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Cycling efficiency for different riders (it varies a lot)
Replies
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Jthanmyfitnesspal wrote: »And I think that is a pretty intuitive fact: if you put an untrained and heavy person on a bicycle on a flat course, there is no way they would have the same efficiency as a much lighter trained person for the very reason that their legs are heavier and take more work to pump (regardless of power applied) and they probably don't unweight the rising pedal very well. All this lowers their efficiency.
That's like saying that it taking 1/3 your body weight in pounds to walk a mile could be off by a lot depending if you walk a lot. No. It will feel more difficult and you won't be able to do as much of it if you're out of shape.
This has been studied so many times.
The range of possible error here is plus or minus two and a half percent. That's a 5% range, not a two and a half percent range. If you did 100 joules of work, you burned anywhere from 97.5 to 102.5 calories, for a total uncertainty range of 5%. Maybe understanding this will make the rest of what's going on easier for you to come to trerms with?1 -
Please don't misrepresent what people are saying to you. You can't just swap terms to create a strawman to bolster your amazement. Debate should be about what people actually say or write and not what you think they say or mean.
Good PM's claim closer to +/- 1% accuracy in measuring power output - the technology has been around for decades before it was ever applied to cycling. Read some comparison tests by DCRainmaker if you are truly interested in the subject.
I don't think anyone who has responded misunderstands what VO2 max means, they also understand that a VO2 max score and total oxygen uptake are not the same thing.
Your mind seems closed on the subject in that you have an unshakable belief and are searching for snippets of data to support your belief even when the study you picked doesn't. If you found anything in there that dismisses the relationship between watts and net calories please do quote it because I'm not seeing it.
I'll leave you with the summary of the study................
"In summary, we examined several measures of cycling efficiency
in cyclists who varied widely in their cycling ability; the subjects
induced recreational riders and world-class professionals. Our
data indicated no differences between groups in GE (measured
at an absolute mechanical power or at a relative intensity), DE
or EC In addition, while there was a small (R2
= 0.06) but significant correlation between EC and peak aerobic power, there were
no significant relationships between either GE or OE and measures of aerobic capacity. Thus, our data suggest that the cycling efficiency of elite cyclists is not different from that of trained or
novice cyclists and therefore is not a predictor of success in elite level cycling."
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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. 🙂
Creating mythology in *this* thread? 🤣
Man, this is the MFP forums. Evvverrrrrything is about calories. Gotta get the best fitness tracker because what they're for is to *measure* calories accurately, gotta do the magic HIIT exercises every day to burn the most calories you possibly can, gotta lift heavy to build muscle because muscle burns more calories every day, of course gotta spend $$$ on a power meter *only* to get a better calorie estimate. Why on earth would a person even exercise except to Lose Weight Faster?
Caaaalooooorrrrrieeees!
/sarcasm /rant
This place is weird, sometimes. To me, this thread seems like the occasional rare case where someone(s) are talking about something other than calories. Or trying to, anyway.
🙄
It does seem odd to me to have a critique of a better-than-average way of estimating exercise calories for one exercise, on the basis that it isn't perfect, when most of the other methods of estimating other exercises' calories are practically a mystical art (and a crapshoot). 🤷♀️ Intellectual curiosity, I guess, as you suggested.3 -
Well, this is why I put it in "Debate: Health and Fitness." What I'm trying to say is to look at the data from the original paper I posted, not the words. The words talk about mean values of various cohorts being pretty close, while the data presented in Figure 1 shows a large variation in GE between the individuals. I'm bothering to engage in the debate because I feel like it's misleading and, in fact, seems to have misled a lot of people.
Here's another study that measures a range in "Gross Efficiency" of 18.4–21.4% among a cohort of 14 "physically active men (n = 12) and women (n = 2)," where "Practically, all of them used cycling as their training mode in some part of the year."
https://sportsmedicine-open.springeropen.com/articles/10.1186/s40798-019-0196-x
Again, I just notice it's a pretty wide range among a group of quite similar individuals. Note that it means their calorie burns for an equivalent workout (in terms of energy produced) will vary by as much as (0.214 - 0.184)/0.184 = 16%.
Does it matter? Not really. Everyone everywhere will note that it is your power per unit body mass that matters. And, if you expend a few more calories, then you just eat a few more. Problem solved!1 -
Jthanmyfitnesspal wrote: »I am really amazed that so many of you believe that the efficiency factor (GE) is constant between individuals "to 2.5%" when measured data for GE is staring you right in the face from my original post. Yes, it's plotted vs. VO2max, but don't let that confuse you. The range of measured GE values presented in that little study is from 14.5% to 22.5% for different individuals.
The power measured by the bicycle power meter is probably pretty good (I'd think it could be measured to within 2.5%, for example), but the conversion to calories burned by the rider is much less certain, particularly among casual riders.
And I think that is a pretty intuitive fact: if you put an untrained and heavy person on a bicycle on a flat course, there is no way they would have the same efficiency as a much lighter trained person for the very reason that their legs are heavier and take more work to pump (regardless of power applied) and they probably don't unweight the rising pedal very well. All this lowers their efficiency.
Here's the thing though - it took so much energy to produce that power. Call it 165 watts for 1 hr.
165W x 1 hrs x 3.6 = 594 cal is the formula it seems many of us are saying assumes the 20-24% conversion of chemical to mechanical energy.
You need to take weight out of the equation first - so make your 2 riders same weight & size on same bike and route - 1 casual not skilled tad in shape, 1 pro with their skills. Same speed will be reached with same power.
Casual has VO2max 30 ml/kg/min, pro is 60.
Casual has HR that is at their lactate threshold the whole time - they are dying in order to get enough blood flow for the required oxygen to power their fat-burn-inefficient-carb-burning muscles.
Pro has HR that is in middle of aerobic zone - barely breathing to supply enough oxygen for their efficient-fat-burning muscle.
It would seem one would be burning way more calories than the other.
Now both of them are walking fast.
1 mile same route. Same pace doesn't even matter that much - but say yes to same pace.
Casual has higher HR, breathing hard.
Pro has lower HR, barely breathing above resting level.
Are they burning the same calories?
Are they putting out the same power to move their same mass the same pace?
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"Everyone everywhere will note that it is your power per unit body mass that matters. "
Matters for what?
Yes it matters as a performance metric. Watts per kg is always an interesting comparison.
I'm reminded of it every time I ride with someone who produces four fifths of my power but weighs two thirds of my weight.
Doesn't matter for people on MFP wanting a net calorie estimate for their cycling.3 -
Jthanmyfitnesspal wrote: »Everyone everywhere will note that it is your power per unit body mass that matters.
For your speed going up a hill steeper than about 8%, power to weight (w:kg) is what decides who goes the fastest. The rest of the time it's power to coefficient of aerodynamic drag. But that's only about going fast. Anyway, I've never known anybody to actually display w:kg on their Garmin. 🙂 (I have mine set to show me a rolling 3 second average of raw watts.)
At the end of the day taking the kJ you did and turning it into kC gets you within +/- 2.5% of god's honest truth. That's just what it is.1 -
In terms of weight. I lose it a little faster than the math would predict when I eat to MFP calories and ride a lot. I wondered why for the longest time and then it finally hit me. Every other kind of exercise in my Garmin includes BMR calories in what it reports for c burned when you look at an activity. Apparently all fitness trackers do that and MFP expects it. For cycling, Garmin takes the number of kilo or mega joules I did and turns it into calories. So my BMR is missing in the MFP math. I ride about 8 hours a week, that's a decent chunk of BMR to not include in the math.2
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Runners are lucky. It takes more fitness to run faster, and on flat ground the relationship is close enough to linear. You can use it for pacing so you don't blow up, runners have a 5k pace and a marathon pace.
That doesn't work on a bike. Our speed range is too big. You'll see people doing 7 or 8 mph on bike paths, and you'll see people on race bikes doing 30+ mph. Air resistance rises with the square of speed, the energy required to overcome it rises with the cube of speed. When you get in another cyclist's slipstream it cuts your energy requirement in half. So just knowing your speed doesn't mean much. Speed record on a bike is close to 200 mph, she was drafting a van.
A runner can use their 10k pace as a speed limit so they don't burn all their matches at the start and then limp to the finish line. We don't have that, so we invented power meters as an objective way to measure effort. So a flat 40k, time trial distance, I'm slow (lacking in endurance) and 75 minutes is fast for me. Garmin tells me my best 60 minute power, and other durations too. So instead of going all out and then fading, dramatically at the end, you ride to your maximum sustainable power for that duration. Like your marathon time.
That's why power meters were invented 30+ years ago. Specific training targets, and pacing. In the beginning, using one in a race was almost like cheating, the info is so useful. 🙂 Racing isn't about going fastest, it's about crossing the finish line first.1 -
Here's some insight:
There are ONLY two ways to get faster on a bike.
1. Make more power.
2. Need less power.
That's it, not that you can't do both together. First route is to get fitter, such that you have more energy to deliver to the pedals. Second route is to lose weight for hills, ride a more aero posture, buy supple tires and slippery clothes, choose your line wisely, and avoid the brakes.
That's why people buy expensive power meters, because it plays a central role in speed, and is incredibly useful for training and racing. (In a race, a power meter helps you use as little energy as you can so that you're fresher and have more to give when it's most important.) The calories thing is very cool, but it's more of a curiosity.1 -
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
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