Incremental Power Measurement

Discussion in 'Power Training' started by Die fietsryer, Mar 5, 2006.

  1. Die fietsryer

    Die fietsryer New Member

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    Obviously a 1000W effort of say 1 min. has a far greater physiological effort than a 100W for 10 mins. If working with TRIMP type formulae, they both however give the same value of x x 1000W min.



    The Maximal Power Curve (MPC), shows however that 100W can be maintained for only a fraction of the time 1000W can be maintained.



    Is there any method available that measures the mean power for whatever interval the measuring device is set, multiplies that value with a MPC factor and sums all the values to give a representative way to compare two training sessions?



    If, for example the MPC gives the time that 100W can be maintained as say
    1000 mins., 200W as say 200 mins., 500W as say 10 mins. and 1000W as say 1 min. then sprint repeat sessions of say 10 reps @ 1000W for 1 min. each should be
    10 x a 500W 10 min. sessions (because 100W for 1 min. = 500W for 10 min.).



    Averaging out over full sessions is far too inaccurate and if the power measurement device can measure every 1 second, why not value each of those 1 second values?
     
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  2. beerco

    beerco New Member

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    Yes, see here: http://www.cyclingpeakssoftware.com/defined.html
     
  3. dome

    dome New Member

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    The link does not really give any information.

    What is the algorithm that is used to calculate Normalized Power?
     
  4. sidewind

    sidewind New Member

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    Algorithm goes:
    -take power samples
    -rase those power samples to 4th power
    -take average of those 4th power power samples
    -take 4th root of the average of 4th power power samples
    -this is the normalized power

    Example:
    You have been riding
    4 minutes with 250 W and
    6 minutes by 300 W

    Average power is (4*250 + 6*300)/(4+6) = 280 W

    Normalised power:
    250^4 = 3 906 000 000 = (a)
    300^4 = 8 100 000 000 = (b)

    Average of (a) and (b) = (4*a + 6*b) / 10 = 6 422 000 000 = (c)

    4th root of (c) = 283 W
    and this is the normalized power.
     
  5. acoggan

    acoggan Member

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  6. dome

    dome New Member

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    Thank you sidewind.

    Does this mean that the algorithm assumes that the MPC has a function of Power proportional to the inverse of Time to the power of 4?

    What fietsryer is looking for is a measure of a training session relative to what the MPC shows is possible.
    So, if we call the points on the MPC, say, Maximum Power Time Units (MPTU's), then in fietsryer's post 1000 mins @ 100W = 1MPTU ; 200 mins @ 200W = 1MPTU ; 10 mins @ 500W = 1MPTU ; and 1 min @ 1000W = 1MPTU. (And for any power output there is a corresponding time that that power can be maintained for.)
    So, if the power measurement increment is 1 second, and at the end of a session we measured, say, 2000 seconds @ 100W, 500 seconds @ 200W, 200 seconds @ 500W, and 50 seconds @ 100W, then our total MPTU's would be 2000 seconds/1000 mins + 500 seconds/200 mins + 200 seconds/10 mins + 50 seconds/1 min = 1.24 MPTU's.
    This does seem a much better way to compare training sessions.
     
  7. acoggan

    acoggan Member

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    -smooth power samples using a 30 s rolling average

     
  8. sidewind

    sidewind New Member

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    The TSS (Training Stress Score) calculation principles are defined on those pages already linked in this thread, I suppose. In TSS, one hour ride on the FTP level is defined as 100, and other powers and times are compared against FTP.

    However, it should be noted that e.g. short intervals like 1000 Watts for 2 seconds are consuming other energy sources than 250 Watt ride of two hours. So at least I don't see why very different training types should be compared against each other at all. rather compare intervals to earlier intervals, and TTs to earlier TTs.
     
  9. yzfrr11

    yzfrr11 New Member

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    this is non-sense - i fear that anyone who reads this post will have a lower I.Q. as a result
     
  10. frenchyge

    frenchyge New Member

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    Uh oh, 1.24 MPTU's. That means we accidentally exceeded the MPC by 24% somewhere along the way. I guess our training is working, but now do we calculate our MPTU's based on the 'old' MPC curve, or the new one that we just created on this ride? And if our MPTU's are being referenced to a constantly changing MPC, then how do we compare one ride to the next? Oh dear, now I'm all confused. :confused:

    I guess I'll just stick to TSS. :)
     
  11. dome

    dome New Member

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    How long does it take to recover from a MPC effort? Is is unrealistic to think that short duration sprints up to MPC level can be repeated in one training session?

    TSS does average the training effort quite drastically, and if you have measurements of your effort every second or so, why not utilize that information by comparing each increment with a known performance measure such as MPC?
     
  12. acoggan

    acoggan Member

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    Because, quite simply, powermeters are capable of recording changes in power output far more rapidly than to which our bodies can respond. For example, I can pedal for 15 s at 500 W followed by 15 s at 50 W repeatedly for 20 min, and my respiratory, cardiovascular, neurohormonal, metabolic, and perceptual responses will be very similar to those resulting from pedalling steadily at 275 W - all that really varies are the motor units called upon to perform the task. However, stretch the on period just ever so slightly (e.g., to 20 s), and the situation will be quite different. To have any merit at all, any system for "scoring" a powermeter file must explicitly recognize this aspect of physiology - which normalized power, from which TSS is calculated, does, by applying a 30 s rolling average to the raw data before performing any further calculations.
     
  13. frenchyge

    frenchyge New Member

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    Depends on where on the curve you're trying to hit. A 30sec - 1min max effort can be recovered from within 10 mins, but a 2hr max effort may take a day or two. That alone illustrates why hitting the MPC curve at 1 minute should not produce an equal number of MPTU's as hitting it at 2 hours. How could you possibly compare the two 1.0 MPTU rides?

    You really should consider reading through http://www.cyclingpeakssoftware.com...ningChapter.pdf , which gives a great explanation of the physiological factors involved and how they relate to the development of Andy Coggan's Training Stress Score (TSS) system.
     
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