A question for the power gurus

The Kennington Kaiser

I'm stepping out tentatively into the world of training with a power meter and having got one at xmas and now putting it good use. I've read a bit of Ric's (Stern) blog and am starting to try and get my head round the various bits of data and how to interpret it.

In order to establish my functional threshold power I did a twenty-minute flat out time-trial yesterday and an average power figure of 351W was the result. This was done with the zero averaging off so that the meter only measured my power when pedalling and didn't average down for the 30-40 secs or so when I stopped pedalling halfway through the test.

Then I started to get a bit confused - when I ran the data through Training Peaks software it told me that the average power for the ride was 338W and that my Normalised Power was 360W. My rather long winded question is: what figure should I be using as my FTP and the subsequent level of training that follows?

I'm sure that there is a very simple answer to this, but I'm struggling to find it.

Thanks in advance

jibberjim

For a test as short as 20 minutes, you really want to find something without a break - for an hour 30 seconds of not pedalling throughout will not make a huge amount of difference to your power (the few watts will be within the accuracy of your power meter and still get you within the 5 or so watt ballpark) But for just 20 minutes as you saw just a short time not applying the power at junctions or when you come up to a car or whatever can make a big difference.

338 AP vs 360 NP for a 20 minute test is too varied too - it's not long enough for the NP algorithm to be reliable but you didn't ride it steady so it's likely you could've got a different AP riding steady.

I'm afraid the simple answer is to do another test - a better one.

Alex_Simmons/RST

The software is reporting average power (including zeros) as it should.

Suggest turning on the zeros in the average power reading on the meter. Non-zero averaging is pretty meaningless since time spent not pedaling affects your ability to produce power when you do pedal again.

Don't worry too much about it not being a perfect test. First attempts are never perfect. You'll get better at it over time.

We know that your 20-min average was 338W and since NP was 106% of AP you rode at times much harder than average and other times much less than that (i.e. your time coasting).

Had you ridden without interruption and paced a little more evenly, then it's likely you could have averaged higher than 338W

Typically I see the ratio of FTP (1-hour power) to 20-min maximal average power in a range of 90-95%. So given the above, I'd suggest a starting estimate of FTP of ~ 320W. It won't be hideously wrong, and as you refine your testing and gather more data from training and racing, so too do you refine your FTP estimate.

Here are a couple of items on it:
http://alex-cycle.blogspot.com/2008/05/ ... -sins.html
http://alex-cycle.blogspot.com/2009/07/ ... ftp-2.html

The Kennington Kaiser

alex and jim- thanks for the comments, they're helpful and encouraging. I know it wasn't as consistent and steady an effort as I'd have wanted but without a turbo trainer and in the part of the world I live it's pretty difficult to replicate a steady, uninterrupted TT effort.

I'll use ~320W as a ball park FTP and might give it another go over a longer time period in the next fortnight. Alex, I've read the posts in the two links so it;s starting to make a bit more sense now. Still rather like learning a new language and science though.

Thanks again.