Volatile Power Readings

Discussion in 'Power Training' started by t17ood, Jun 1, 2015.

  1. t17ood

    t17ood New Member

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    Hi,

    I have been training with HR zones and recently decided to take the plunge and buy a power meter (stages).

    I completed a lab test two months ago and have been using the figures with my HR and thought it would be a simple job of switching to the power figures and carry on training; however, when I ride with my power zones, the figures jump about with so much volatility they are of no use at all.

    On my first workout, the high and low power alarms were going off back to back continually for the first 20 mins before I had enough and had to switch them off.

    Is there something wrong with the meter or head end or am I doing something wrong? I have tried looking at the 10s and 30s figures instead but even these seem to jump around a bit much.

    I have naturally got quite a smooth pedaling action, which was confirmed at my lab test so I don't think this is the issue.

    Any insight you could provide would be greatly appreciated.
     
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  2. An old Guy

    An old Guy Member

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    You might give a bit more information.

    What type of meter are you using? And what type of display?

    How much do the numbers vary?

    Are you on the road or on a trainer?

    What type of terrain?

    What time frame?


    Smooth pedaling has nothing to do with smooth power. A change in wind or gradient will have a large change in power.


    You might learn to hold your power more constant. You might not. I don't think it is that important.
     
  3. t17ood

    t17ood New Member

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    Meter is Stages on a DA 900 crank
    Head unit is a Garmin 500
    When I started off I just had the power zone on display (not instantaneous) and it was varying from zone 1 to zone 5 and back within a second - this continued for about 20 mins before I had to turn the alarms off.
    On the road on pan flat terrain but in a strong gusty wind.

    I am 44 years old and have been racing on and off (more off than on) since I was 16. I am an ex Cat 1 road/track rider now just focused on Cyclocross.

    I guess I just need to know if what I am experiencing is normal or Is it common that people who use power meters are able to hold the power within a power zone?
     
  4. RapDaddyo

    RapDaddyo Active Member

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    Power, as measured by strain gauges, is inherently volatile, much more volatile than any other metric that has been available to you until now (e.g., HR, speed, cadence). This is in part due to the strain gauge measurement frequency versus your cadence. You may have a smooth-as-silk pedaling stroke, but you nonetheless generate virtually all of your power in a very narrow range just before and just after halfway from top dead center to bottom dead center with each leg. So, if your power meter measurement frequency is not precisely matched with your cadence, you will get volatility induced by this mismatched frequency (aka precession).

    My suggestion is to set your power meter handlebar computer (Garmin 500) to display a rolling average of watts. I use a 5sec average, but most PM computers provide for several options. Your ride file will still capture your power data at the higher frequency (e.g., 1sec), but your Garmin will display the rolling average.
     
    dkrenik likes this.
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