Je n'avais fait qu'un seul calcul sur la base des 15 derniers km de Schleck/Contador dans le Tourmalet et j'obtenais effectivement bien moins que le Dr Ferrari et bien plus proche de Ross.pierre-yves a écrit :http://www.sportsscientists.com/2010/07 ... f+Sport%29
Voir ci-dessous la critique de l'analyse de Ferrari.
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
Sauf si la retransmission télé fut plus courte que la réalité (ça peut arriver), j'ai chronométré en 43'03 les 15 derniers km pour 1172m de D+ (donc 1633 de VMAscensionelle) et une puissance nécessaire (ne pas oublier dans le calcul l'altitude et la température* qui économise quelques watts ainsi qu'une ligne de chaîne bien meilleure que la nôtre quand on monte tout à gauche
) de l'ordre de 6-6,1 W/kg, ce qui est cohérent avec les 5,9 de Ross calculés après la longue attaque de Schleck.*il y a, aux puissances qui sont les leurs, un petit 10w de différence entre une ascension par 10°C au niveau de la mer et la même par 20° à 1500m d'altitude.
Nick
