroids. He was doping before he was 25

  5. Simon Evans permalink
    July 19, 2015 11:59 pm

    “With his frame he was always going to be a climber.”

    Before winning the TdF, he medalled in the Olympics as a time triallist. Earlier in this year’s Tour, he dismissed Tony Martin’s chances of holding onto the yellow jersey once the race hit the mountains, since he was a time trialler. Should we be concerned about this? Why don’t these same rules apply to him? After all, when the route was announced, his reaction was to suggest he’d miss the TdF as he felt there was too little time trialling.

    • July 20, 2015 12:35 am

      Transition from time triallist to climber possible if you shed mass but maintain power (Wiggins took this approach, Boardman didn’t…). My guess (and it is only a guess) is that Froome did the same. In the Olympics, climbers won’t win medals, so you have to be a stage racer or a time triallist and train as such if you want success.

      • Simon Evans permalink
        July 20, 2015 12:41 am

        Okay. That must generally be a challenge then, otherwise we’d see more TT champs transitioning to Tour winners.

        Wiggins managing both within the space of a few weeks is perhaps an anomaly by that theory.

      • July 20, 2015 3:17 am

        Doesn’t the statement “Transition from time triallist to climber possible if you shed mass but maintain power” fit firmly in the category of “easier said than done”? There isn’t really any dispute that major weight loss is the distinguishing feature of some of these transformations. What puzzles me is how these emaciated figures deliver the kind of power necessary to post times comparable to the known doper era? I am not saying they can’t, I just would have thought one would reach a point of diminishing if not negative returns where losing any more weight would result in loss of power and slower times. That point (to the naked eye) does not yet appear to obey limits in terms of what level of weight loss is helpful to improve power/weight ratio when gravity going up mountains is the biggest variable before it introduces a lack of strength to propel the skeletal body+bike forwards.

        I too raised an eyebrow about Armstrong’s rise being mind-blowing whole Froome’s was incremental. I’m not sure how many riders in Grand Tour history have gone from not being selected and not about to have his contract renewed, then making the team to replace a sick member who couldn’t start, and then finishing second! ‘Incremental’ is not a word I would use to describe Froome’s improvement from August 2011 to September 2011!

        This is an excellent article, and I like the idea of a full download of data being available after an agreed embargo period for academic research. I would also like to see a fact sheet at least of all GC tour stages documenting the many relevant ambient and environmental conditions from wind to tarmac quality that you mentioned above.

        Thank you for your reasoned and positive contribution.

      • Peter Upface permalink
        July 20, 2015 9:57 am

        Simon, almost 90% of recent Tour winners have been incredible at the Time Trial. Armstrong obviously but Contador, Wiggins, Nibali (4th in the ITT) and Cadel Evans took the Yellow from Schleck in the ITT.

        For reasons discussed in the article you can see why this would be the case. There are, on occasion, some very good road TTs who don’t fit this mould (Fab Cancellara, Tony Martin), they are heavier and can therefore sustain a higher power output on flatter TT stages which translates to a few seconds advantage. However there aren’t many of these because they aren’t needed on the road, Tony Martin is essentially employed to tap out an incredibly high tempo in the leadout train to stop anyone breaking off the front coming up to the sprint. Cancellara is a puncheur who hopes to get in a breakaway, grab a few metres on the run in and time trial to the finish.

        What this article only briefly mentions is the technological part of Sky’s success. What the rider does vs what the bike outputs is not the same and Sky have huge resources and incredibly clever people eking out everything.

      • Simon Evans permalink
        July 20, 2015 12:31 pm

        Hi Peter, yes, you’re right, they’re generally very competitive at both TT and climbing. Given that weight is much less of an issue for TT I would naively have thought that it was more closely related to absolute power output (aerodynamic drag being the main force slowing you down on a flat road). In a sport with a long tradition of sub-disciplines in which individual riders excel (puncheurs, climbers, time triallers, sprinters, etc) it seems a little puzzling that we witness individuals able to rise to the very top in multiple sub-disciplines. But maybe that’s my naivety, and it’s always been thus.

        The technology argument I feel sceptical about – the bicycle is already a very efficient machine: as I understand it, almost all of the rider’s effort is translated into forward motion and very little is wasted. So even with millions of dollars of investment, there’s a fairly small improvement that is possible. Back in the USPS days, we were also told that technological investment (reduced Q-factor, wind tunnels) underlay much of Lance’s Tour dominance. And while Trek benefitted astronomically, we now know it was just a cover story.

  6. July 20, 2015 12:29 am

    Sky have used Stages power meters since 2014. That data will likely be as un-useful as the randomly variable power estimates made from climbing speeds.

    • Simon Evans permalink
      July 20, 2015 12:38 am

      Why would they fit them if they weren’t useful?

      All estimates contain random variation.

  7. July 20, 2015 1:10 am

    Reblogged this on TeflonDub in the New World and commented:
    Excellent piece on the pragmatics of managing cycling power data.

  8. macstaffs permalink
    July 20, 2015 5:47 pm

    What most people miss about Froome`s ‘sudden’ ascent to GC greatness is the bilharzia he suffered with throughout his early career. Once he got rid of this debilitating disease he started to get the results in 2011 his early mentor Robbie Nilsen always believed were possible.

    • Paula permalink
      July 25, 2015 3:08 am

      Spot on. The bilharzia is something Tucker in particular completely ignores in dismissing Froome’s early career.

      People also forget that Froome grew up at high altitude – he lived in Nairobi (1,680m) until he moved to Jo’burg (1,750m) after primary school. He began cycling in the Rift Valley. It’s highly likely that living at altitude and being a physically active kid he has long term adaptations to altitude (epigenetic) that benefit him today. Wouldn’t surprise me if like Cadel Evans there wasn’t a whole lot of TV growing up so he had to make his own entertainment the old fashioned way by playing outside. Here’s what his early development was like

      Greg Lemond is another Tour winner who grew up at altitude – he lived in Tahoe (1,897m) until he was 12 before the family moved to a farm outside Reno (1,300m).

  9. Andy Giddings permalink
    July 21, 2015 10:30 pm

    Dr Burnley, would be interested to hear your views on the release of limited power data by Team Sky and Chris Froome today, if you have a chance?

    • July 21, 2015 11:05 pm

      Limited is the word! To me it all looked rather unexceptional for a GC contender, and seemed to make sense from the limited comparison with his 30 min and 60 min powers. Whether you consider the corrected or uncorrected powers reported, both are in the realms of possibility. Some have suggested inconsistencies with other riders measurement or estimates, which is always likely given differing power measuring devices and chainrings etc. I am a little puzzled by those questioning the accuracy of Sky’s data though, given that coaches and scientists working for British Cycling based almost the entire track programme on power measurement. They’ve been using it since at least 1996 and so they, and later Sky, have been in the field-based power measuring business as long as anybody. I think you can trust the data, but for a more complete picture the text file of power would need to be released. If I was in charge of Sky, I’d release all of Froome’s power files at the end of the season (there is no chance of them doing it now). If they did that, the rumours might die down. But there are, I think, a considerable number of people who could never be convinced by it. That’s a consequence of the sport’s recent history unfortunately.

  10. Andy Giddings permalink
    July 22, 2015 9:15 am

    Thanks for the response. I think that Sky were forced to react to the French TV “study” and were trying to at least do their best to contain the speculation arising. Not sure this has worked though, seems to be more a case of damned if you do and damned if you don’t. I hope that one outcome of this is a decent method of collecting and sharing power data across all teams (the power passport concept for example). However, the speed with which the cycling governing body moves is not encouraging me to believe this will be done before the next tour


  1. Semi-transparency, smoke, mirrors and an illustrative case | The Science of Sport

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