Monday, July 26, 2010
Tour power output reflections
Looking back on leTour - the post collection
Thank you for visiting The Science of Sport. Over the past few weeks, we've followed and attempted to analyse the performances of the very best cyclists in the world, and at worst, it's created some great discussion and back-and-forth. At best, it's shown that cycling may just be heading in the right direction in its fight against doping.
Earlier today, Greg Lemond mentioned our analysis in his blog at Cycling News under the title "data of optimism?" and I certainly share that sentiment. So for those arriving "late", below are the links to the three analysis we've done on the power outputs, courtesy data provided by SRM and Training Peaks.
Post 1: Power outputs from the Alps and Pyrenees
Post 2: The Col du Tourmalet - the showdown at 6W/kg
Post 3: Resolving discrepancies in the Tourmalet numbers
I'd encourage you to also read the comments, where you have really improved the overall quality of the debate with your own calculations and questions.
One of the big talking points in all these analyses is the issue of whether a performance is proof of doping. Of course, the answer is no. There are too many assumptions in the calculation of physiological implications of a given performance for it to be "proof". Also, things like tactics and weather and preceding stages affect a rider's ability to produce a given power output. However, when looked at in context and when those assumptions are "controlled" in order to create a 'best-case scenario', the picture is still, I believe, telling, and that is what the above posts are about. There comes a point at which the principle adds value.
Of particular interest given the debate before the Tour, is that not a single longer climb hit the power outputs that we've become accustomed to seeing in 90s and 2000s. Nor have they hit what we debated pre-Tour as the "suspect" power values of greater than 6.2, 6.3, 6.4 W/kg.
And while the 6.2 W/kg number got a lot of people riled, I really think it's telling that the very best climbers, with the highest level of motivation (on the Tourmalet) failed to hit those power outputs. Re that number - in a debate about "unrealistic performances", you have to commit to a value, even if only to illustrate a point. It does not mean this number separates the world into light and dark.
Even Contador and Schleck on the Tourmalet, in what was an absolute 'limit' performance, just touched 6W/kg as an average, and appear to have dropped right down towards the end of the climb (see post 3 above). To me, this largely validates the physiological principle that says that for every performance, there is a physiological 'cost' and at some point, the 'cost' becomes an indication of doping. In the words of Lemond, the performance becomes "believable".
There is no dividing line in the sand, no specific point at which you can say "got you". A rider at 6 W/kg may be doping, and one at 6.2W/kg (depending on the situation) may not, but there is a theory underpinning it and the change in this year's Tour is a positive sign, leading to the hypothesis made in those posts and by Lemond.
It's been a super Tour, with great individual performances on stages, and the confirmation of a rivalry between Contador and Schleck that will hopefully put cycling in the news for the right reasons. And hopefully, it's also produced a step in the right direction for the sport. Bring on 2011, hopefully a mountain time-trial, and another super-tight race!
Ross
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Posted by Ross Tucker and Jonathan Dugas on 7/26/2010 05:17:00 PM 31 Comments
Labels: Cycling
Saturday, July 24, 2010
Power output on the Tourmalet - resolving discrepancies
Ferrari: "6.42 W/kg". Everyone else: "Less than 6 W/kg". Who is right?
Thanks everyone for the great discussion in response to the post yesterday looking at the climbing power output on the Col du Tourmalet. As if often the case, your responses make the comments section to the post is better than the post, so if you have to time, you might consider reading it here!
However, a short post today, because something came across our twitter account yesterday and today mentioning that Dr Michele Ferrari has estimated the power output on the climb and his values contract those presented here yesterday. I was going to post this in the comments section only, but I felt it worth putting out, since the disagreement is so large, and from such an 'infamous' source, that it demands attention.
From the site 53 x 12.com, Ferrari writes the following:
"Col du Tourmalet, in the last 9 km they climbed at 1780m/h, equal to 6.42 w/kg."
You'll recall that we said yesterday that:
"My overall estimation is that they took 49:08 to climb what I believe to be the final 17.6km at a gradient of 7.6%. This gives a VAM of 1,633 m/hour, and a relative power output of 5.9 W/kg."
Even over the final 9.3km, after Andy Schleck attacked, we estimate a power output that is even lower than this. We wrote:
Horner's power output over the final 4km will be very similar to that of Contador and Schleck, because of the constant time-gap between them. There is some error thanks to drafting, wind and so forth, but we're talking small differences. From the graph, Horner rode the final 4km at about 350W, and so Contador and Schleck finished the climb in this range of between 350W and 360W - 5.5W/kg to 5.7W/kg
So 6.4W/kg vs 5.9 W/kg? Ferrari's numbers demand scrutiny, because they're so different.
Look at the SRM for the real values
And to find an answer, let's take the guesswork out of this and look at the SRM data - this way, we don't have to assume the length, the vertical gain in height, or the gradient of the climb.
So, for Chris Horner over the final 9.3 km (since this is what Ferrari claims is 6.42 W/kg (graph can be seen in yesterday's post):
Distance = 9.3 km
Gain in height = 736 m
Gradient = 7.91%
Time taken = 28:36
VAM = 1544 m/hour
Estimated power output = 5.53 W/kg
Of interest here is that the SRM gives Horner's power output over this interval as 348 W, or 5.4W/kg. The VAM thus overestimates the power on this climb, and this is telling (bear in mind that if you have a following wind, you'll overestimate, whereas a headwind will produce an underestimate when using VAM - this is one of its 'flaws', and the reason why the SRM is the ultimate source of "truth", notwithstanding issues of calibration)
Now, let's look at Contador and Schleck over exactly the same 9.3km interval. Remember that they all started this part of the climb together, with Schleck's attack creating the time gaps.
So, the stats are the same as above, with the exception of the time. Horner concedes 1:46, and so therefore Schleck and Contador do the 9.3km in 26:50.
Now, VAM = 1646 m/hour
Climbing power output = 5.90 W/kg.
Not 6.42 W/kg.
The only way to explain this discrepancy is if the climb has been mapped differently, so that Ferrari's gradient and the vertical change in height over the final 9km are completely different. Which is reality? You have to believe the SRM. Also, given that Horner is riding at 5.4W/kg, is it feasible that he "only" concedes 1:46 to guys supposedly riding a full 1 W/kg faster? No, it's not, and so Contador and Schleck cannot have been at that power output. And therefore, all Ferrari's assumptions and resultant calculations are doubtful.
The tactical battle - two ways to explain the racing
One final point about what Ferrari writes in that piece:
"the heat influenced the development of the TdF 2010, making the riding all the more demanding and hard, forcing the riders to measure out energies carefully, growing thinner and thinner every passing stage...None among the favorites dared to attack far from the finish, especially on the mountains, just as no team was really capable to make the race hard and selective in the first phases of the stages. "
Ferrari's observation can just as easily be explained by a reduction in the ability of riders to recover from one maximal effort to the next. We know that doping improves this ability enormously - it improves the ability to sustain high power outputs and relative intensities for longer, and it enables repeat bouts at higher intensities.
Therefore, some of the hypotheses around a "cleaner" Tour would be that:
The same rider will not attack every day. The "cost" of attack prevents this.
A single team with the identical cast of characters will not be able to dictate the tempo on the entire climb every day, and their ability to ride up more than 50% of the climb will be reduced (remember the days of three or four men from one team reaching halfway up a climb?)
When attacks are made, they have to be delayed, because the physiological/energy cost of attacking early and then sustaining 6 W/kg or higher for 40 minutes is excessive
The attacks themselves will be 'muted', at a lower power output.
I would argue that all three have happened, and not just in this Tour, but in the last two or three years, and in other 3-week races like this year's Giro. It's not only the 5% to 10% reduction in power that is telling, it's the way races have evolved. Look at Andy Schleck on the final climb - his hand was forced by the race situation - he had to attack early (9km to go is still later than some attacks back in the 90s and 2000s), and for his efforts, he and Contador paid so much that the chase group held them over the final 5km. Their maximum effort was not sustainable. And that's expected of physiology. Doping, on the other hand, would allow it.
So the point is that Ferrari has blamed the heat, but there is another possibility, which must be acknowledged. And sure, it's been hot. I would argue that France in summer is always hot, and some basic thermophysiology is that heat is far less an issue on the bike than in running. It's important, yes, but the thermal load produced by a temperature that is say 1 to 2 degrees higher than normal is not sufficient to produce these changes.
I believe the more likely explanation is linked to what we (and NY Times, New Scientist and even Jonathan Vaughters) have pointed out, that performance suppression indicates a cleaner Tour. Ferrari may have a different take, but then he did once suggest EPO was as dangerous as orange juice...
Enjoy the time-trial later!
Ross
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Posted by Ross Tucker and Jonathan Dugas on 7/24/2010 02:11:00 PM 44 Comments
Labels: Cycling
Friday, July 23, 2010
Power from the Tourmalet - 6W/kg anyone?
6W/kg? Barely. Power output data from the Col du Tourmalet
Yesterday saw the big showdown of the Tour on its final climb. Two great climbers in Alberto Contador and Andy Schleck rode man-on-man up one of the most famed climbs of cycling, in thick mist, in a battle that many felt would decide the yellow-jersey. In the end, it won't, with a time-trial to go and two riders who were inseparable on the climbs. But it was an epic day, and produced some epic performance.
So, to continue our analysis of the power outputs in the Tour, here are some insights, gleaned from Chris Horner, Chris Anke Sorensen and some self-timing of the climb (once again, power output files courtesy SRM and Training peaks)
The Tourmalet dissected. First, some estimates...
To wet the appetite, some interesting estimates of power output emerged yesterday. First, for a really methodical, and I believe quite accurate method of ESTIMATING the power outputs, check out Cozybeehive, where Ron has analysed the climb segment by segment.
This method of estimating the power output relies on using the rate of vertical ascension, or VAM, which can be calculated if you know the distance and the gradient of the climb. And herein lies a problem - there are many discrepancies in how these climbs are 'mapped', and this affects the value you calculate. Also, wind, drafting and changes in the grade also affect the final estimated power output. There's been some pretty strong criticism of it, but so far, comparing the estimates to the actual SRM data has produced quite similar values, rarely different by more than 0.2W/kg.
On the note of distance, yesterday, the 18.6km to go banner for the start of the climb was almost certainly in the wrong place. It took the peloton a full 4:42 to ride from the 20km banner to the 18.6km banner (speed of 18km/h), and that was before the climb. Once on the climb, the first 3.6km took six minutes, a speed of 36km/h. In otherwords, if you believe the banners, then you believe that the speed doubled once the climb began. I don't, and so my conclusion is that the banner for the start of the climb was late by about a kilometer (this is further seen in the on-screen TV distances, which aren't always accurate, but they said 17.6km to go - I believe this).
So anyway, the point is that what you calculate varies quite a bit as a result of this.
Ron has estimated that the power of Schleck and Contador over the final 8km was 6.0 W/kg. I think this is close, but likely a small overestimate, because of drafting effects.
My overall estimation is that they took 49:08 to climb what I believe to be the final 17.6km at a gradient of 7.6%. This gives a VAM of 1,633 m/hour, and a relative power output of 5.9 W/kg.
These are of course estimates, not measurements, and if we want answers, then we need measurement. And for that, we look to Sorensen and Horner...
SRM data from the climb
The graph below shows Chris Anke Sorensen's power from the start of the final climb. If you recall, Sorensen set the climb up with an incredibly hard pull over the first 15 or so minutes.
So a massive pull - 415 W or 6.6W/kg, for 11:12, before Sorensen's day was up, and he dropped down to closer to 310W for the rest of the climb (also, note that the speed ranged between 20 and 25km/h, not 36km/h, which further suggests that the climb was marked incorrectly for TV purposes).
Once done, Sorensen settled down to complete the climb in just outside an hour, for an overall average power output of 330 W (5.2W/kg)
Chris Horner - a barometer for the yellow jersey
Even more interesting is Chris Horner, who had a tremendous day, climbing with the very best in the world. He was part of the chase group, dropped by Schleck and Contador, but who provide for a really useful barometer, because:
The eventual time gaps were relatively small - 1:45 in 50 minutes - which means that while we can't know the power output of the leaders, but it's not too much of a stretch to infer, and
The gap between Horner and the leaders remained relatively constant over the final 5 km of the climb. When Schleck attacked, the time gap grew relatively quickly to one minute, but then it edged up to 1:30, before actually staying in the range of 1:35 from 4km to go until the finish line. Therefore, it's useful because Horner's power output in the final 5km will be very similar to what was produced at the front of the race.
So, here is Horner's graph:
SRM have divided the climb in half, with the separation conveniently co-inciding with Andy Schleck's attack. Here's a breakdown:
Average power output for the first half of the climb - 377 W, at 5.9W/kg
Note the first portion of the climb, which co-incides with Sorensen's pull on the front, which we saw previously produced 6.6W/kg. You'll see that Horner rode in the range of 390 to 400W over this period, or ± 6.3W/kg. Horner's mass is 64kg, compared to Sorensen at 63kg, so the values are comparable. The reason it's lower is the slight benefit of shelter in the group, whereas Sorensen was at the front of the race
After the attack came, Horner completed the climb at 348 W (5.4W/kg).
Note once again, that Horner's power output over the final 4km will be very similar to that of Contador and Schleck, because of the constant time-gap between them. There is some error thanks to drafting, wind and so forth, but we're talking small differences. From the graph, Horner rode the final 4km at about 350W, and so Contador and Schleck finished the climb in this range of between 350W and 360W - 5.5W/kg to 5.7W/kg
Horner's overall average power output on the climb was 360 W, or 5.6W/kg. Interestingly, if you use the VAM method for Horner, you calculate a power output of 5.7 W/kg. Therefore, I am quite confident in saying that Contador and Schleck probably averaged 5.9W/kg over the entire climb.
So, a fascinating graph and insight into the Tour's big day. But what does it all mean?
The physiological implications of the climb
Before the Tour began, there was a great deal of debate about what the performances tell about physiology. I suggested that the power outputs of the 90s and 2000s, where these climbs were frequently done at 6.2, 6.3 and even 6.7W/kg, were a sign of doping. You may recall the notion, developed by Dr Ferrari and communicated by Armstrong in his book, that they aimed for 6.7W/kg as a threshold climbing output.
Nobody has managed to achieve even 6.2W/kg for any length of time in this Tour de France, let alone 6.7W/kg. Unless I am missing something. 6.6W/kg for 11 minutes, yes, but that rider then dropped to 5W/kg for the rest. In days gone by, that was the tempo the whole way (Incidentally, you can play around with this and work out how far ahead a guy would be if he did ride at 6.7W/kg - I estimate close to 3:00 on the climb. Contador and Schleck, dropped by 3 minutes....?)
And the top two climbers yesterday arguably rode at around 6.0 to 6.2W/kg for the first half of the climb, but their power output dropped off in the second half (which we know, because the time gaps ceased to grow over someone who was producing 5.5W/kg).
What is the physiology of riding at 6W/kg? If a cyclist has an efficiency of 24%, then the VO2 at 6W/kg is about 71 ml/kg/min. If this represents 85% of a maximum, then a VO2max of 83 ml/kg/min is estimated. If the efficiency is 23% (measured by Coyle for Armstrong in 1999), incidentally, then the VO2 is 74ml/kg/min and the estimated max would be 87 ml/kg/min. Neither jumps out as not-seen-before-physiology. But, if you go up to 6.2W or 6.3W/kg, then it starts to become, well, questionable.
Horner, incidentally, riding at 5.6 W/kg, would have an estimated VO2 of 66 ml/kg/min.
Conclusion
All told, then, I interpret the figures to be a good indication of the state of the sport. Whether you want to:
Base this on the physiology (which is only part of it, but I believe an important part), or
Compare the climbing times (most of which are 5 to 10% slower than before), or
Compare the estimates of power output this year to previous years (again, they're consistently 5 to 10% down), you arrive at the same point - it's a slower Tour.
Now, tactics are of course important. Many of you have argued this, and of course you're correct. Race situation dictates who attacks, when they attack and how they ride. That's why you need many climbs, and not a single one, to reach a correct conclusion.
One Tour provides many climbs, and I think there's still huge value in this year's numbers. However, because it's still a small number, this is a hypothesis, not a finding - what would be fantastic would be to track these stats over the next ten years, and compare the 90s to the 2000s to the 2010s. And also, to look at averages for top 10, top 50, top 100, to get an idea of depth.
Yesterday, on the Tourmalet, there were tactics - ride as hard as possible. 6.6W/kg from the bottom, followed by an attack, and I don't see any signs of 'hedging' of physiology on the day. It was as hard as was possible at that stage in the Tour, and I would continue, then, to hypothesize that the more stringent doping controls, the biopassport and the scrutiny on the sport have helped bring it down.
Call it "physiologically believable" (which many don't like, but I use it with its obvious intention), or call it signs of change, I do believe that the Tour is slower, and that the days of 6.3W/kg for 40 minutes are now the stuff of highlights and commemorative DVDs.
A massive time-trial to come, where the Tour will be decided!
Enjoy it!
Ross
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Posted by Ross Tucker and Jonathan Dugas on 7/23/2010 11:31:00 AM 52 Comments
Labels: Cycling
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Jonathan & Ross
Who are the Sports Scientists?
Ross Tucker and Jonathan Dugas completed their Ph.D.'s in 2006 in the Exercise Science and Sports Medicine Research Unit at the University of Cape Town.
Ross Tucker, PhD
Current residence: Cape Town, South Africa
Employment: Self-employed. Consulting, including SA Rugby, SA Sevens, private. Strategy for high performance sports science and management and marketing
Research interests: Exercise performance, fatigue and pacing - how the brain regulates performance
Sports interests: Running, cycling, tennis, rugby, swimming, cricket, rowing
Jonathan Dugas, PhD
Current residence: Chicago, USA
Employment: Clinical Assistant Professor in the Department of Kinesiology and Nutrition at the University of Illinois at Chicago
Research interests: Temperature regulation and exercise performance, with a special emphasis on how fluid ingestion affects those two things.
Sports interests: Cycling, running, triathlon, endurance sport
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