Polar 720 Power Pedaling Index

Discussion in 'Cycling Equipment' started by HarryS, Jan 22, 2004.

  1. HarryS

    HarryS New Member

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    I dont want to get into any discussions as to whether this unit is good or not. I happen to have one installed and it seems to be working quite well. Instead, I am calling on those amongst you who have the same unit and have some more experience with it. The Polar power option gives you a value called the pedaling index which ranges from 0-100. Presumably 100 represents a perfect motion of the crank, hence the lower the number the worse your pedaling. How high should a decent PI be on this unit and if it is as low as mine (22) what need I do to improve it? It seems to me that one gets some instant "biofeedback" that can be used to improve ones pedal motion. If that is the case, let me know how to use it to my advantage. Thank you!
     
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  2. peterwright

    peterwright New Member

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    I also found my PI to be around 20% when I first started using it. With effort I managed to increase it to 30%. I have not seen or spoken to any rider who consistently gets over 40-50% so am not sure how realistic it is to expect that. I certainly think that one legged drills and roller training help and recently I have been riding powercranks to improve my stroke.

    Hope this helps.

    Peter
     
  3. HarryS

    HarryS New Member

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    Thanks Peter:
    Let me ask you a couple more question.
    As you were increasing the PI value, how did you go about it? Did you leave it up on display and just tried to alter your stroked gradually to improve this number. If so, was it more the scarping in the 6o'clock position or the pulling over the top 12'o clock osition that mattered? Since you increased the PI did you notice any improvements in your performance or the preceived effort?
    Thanks
    Harry
     
  4. peterwright

    peterwright New Member

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    Thats a tough question...
    I did leave it on at the top of my display all the time and tried to focus on my pedal stroke on all my morning training rides. I tend to concentrate on the pulling up of the leg with the hip flexors more than anything else.
    I have certainly noticed an improvement in my performance since using the Powercranks, as they are a tool that immediately lets you know if you are not pulling up and over. This may be down to the fact that my training has become more focused or down to the pedal stroke improvements.

    Good luck.

    Peter
     
  5. dkxkvtr

    dkxkvtr New Member

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    The polar meter compares 1/3 of the pedal stroke (from 1 to 5 o'clock) to the total pedaling cycle. the reading you get is actually 1/3 the total cycle. If you were getting 20% with the polar that is the equivalent of 60% on a computrainer. The polar monitor is accurate. Ive compared it simultaneously to the computrainer.
     
  6. cycleak

    cycleak New Member

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    HarryS:
    I've read all the reviews and comments on this powermeter and am still interested in getting one. Do you use it on the trainer much and if so, how well does it seem to work?
     
  7. dkxkvtr

    dkxkvtr New Member

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    I would definately recommend the polar meter!! Obviously, if finances are not a consideration it should not be your first choice but the polar meter is very very adequate. Ive compared it simultaneously to the computrainer and they are amazingly similar.

    I use my polar meter on the trainer and it works very well although you realize you cant compare power numbers "on the road" to power numbers on the trainer. They are two different animals. The readings themselves are reproducible so, you always have a frame of reference.
     
  8. Mansmind

    Mansmind New Member

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    Pedaling Index


    My average PI falls right at 24%, with the maximum I've ever had being in the 65% range (forget the exact number). I've played around with different pedaling styles if for no other reason than to see what affects the number. Overall, I'm not sure I think that it's a very useful measurement. What I've found is that to increase the index, I in effect have to decrease the force applied on the down stroke in order to keep the overall stroke more consistent with respect to force. This doesn't seem advantageous to me as I believe that no normal human will ever be strong enough either on the pulling part of the stroke, or the cross-over strokes, to be able to apply "natural" force on the down stroke while maintaining consistency throughout. There are many times, expecially when hammering up a hill (which I have a lot of around here) that the index is reading as low as 11%.

    Power Unit
    You'll find a lot of posts on this forum regarding the accuracy/inaccuracy of the polar power meter. I've done several studies personally both with regard to the accuracy, as well as to set-up on the bike to see what affects the reading and/or how to make it more consistent.

    In short, I agree with the other poster, I've been very happy with the meter, and am convinced that it's accurate within tolerable limits, especially if you're trying to track improvement rather than absolute power values. In either case of use however, I believe the meter to be very useful.

    Regarding the difficulty of using it on a trainer, there IS some issue here. The vibration created by a trainer definite affect on the power readout (I suspect by affect the chain tension sensor). What I've found through tests however, is that this affect seems to be concentrated around certain frequencies.

    FWIW, it seems that on MY trainer anyway, the vibration starts to have a detrimental effect at wheel speeds equal to 28-30 mph and up.

    What I've done to deal with the issue is to increase the resistance on the trainer dramatically (almost maxed out). This in turn allows me to generate x power at much lower wheel speeds. The lower wheel speeds create less and/or a different frequency vibration. As a result of doing this, I get the same consistency, and very good correlation with road results (which was an added benefit.

    As an example, (and you can verify this using tools at analyticcycling.com, powertap meters, etc. )

    It takes a considerable amount of power to maintain a speed of 16 mph on a 3% grade (as opposed to flat road). The actual power dependant upon weight, air resistance, rolling resistance, etc. For me, that number falls into the ~290 watt range. Not only are these the numbers I get while riding on the road, these are also very close to the numbers I get while generating the same speed on a trainer. In addition to that, I've found that my heart rate (YES, I KNOW IT CAN VARY WITH CONDITIONS) to be very close in either situation. Perceived effort is close enough that I can't tell the difference. The power reading in this test isn't affected by more than 5-8 watts regardless of what gear I use to generate the power.

    Considering all that, I believe I've found at least ONE way, or at least one riding conditioning in which not only are the results repeatable, they also correlate very well with road riding conditions. Being that I've increased the resistance on the trainer, I've yet to do any testing at much greater wheel speeds (greater than 30 mph) since that requires greater power than I generally exercise at on a trainer.

    I HAVE however, generated increasing speeds a few times (since adjusting) just to see the affect on the power reading. What I see is essentially what I saw before. At some point in the 30 mph area, the vibration reaches a frequency at which the readings become relatively inconsistent, and at a speed just a little faster, the readings start DECREASING. Strangely enough, this seems to correlate with the vibration you feel on a trainer (mine actually feels to smooth out at the same time).

    If anyone else has similar results and/or has tried similar things, I'd love to hear about them.

    John
     
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