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  • Marc

    Another article about power and how hard a ride was, without mentioning heart rate even once. If you don’t include heart rate, it’s very hard to take you seriously. If you’re on a bad day, e.g. when you’re not fully recovered from a ride the day before, an average or normalised wattage of 200 might be a very hard ride. While that same wattage might count as an easy ride when fully recovered. I’ve seen many cyclists make the mistake of going for an ‘easy’ ride and then pushing their bodies way too far, just because 200 watts is supposed to be easy. In my opinion it is more important to look at your body and keep an eye on how fatigued it is, very easy to do by looking at your heart rate, than it is to look at how hard a ride is supposed to be because the wattage says so.

    • Mark

      Explaining what normalised power is has nothing to do with heart rate though… Also.

      200 watts is 200 watts. Just because one day you do it when you are fatigued that doesn’t mean the ride was easier/harder you just perceived it differently.

      • Marc

        You make my point. If you perceived a ride to be harder, 99 out of 100 times it was harder on your body. So for you it was a harder ride that day. If you want to train properly/wisely the thing that matters is how hard a ride is on your body.

        • Mark

          200 watts is 200 watts just like 400w is 400w. If you are meant to do 20 minute efforts at 400w but are fatigued so do them at 300w you do not get the same adaptions as doing the effort at 400w.

          Adapting your training to your fatigue levels (which is often reflected in HR) is important but a completely different issue.

          Basically the author explained the concept of NP well and you criticised it on a tangent not relevant to the original topic.

          • Marc

            It was the author who linked normalised power to how hard a ride is, not me.

            And regarding your first sentence about adaptations, I don’t want to be rude, just give you some helpful advice: don’t apply that principle when you write your training plan.

        • Justin Evans

          A power meter gives you absolute numbers that quantify how hard a ride was on your body. It’s call ATL. Heart rate varies too muc (in most cases) to do that as accurately as a power meter.

    • Michele

      You should write your own article about Power and incorporate Heart Rates into it.

      Then we can take you seriously.

      • Marc

        When Cyclingtips asks me, I’m more than happy to do so.

    • Alex Simmons

      It’s hard to take seriously those stuck in the paradigm of HR. HR has it’s (very limited) uses but when training with power, HR is at best redundant, at worst misleading. Going too hard on an easy day is not a fault of using power or the concept of Normalized Power. It’s the fault of the rider for not going easy. You don’t need a power meter or a HR monitor to know how to ride easy. For starters, both elevated and suppressed HR response can be the result of fatigue or other factors unrelated to fatigue.

      • Wily_Quixote

        HR will correlate to power but is not a direct measure of it, so i wouldn’t say that HR is completely useless and might be a useful integration to assessing normalised power – presuming that the overall goal is to measure physiological cost of training and from that – adaptation.

        What is not clear in the article is how the normalisation is averaged. I imagine that it is an algorithm that deletes the monitoring of low efforts in the training block but, if this is the case, normalised power is an artificially high figure and really is just a measure of time spent in peak effort.

        As a caveat, I know absolutely nothing about powermeters, but; being the internet, i thought why not give an opinion.

        Edit: i see that lower down you have explained how the power is averaged.

      • Marc

        I’ve never said that power meters are useless. They certainly have their place and I believe that anyone who takes his/her cycling serious should use both power and heart rate. Just going by your power meter is a very bad way of going about your training. It’s the reason you see so many riders overtraining nowadays. They’re always chasing numbers on their power meter, don’t know how to listen to their body. Throw strava into the mix and you know why so many riders are stuck at the same level, never really improving until they hit the wall..

        • Sean

          Were riders smarter in the old days?

          • Marc

            Maybe they had less opportunity to stuff things up? I think a rider nowadays can train smarter than they did in the old days by combining the valuable stuff from the past with the useful stuff from today. Wattage does not equal heart rate. If you use both, you’ll have an advantage over riders from the old days. In my opinion anyway.

        • Alex Simmons

          Your anecdotal observation is hardly convincing that more people are “training dumb” now days compared with a time before power meters were readily available. The power meter is a tool, not a bolt on motor (thanks to Chris Mayhew for that Pithy Power Proverb). If people don’t use a tool wisely, that’s hardly the fault of the tool. NP was developed precisely to enable people to use the tool more wisely.

          • Marc

            It’s not so much anecdotal. If you only use a power meter it’s impossible to train smart. You’ll be missing essential information. A power meter doesn’t listen to your body nor provide the essential information your heart rate provides.

            • Alex Simmons

              You claim that people are dumber now because of power meters is anecdotal. As for not being able to train smart with only a power meter, that is patently false. As for HR being actionable intelligence, hardly. It’s mostly a redundant distraction and often misleading.

  • HRC-E.B.

    The interesting thing is that it might give a better indication of “how hard” a session was compared to average power, but it is still pretty far from showing the complete picture.

    It is possible to think of two rides of equal duration and same normalized power that would be dramatically different in terms of energy systems used and overall metabolic stress (and thus in terms of recovery needed, among other factors).

    For example, doing hill repeats on a short steep hill in one minute at close to one-minute-max power vs doing repeats of 5-8 minutes or longer on a longer and less steep hill.

    You might be able to achieve the same NP and TSS with both rides, but the former will be harder on the body (more nervous system and hormonal stress, taps more heavily into the anaerobic glycolysis, etc.) Different energy systems, different training effects, different longer term effects as well.

    Just saying…

  • 555

    Thanks for the explanation regarding Normalised Power. Had heard the term a lot but never researched it.

  • Lyrebird_Cycles

    I personally think this article would be more useful and easier to understand if the algorithm used to derive “normalised power” were included.

    Basically it is found using the same method as is used to find RMS power (the square root of the mean of the square of the measurements) but with an index of 4 instead of 2, so it is the fourth root of the mean of the fourth power of the measurements. To make computation easier the measurements are taken as 30 second blocks.

    • Alex Simmons

      The NP algorithm uses a rolling 30-second rolling average, not 30-second blocks. The choice of a 30 second rolling average was not for ease of computation but rather has a sound basis in physiology and was designed to reflect the time course of relevant physiological responses to changes in exercise intensity (e.g. muscular metabolic responses, blood lactate levels, cardiac output, blood hormone levels etc) which all have similar half lives of the order of about a minute.

      You can see this if for example you performed a workout consisting of micro intervals, e.g. long blocks of 10-seconds on/10-seconds recovery. The NP and AP values would be the same. The main metabolic responses would be similar to an isopower workout at the same average power, hence NP and AP would not be all that different either.

      Similarly the 4th power was chosen as it closely reflected the non-linear physiological responses to exercise intensity (power). The research up to that time indicated a power of 3.9 for BL response with increasing power but the algorithm is not particularly sensitive to the power value used and so for a little computational convenience the 4th power was chosen.

      • Lyrebird_Cycles

        Thanks for the correction Alex, you are on top of your subject as usual. I had thought that the data collection was digital and used an average over a 30 second capture window, hence the description as blocks. What you are describing corresponds to a lossy integrator with a 30 second time constant, that is more typically an analogue technique (a lossy integrator is a form of low pass filter). I must admit to being at a bit of a loss to work out what value you then raise to the fourth power, unless you are sampling the lossy integrator at intervals?

        BTW your illustration doesn’t compute: the 10 second “micro blocks” result in an AP of 0.5 x peak (obviously) whereas the NP using 30 second block averages is 0.57 x peak because (((1/3)^4 + (2/3)^4)/2)^0.25 = 0.57

        • Alex Simmons

          You must still not be using the correct method to generate a NP value then. For a signal that goes 10 seconds @ 200W then 10 seconds @ 100W then the average power will be 150W and the NP will be 150.5W (over say 30 minutes)

          i. After the first 30 seconds of data, and for each second thereafter, calculate the average power for the previous 30 seconds.
          ii. Raise each of those rolling 30-second average power values to the power of 4. Continue for 30 seconds past the last power value.
          iii. Average the values raised to the 4th power
          iv. take the 4th root of the average obtained in step iii.

          That is NP.

          • Lyrebird_Cycles

            I included my calculation in the post, it accords with your original description of microblocks: I was pointing out that your illustration didn’t compute the way your description implied that it did.

            Your update is much clearer, thanks. It also resolves the issue of which values are actually used in the NP algorithm and makes evident that it was chosen to include some noise reduction.

            • Alex Simmons

              Oh for sure, yes it is one kind of filter.

              My main point was that each of the steps used in the algorithm has a sound basis in physiology and I used the micro intervals as an example of when frequent power variation does not necessarily lead to any significant inflation of NP over AP since the physiological / metabolic responses are too slow. Once however you make those effort variations last longer, e.g. for 30 seconds or longer then you’ll see NP begin to increase relative to AP. e.g if those 200W/100W intervals were 30 seconds each then NP rises to 157W. At 60-secs for each 200W/100W interval then NP would be higher again – 164W. At 2-min for each of the 200W/100W efforts the session NP is 167W.

    • Tom Shield

      Thanks for providing this explanation, leaving this out of the article was a major omission in my opinion, given the title of the article.

  • Alex Simmons

    It might be useful also to reference Andy Coggan, who is responsible for the original concept of Normalized Power, which was first put into the public domain nearly 15 years ago in this classic Wattage forum post:
    http://lists.topica.com/lists/wattage/read/message.html?mid=907028398&sort=a&start=9350

    • Lyrebird_Cycles

      Thank you very much for that link. I’d not seen it before, it explains a great deal that was missing from the article above.

    • Spartacus

      Thanks for posting the link Alex. Coggan reads and occasionally replies to comments on here.

  • Alex Simmons

    Some additional comment, it is helpful to recognise that NP’s “validity” (in the sense of providing an indication of similar level of strain from an isopower effort) exists in the longer duration domain, that is for assessing efforts of at least 30-minutes or longer. There are couple of reasons for that, partly physiological and partly to do with the manner in which the NP algorithm is calculated. Also in general NP from a hard ride will be no more than 5% higher than quasi steady state efforts of about an hour. How much higher one can push mean maximal NP relative to mean maximal AP depends somewhat on the individual’s unique cycling phenotype.

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