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Cycling efficiency for different riders (it varies a lot)
Replies
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NorthCascades wrote: »robertw486 wrote: »I don't cycle enough to justify power meters, but likely even if I did I wouldn't buy them. In the end it most of this fitness related stuff is down to best estimates, and adjust as needed. Even if a person manages to buy very accurate meters, the gross cost still isn't an exact.
Unless they have Bill Gates money, no one buys power meters to count calories. That's not what they're for. Being able to tell you how many calories you've burned is an interesting side effect of how they work, but not worth $300+ for most people. I'm getting this weird feeling that some MFP Mythology is being created in this thread. 🙂 Power meters are a training tool, they're useful because they measure intensity in a repeatable and precise way. The data they produce has other uses including frankly astonishing calorie accuracy. Analogy: a car has lots of uses but nobody buys one to store things on the back seat. 🙂
I did a search on MFP and one of the first threads I came up with was comparing calorie counts with meters, MFP estimates, and a fitness device.
As for training aids, no doubt power meters are the best real world get out and ride aid a person can have right now. I've never questioned that at all, but since the thread went more into the human efficiency side of things just highlighted that it introduced some more error. Of course that part of the error exists with everything short of metabolic ward testing anyway, but error is error.0 -
A power meter these days has a maximum error of up to 2% but most are less than that. You can literally look up the maximum error specification for a power meter before you decide whether it's a good value or not.1
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NorthCascades wrote: »A power meter these days has a maximum error of up to 2% but most are less than that. You can literally look up the maximum error specification for a power meter before you decide whether it's a good value or not.
The accuracy of the power output is very good. And, I would argue that the repeatability may be more important a metric than the absolute accuracy in terms of it's helpfulness as a training tool.1 -
NorthCascades wrote: »A power meter these days has a maximum error of up to 2% but most are less than that. You can literally look up the maximum error specification for a power meter before you decide whether it's a good value or not.
I'll make a correction here... especially being that there was a statement about MFP mythology being created.
You can easily research manufacturers claims of accuracy, and easily test how repeatable many meters are. Though they are getting better and better, all have flaws when tested using scientific methods, and the mean accuracy is often getting within 2% or so. But all I've seen tested using any scientific method often have areas where they are less accurate, and I wouldn't even say 5% is an absolute max error. Once again, averages don't matter for absolutes.
Cadence, temps, swings as temp changes, and all the associated software logging bugs still produce error. It may well be less than 2% for certain meters, on average or expressed as a mean. But some of those tests also show variations unit to unit that are greater.
From the peer reviewed stuff I've seen personally, I'd say the manufacturers claimed accuracy rarely holds water, and it's more of a measure of repeatability as mentioned by @Jthanmyfitnesspal above. And for 99% of people that is sufficient data for most riders unless that data is grossly skewed, which seems to be rare. Most meters that stay on the market are probably within a fairly small average accuracy.
That said, still by far the most useful measure of power available to the normal person. And in all fairness, even the testing required for strict power measurements can get expensive fairly quickly. The fact that they are making available such data for the prices they are is surprising.1 -
robertw486 wrote: »From the peer reviewed stuff I've seen personally, I'd say the manufacturers claimed accuracy rarely holds water,
I wonder why false advertising lawsuits haven't put these fraudsters out of business?0 -
You can validate the accuracy of a power meter of you want to. For pedals, you hang a known weight from the spindle and make sure the torque reading is correct given your crank length. Then you count pedal revolutions for 15 seconds and multiply by 4 to make sure it's reporting cadence correctly. (Mass (kg) x gravity (9.81) x crank length (in meters) = expected torque (in Nm))
Here's a picture:
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@NorthCascades : impressive! I didn't know they reported instantaneous torque. That's useful.
To work, they they need to determine the mean torque and multiply by the angular velocity (to get power). Ideally, on both sides (I wonder how much that matters). For the versions built into the pedals, the force has to be converted to torque, which is not that easy (or accurate), since only the component perpendicular to the crank counts. Actually, it's amazing the pedal implementations are at all accurate (are they?).
And, do I need to say it again? the conversion to calories burned varies quite a lot between riders.0 -
NorthCascades wrote: »robertw486 wrote: »From the peer reviewed stuff I've seen personally, I'd say the manufacturers claimed accuracy rarely holds water,
I wonder why false advertising lawsuits haven't put these fraudsters out of business?
I can't say. Maybe because people either don't want to spend a lot of money to sue over a few hundred dollar device, the manufacturers have covered themselves with legal claims, or the people have convinced themselves that they have little or no error?
Here's a chart from an actual study, and I'm not seeing a lot of absolute 2% claims that apply to a variety of power levels and cadences....
https://jssm.org/tablejssm-17-305.xml/table001.xmlNorthCascades wrote: »You can validate the accuracy of a power meter of you want to. For pedals, you hang a known weight from the spindle and make sure the torque reading is correct given your crank length. Then you count pedal revolutions for 15 seconds and multiply by 4 to make sure it's reporting cadence correctly. (Mass (kg) x gravity (9.81) x crank length (in meters) = expected torque (in Nm))
Here's a picture:
That would simply measure static torque, and validate the crank RPM sensor. It won't measure rotational torque.Jthanmyfitnesspal wrote: »@NorthCascades : impressive! I didn't know they reported instantaneous torque. That's useful.
To work, they they need to determine the mean torque and multiply by the angular velocity (to get power). Ideally, on both sides (I wonder how much that matters). For the versions built into the pedals, the force has to be converted to torque, which is not that easy (or accurate), since only the component perpendicular to the crank counts. Actually, it's amazing the pedal implementations are at all accurate (are they?).
And, do I need to say it again? the conversion to calories burned varies quite a lot between riders.
It's for the reasons listed above that most power meters will have some error and variation. Since they are measuring snap shots of static linear force, and not true angular force, they use various algorithms to smooth the transitions and spikes, estimate torque, and then use the formula appropriate (to the power measure output) to calculate power. For a bike, much of the algorithm would be based on averages found in testing, since a human isn't as repeatable as say a car engine. For that reason the torque vector magnitude is approximated.
A "true" torque measurement would (as you stated) be perpendicular to the crank, thus measured at bottom bracket or rearward. That would also account for rotational inertia. Higher end methods of measuring torque almost always use a load cell to generate power, or through and eddy brake or similar system. Even then they are subject to certain conditions to work properly, and just like a strain gauge, have limits on how temperatures impact them.
Power is normally calculated through torque readings because is the variable.
Power =force x distance/time
Distance is set by the design of the "machine" being measured, and time is time.
But in the case of a strain gauge type meter, it's all essentially estimations based on algorithms and snapshots of the torque on the pedals.
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Jthanmyfitnesspal wrote: »@NorthCascades : impressive! I didn't know they reported instantaneous torque. That's useful.
To work, they they need to determine the mean torque and multiply by the angular velocity (to get power). Ideally, on both sides (I wonder how much that matters). For the versions built into the pedals, the force has to be converted to torque, which is not that easy (or accurate), since only the component perpendicular to the crank counts. Actually, it's amazing the pedal implementations are at all accurate (are they?).
And, do I need to say it again? the conversion to calories burned varies quite a lot between riders.
The "torque effectiveness" data measures exactly what you're talking about in the second thing I've bolded. You aren't the first person to think of this stuff. 🙂 Yes, it can be measured correctly.
This is also what those power phase diagrams are showing you:
The left and right PP are the parts of the circle through which you're currently producing torque that goes to the road. Pioneer exposes even more data about this.
I mean I could tell you that launching a spacecraft out of the solar system and being able to still get data from it is really hard. I could even tell you the Voyagers aren't doing that, I would be wrong.
If you decide you want to measure power at the pedals instead of another place, then you have a choice. You can buy a set of pedals that measures the left side only and doubles the reading, or you can buy a set that measures at both pedals. I use bilateral ones. Turns out of you tell the shop what you'd like to pay, they can be very accommodating when you just bought a complement bike too.
To your question whether unilateral vs bilateral matters, nobody has a perfect 50/50 split at all times. It gets closer to 50/50 during more intense efforts. Training isn't an especially demanding use of power data and people manage to train effectively with them. They're not good enough for aerodynamic testing.
You can measure power at the rear hub and many other places in a bike instead of the pedals if you choose to. I use pedals because they're quick and easy to move between bikes.
To the third bold, what you're saying is flat out false. You seem to be misunderstanding the study of 14 people you linked to with its 6 different ways of looking at effeciency, which (your link) says the range of efficiency at turning chemical energy into work varies incredibly little between individuals.0 -
NorthCascades wrote: »robertw486 wrote: »From the peer reviewed stuff I've seen personally, I'd say the manufacturers claimed accuracy rarely holds water,
I wonder why false advertising lawsuits haven't put these fraudsters out of business?robertw486 wrote: »NorthCascades wrote: »robertw486 wrote: »From the peer reviewed stuff I've seen personally, I'd say the manufacturers claimed accuracy rarely holds water,
I wonder why false advertising lawsuits haven't put these fraudsters out of business?
I can't say.
I can. Because the massive fraud you're suggesting isn't happening. 🙂
SRMs used to cost $3,000. The first set of Vectors I had cost $2k. They have seen advertising accuracy spec which isn't hard to verify. Occasionally one is operating out of spec and the company replaces it.
I'll help you understand about repeatability in a following reply.0 -
Jthanmyfitnesspal wrote: »NorthCascades wrote: »A power meter these days has a maximum error of up to 2% but most are less than that. You can literally look up the maximum error specification for a power meter before you decide whether it's a good value or not.
The accuracy of the power output is very good. And, I would argue that the repeatability may be more important a metric than the absolute accuracy in terms of it's helpfulness as a training tool.robertw486 wrote: »I'd say the manufacturers claimed accuracy rarely holds water, and it's more of a measure of repeatability as mentioned by @Jthanmyfitnesspal above.
First of all it's a huge jump from "you can get fitter without perfect data" to "these produce bad data." That's just not logically supported, speaking of things that hold water. 🙃
Here's a thing that happened.
Everyone used to ride skinny 23 mm tires with rim brakes. Now everyone who bought a bike in the last 5 years is on disc brakes, and they can't use their PowerTap wheel on the new bike. So they had to buy a new power meter for it.
Guess what happened?
Repeatable measurements of power. Your FTP on a p2m isn't meaningfully different from your FTP on Rotor Rings or Vectors or C2s.
How do people get repeatability across multiple units without accuracy? Do all these competing companies all agree to systematically bias their readings exactly the same way for the benefit of someone else's customers? Would you like to buy a bridge? 😉1 -
Jthanmyfitnesspal wrote: »To work, they they need to determine the mean torque and multiply by the angular velocity (to get power). Ideally, on both sides (I wonder how much that matters). For the versions built into the pedals, the force has to be converted to torque, which is not that easy (or accurate), since only the component perpendicular to the crank counts.
Garmin named them Vectors because of their measurement of torque vector. (Which, obviously, is combined with angular velocity and lever length to arrive at power.)
How did you think this works? Did you really think people have been spending thousands of dollars on a pair of dice for 30 years?1 -
Any why is it so important to believe that everyone else is wrong and you've uncovered a secret that tens of thousands of scientists have missed, hiding right there in plain sight?2
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What are we "debating" again?
I'm just wondering if there's a meaningful difference between "pedal mashing" and "spinning"... Am I in the right place?2 -
What are we "debating" again?
I'm just wondering if there's a meaningful difference between "pedal mashing" and "spinning"... Am I in the right place?
If that's what you're seeking, maybe not. If you're seeking cycling enthusiasts geeking out about power meters and their accuracy, in a quite technical but informative way, with some fun hyperbole and quips along the way . . . c'mon over here, I'll share my popcorn. 😉1 -
What are we "debating" again?
I'm just wondering if there's a meaningful difference between "pedal mashing" and "spinning"... Am I in the right place?
If that's what you're seeking, maybe not. If you're seeking cycling enthusiasts geeking out about power meters and their accuracy, in a quite technical but informative way, with some fun hyperbole and quips along the way . . . c'mon over here, I'll share my popcorn. 😉
I do like popcorn...2 -
What are we "debating" again?
I'm just wondering if there's a meaningful difference between "pedal mashing" and "spinning"... Am I in the right place?
If that's what you're seeking, maybe not. If you're seeking cycling enthusiasts geeking out about power meters and their accuracy, in a quite technical but informative way, with some fun hyperbole and quips along the way . . . c'mon over here, I'll share my popcorn. 😉
I do like popcorn...
I'll bring the pickles!!!2 -
DCRainmaker compared about 10 different PMs.
Either the different manufacturers are deliberately skewing the numbers by the same amount (which would still require damn good accuracy) or they are all pretty damn accurate.
For the single-sided v double-sided issue personally I went for single-sided purely on cost but I also knew my typical power split is 49/51 or 50/50%.
BTW OP - Did you get a response from the authors of the study when you told them the conclusion they came to after designing, executing, analysing and reviewing the study was wrong?
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What are we "debating" again?
I'm just wondering if there's a meaningful difference between "pedal mashing" and "spinning"... Am I in the right place?
@jjpptt2
I touched on that earlier in this entertaining train-wreck.
The answer is no, even elite level riders (especially sprinters) are being told just to concentrate on pushing the pedals as hard as possible. I was fortunate that my cycling mentor is connected to one of the top mechanical sports research physios and yes it has been tested in that search for every last 0.01% of performance that matters to the truly elite (national and olympic level).
The explanation I got from my cycle coach/cycle fitter was that concentrating on spinning compromises your push more than it helps, what little you gain from your hamstrings is lost from your quads basically.
Just enough to unweight the rising pedal is perfect but we are talking minor differences between the guy who rides a fixie up and down Alpe d'Huez to perfect his spinning and a complete pedal masher.4 -
NorthCascades wrote: »NorthCascades wrote: »robertw486 wrote: »From the peer reviewed stuff I've seen personally, I'd say the manufacturers claimed accuracy rarely holds water,
I wonder why false advertising lawsuits haven't put these fraudsters out of business?robertw486 wrote: »NorthCascades wrote: »robertw486 wrote: »From the peer reviewed stuff I've seen personally, I'd say the manufacturers claimed accuracy rarely holds water,
I wonder why false advertising lawsuits haven't put these fraudsters out of business?
I can't say.
I can. Because the massive fraud you're suggesting isn't happening. 🙂
SRMs used to cost $3,000. The first set of Vectors I had cost $2k. They have seen advertising accuracy spec which isn't hard to verify. Occasionally one is operating out of spec and the company replaces it.
I'll help you understand about repeatability in a following reply.
I don't need any help at all understanding repeatability, as an average. What I fail to understand is why you would accept manufacturers claims of accuracy and error when studies show otherwise.
Here is independent verification.... where is the maximum of 2%?
Actual study results
Here's another study, showing variation and temperature influence....
Actual study data
From the above....
Results:
The mean error scores for SRM and PT factory calibration over a range of 50–1000 W were 2.3 ± 4.9% and −2.5 ± 0.5%, respectively. A second set of trials provided stable results for 15 calibrated SRM after 11 months (−0.8 ± 1.7%), and follow-up testing of all PT units confirmed these findings (−2.7 ± 0.1%). Accuracy for SRM and PT was not largely influenced by time and cadence; however, power output readings were noticeably influenced by temperature (5.2% for SRM and 8.4% for PT). During field trials, SRM average and max power were 4.8% and 7.3% lower, respectively, compared with PT.
The last I checked, errors of 5.2%, 8.4%, 4.8%, and 7.3% are all greater than 2%.
Once again, the majority of meters are simply approximating power, then smoothing it. Most these days don't even have a true crank rotation reading, they rely on accelerometers and approximate that as well. True power measures have exacts, sync'd with exacts of time, and often rely on a LOT of samples per rotation. This applies to bikes or huge car chassis dyno's. A guess is a guess, a known is a known.
But then again, so far you have ignored all the data from linked studies, and simply claimed to know the answer. What studies or independent data support your claims?
You are questioning people that have provided the basis for their claims. It should be easy to provide a basis for your own claims that supports your conclusions.
Human GE varies, supported by studies. Power meters aren't within 2% accuracy, supported by studies. You can insert any claim that disputes those studies, but if the only basis is "because someone said", it's not very convincing.
And for the record, I don't think anyone has claimed that either GE or PM data were grossly incorrect at all times. I'm just giving examples that error added to error, then stated as an average, can be misleading.1 -
What are we "debating" again?
I'm just wondering if there's a meaningful difference between "pedal mashing" and "spinning"... Am I in the right place?
No, this is more about the differences in averages and absolutes.
If each piece of popcorn, on average contains adequate butter, that won't help when you get all the pieces without butter. If I take the popcorn from the bottom, the extra butter will average it out though, so it's all good.
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BTW OP - Did you get a response from the authors of the study when you told them the conclusion they came to after designing, executing, analysing and reviewing the study was wrong?
I'm tempted, although it's a pretty old article. Their use of the phrase "no differences in efficiency" would not be allowed in the journals where I publish. You would have to say that the "population means are within stated errors," or something like that. But this is physiology, not physics or engineering, and it is generally a bit less rigorous.1 -
What are we "debating" again?
I'm just wondering if there's a meaningful difference between "pedal mashing" and "spinning"... Am I in the right place?
If that's what you're seeking, maybe not. If you're seeking cycling enthusiasts geeking out about power meters and their accuracy, in a quite technical but informative way, with some fun hyperbole and quips along the way . . . c'mon over here, I'll share my popcorn. 😉
Power meters can tell you about metabolism too. 🙂
The blue line is a ride I did the other day. The gray line behind it is a summary of the last 35,000 miles I rode.
Notice the sharp inflection point at 30 seconds.
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DCRainmaker compared about 10 different PMs.
Either the different manufacturers are deliberately skewing the numbers by the same amount (which would still require damn good accuracy) or they are all pretty damn accurate.
For the single-sided v double-sided issue personally I went for single-sided purely on cost but I also knew my typical power split is 49/51 or 50/50%.
BTW OP - Did you get a response from the authors of the study when you told them the conclusion they came to after designing, executing, analysing and reviewing the study was wrong?
I bought the left and right pedals. I don't disagree with your thinking, and most people's physiology is pretty consistent. Everyone who uses a single pedal meter is able to use it to good effect, and the proof of pudding is how it tastes. 🙂
Once I injured my feet, I was very glad to have have the bilateral measurement. Turns out the L/R balance isn't that useful even when one for us more injured then the other, but the platform center offset can be invaluable when you have an injury related to a tendon you supinate on.0 -
What are we "debating" again?
I'm just wondering if there's a meaningful difference between "pedal mashing" and "spinning"... Am I in the right place?
About 10 years ago, I bought a power meter, and used it to get faster.
After a while, that changed, and I used it to maintain what I've got.
"Time wounds all heels" (RAH) and now I'm having to use it to do all kinds of crazy *kitten* just to not be even slower.
One of my jerseys slows me down by ~15w @ 25 mph when I unzip it a couple inches. You can detect that with a PM and a good speed sensor (GPS doesn't work for this, neither does a L only meter), and a clever way of gathering data. I think it's because the shoulders loosen and start flapping. I got a jersey with a "race neck" and don't have that problem when I swear it, so I got a couple more. 🙂 Think how much training it would take to increase your fitness by 15 watts!
Like most people, I'm actually faster on the hoods with my forearms parallel to the ground and my elbows bent to 90*.
And on that note, a $200 set of tires gets you about the same amount of fast (compared to Gatorskins) as $3k wheels.3 -
I think a powermeter is a great tool for training.
I think I'm past that now, and I would just be monitoring my power as it declines over time. Not as much fun.0 -
For what it's worth, you can find a used power tap hub for as little as $100 if you aren't in a hurry. That's around here in a big city. There's a 50/50 chance it'll come with the wheel it was built into and the front one too. Road cycling has moved from 23 mm tires, tubular preferred, and rim brakes, to 25-28 mm rubber, tubeless capable preferred, and disc brakes; you can't give tubular wheels away. Those old hubs don't work in newer bikes.
As a record of decline, it's sad. I thought this getting old stuff was something that happened to other people, and exercising enough would at least hold it off. I find it really useful for helping me figure out how to require less power and still be fastish. I don't expect to be fast all the time, but I want to stay competitive in beer league racing. And seggies. I wouldn't do a crit today, but that's probably as much about learning that I'm not immortal and don't like getting injured.2 -
I understand a few simple things about riding. With a power meter, heart rate monitor and software like Xert there’s no hiding😂 I know when I’m putting down some good power or when I’m off and need to recover. What I can’t understand is how a 4 hour hammerfest burns less calories that someone constantly walking around obsessing about their Fitbit. You don’t think companies would do that on purpose do you?1
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What I can’t understand is how a 4 hour hammerfest burns less calories that someone constantly walking around obsessing about their Fitbit.
Yeah, I can't understand that, either. Maybe you can clarify. My biggest calorie burns are my 1-2h rides. I never get much from just walking around. (Unless it's up a mountain.)0 -
I understand a few simple things about riding. With a power meter, heart rate monitor and software like Xert there’s no hiding😂 I know when I’m putting down some good power or when I’m off and need to recover. What I can’t understand is how a 4 hour hammerfest burns less calories that someone constantly walking around obsessing about their Fitbit. You don’t think companies would do that on purpose do you?
Fitbit when you select a workout is going into HR-based calorie burn, and for most walking is an inflated calorie burn.
Even if the formula had your measured stats of HRmax and VO2max instead of estimates, the HR-based formula inflates calorie burn at the bottom and top of the aerobic range - the only range where it could even be a good estimate.
For compare it also depends on how slow you are riding to complete 4hrs on the bike. Hammerfest avg power changes for me the amount of time I go.1
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