Power and Chris Froome
Submitted by Nick on Mon, 07/27/2015  20:24
The Tour is over for another year and if you’ve caught even a scrap of it you will have heard or read something about power. If you are more of a casual observer of bicycle racing – and only sign up for three weeks of sleep deprivation in July – you might wonder what the hell they talking about. Power? Port Power? Cold Power? Then there are all the terms and acronyms being used. FTP, CP, NP, W/kg. Coupled with no definition of these in the articles (which are bound to kick off once the dust settles on Froome’s win) the ‘you’re losing me’ point hits fast.
No more. Here is a quick reference guide for anyone looking to both wrap their head around the power ‘lingo’ and a little more food for thought in relation to Chris Froome and his ‘controversial’ heart rate. But first, the basics:

Power meter: a device that measures the effort a rider is applying to propel their bicycle. It is measured in watts. Below is an example of the type I use (crank based). They can also be in the pedal or the rear hub.

Power: energy value, expressed in watts, being produced by a rider. And in case you’re wondering if it’s the same watts that your energy company provides, Robert grabbed a toaster to prove that it is.

Average power (AP): is the average wattage held throughout an entire ride.

Normalised power (NP): as races can include lulls where there is no pedalling, it is possible to have two rides with the same average power however with one being significantly harder than the other. NP is therefore an estimate of the power a rider could have maintained for the same physiological “cost” if your power output had been constant. In these cases it is more reflective of ride intensity than AP.

Functional threshold power (FTP): is the quasi steadystate power that a rider can (theoretically) hold for 60 minutes. Common calculation of this is taking between 9297% of a 20 minute power test.

Power to weight (w/kg): looking at power as an absolute number does not give the whole picture, as a heavier rider can produce more watts than one who is lighter. Dividing power by a rider’s weight gives a more in depth understanding. Especially as riding up any gradient over roughly 3% a rider’s w/kg becomes a bigger predictor of speed than raw power alone. It is this ratio that is central to the debate around Chris Froome – both his ‘stolen’ data and that which he released.

VAM: coined by the (now shunned) Italian doctor Michele Ferrari. It stands for velocità ascensionale media which translated means ‘average ascent speed’ and is expressed in metres per hour.

W’: bit of a curly acronym that represents anaerobic work capacity (used in short, sharp sprint type efforts). I wouldn’t get too caught up with it. But when articles drop it in it can lead to a fair bit of head scratching.

kJ: the energy cost of a ride. You can read Jose’s more in depth method of calculation here, otherwise the shortcut method is taking that value as ‘calories’ and multiplying it by 4.2 to get a kilojoule cost for a ride. Great way to get an appreciation for how much energy the Tour riders burn each day. When you consider a slice of pizza is worth about 1500 kJ a stage like this is worth nearly two medium size!
The second part is an attempt to give a little more context to Chris Froome’s official (and unofficial) data. Last year Svein Tuft was generous enough to share his ride data from stage 10 of the Tour. I wrote it up for RIDE Cycling Review 65. And without looking to rehash the article (you can still grab a copy here) there are some striking takeaway points. Namely the time Tuft – a 74kg domestique, not a climber – spent over 5 w/kg and the heart rate he held during those efforts; all seen below.
Now given I don’t work at the UCI or have access to biopassport information of any rider, I’m assuming ‘innocent until proven guilty’ for all athletes. The point of publishing this is to just provide a counter point to many of those implying the low ‘maximal’ heart rate of Froome’s was due to factors outside of what should occur naturally. Here is another rider, with polar opposite race goals and build to Chris Froome, with a heart rate not very dissimilar to the Sky rider.
Svein’s whole ride includes the ride to and from the start and finish lines, so total average and normalised power and average heart rate are not totally reflective of that over the entire stage. Still, his splits up the Col du Firstplan, Petit Ballon and other climbs of the day are segmented in to the laps. He was close to maximum (and over 5 w/kg) over the first two climbs – with average heart rates of 157 and 159. And only 5% spent over 169 and 163.
Point being, now armed and ready with a much better understanding of power and data figures it’s still far too simplistic to go looking at a riders figures in isolation. Or claiming a rider’s threshold heart rate is too low and an anomaly (as was levelled at Froome) – when in fact others exist with a similar cardiac output.
If this year is anything to go by, live rider telemetry is not far off being a reality. And I fully expect, for certain riders, that it will include power. So having an understanding of it will certainly add to the experience as a fan  just know there will always be more questions than answers. And the answer to questions you cannot answer should not default to “doping”. Because as we have seen there is always more to a rider who seems ‘not normal’  and in nearly all cases it has a legitmate explanation.
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