Perceived Efforts...

The foundations for successful riding

Re: Perceived Efforts...

Postby Alex Simmons/RST » Mon Apr 20, 2009 12:47 pm

Deanj wrote:
toolonglegs wrote:
Ant. wrote:5s display smoothing for me.
I done an awesome MIET through some very undulating terrain without looking at my meter at all, and it is -very- isopower'ish
. I impressed myself 8)


I have no idea what you are talking about :oops:


I was playing around with settings on the powertap computer, I'd noticed in one of Ant's posts he was talking about data smoothing so I sent him a pm a few days ago asking which he had been using.

and to complete the issue:

1. on the road, power output is highly variable, and is the first thing people notice when they see it on a bike computer for the first time (or when they inspect a power meter file)

2. there is a mathematical artefact of the way the Powertap calculates data, which exacerbates the variability in the second to second data. It isn't an accuracy problem (on average). The issue is caused by the fixed duration sampling of the torque data, which results in an effect known as "aliasing". It is more noticeable at certain cadences over others. I can explain more if anyone is interested.

3. to help reduce the "signal noise", it is useful to set the display to show a rolling average power, usually something like a 5-second rolling average tends to reduce the variability in the second to second data somewhat. over time, if you are using the meter to guide say an interval effort on the trainer, then you get pretty good at doing a running integral in your head and not concern yourself with the ups and down of the more instantaneous data but rather focus on the overall effort level.
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by BNA » Mon Apr 20, 2009 3:00 pm

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Re: Perceived Efforts...

Postby toolonglegs » Mon Apr 20, 2009 3:00 pm

OK...got a better idea now...hopefully experience what you are talking about soon as well...but today it is trip to doctors...sinus has turned my head into a pumkin!.
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Re: Perceived Efforts...

Postby Deanj » Tue Apr 21, 2009 8:11 pm

Alex Simmons/RST wrote:and to complete the issue:

1. on the road, power output is highly variable, and is the first thing people notice when they see it on a bike computer for the first time (or when they inspect a power meter file)

2. there is a mathematical artefact of the way the Powertap calculates data, which exacerbates the variability in the second to second data. It isn't an accuracy problem (on average). The issue is caused by the fixed duration sampling of the torque data, which results in an effect known as "aliasing". It is more noticeable at certain cadences over others. I can explain more if anyone is interested.

3. to help reduce the "signal noise", it is useful to set the display to show a rolling average power, usually something like a 5-second rolling average tends to reduce the variability in the second to second data somewhat. over time, if you are using the meter to guide say an interval effort on the trainer, then you get pretty good at doing a running integral in your head and not concern yourself with the ups and down of the more instantaneous data but rather focus on the overall effort level.


The variability was the first thing I noticed, mainly due to the 'newness' of the power meter. Its hard to take your eyes off it the first few rides as your can't stop looking to see how much ( or little :wink: ) your putting out.

Have done about 10 rides with it now and you quickly get a feel for your efforts and start to pay less and less attention, just a quick glance. Coaching has started this week for me and did my first training ride today, only a few glances to make sure I wasn't slacking off, paying more attention to time. Avg around 235-240w for Z1 and 330-335 for the tti intervals, looking forward to seeing how things go!
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Re: Perceived Efforts...

Postby Alex Simmons/RST » Tue Apr 21, 2009 10:04 pm

Deanj wrote:Avg around 235-240w for Z1 and 330-335 for the tti intervals, looking forward to seeing how things go!

:) nice
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