Does Garmin use Firstbeat calorie calc method when biking w/ a powermeter paired?

- over 6 years ago

Hi all,

I am curious whether Fenix 5X has the same bug (feature?) as Fenix 3 HR has.

The calorie calculation of Fenix watches, both of the members of F3 and F5 families, uses the Firstbeat method as a general rule. But when you have a powermeter paired, F3HR calculates the calories burnt as being equal to the work done in kJ.

See some of my posts about it:

https://forums.garmin.com/forum/on-the-trail/wrist-worn/fenix-3-hr/128037-fenix3-hr-calories-way-too-high?p=1060565#post1060565

https://forums.garmin.com/forum/on-the-trail/wrist-worn/fenix-3-hr/128037-fenix3-hr-calories-way-too-high?p=1060625#post1060625

https://forums.garmin.com/forum/on-the-trail/wrist-worn/fenix-3-hr/128037-fenix3-hr-calories-way-too-high?p=1060622#post1060622

Just as a simple example why the 2nd gen Firstbeat method is better. Imagine you are climbing a hill with pretty high HR. Then you are at the top, some seconds later you still have high HR, but you are coasting down with a cadence of zero, so with a power of zero. Your calorie number does not change at all for minutes and minutes, even if your heart rate is being still at an elevated level.

I reported it to both Garmin support and F3 (HR) beta team, but no reaction at all. Some month later, which was 3 weeks ago I reported it to a user HermanB, who is a Firstbeat associate and present here for a while.

First he seemed to be a bit shocked and his first reaction was that I must have been wrong, he assumed that Firstbeat method had to be used always by newer Garmin watches including F3 family. He asked some time to discuss it first with his colleagues and later presumably with Garmin, but since this issue could have been checked within 3 weeks, I gave up. I dont believe I will get any clear confirmation and I dont think I will receive any help from Firstbeat guys to make Garmin fix it for F3 families.

So to cut a long story short: is there anybody het who has both a F5/5S/5X and a powermeter paired, and realized how his watch calculates calories when biking?

If not, can you please simply make a short test?

1. Bike or indoor bike app has to be started.

2. Powermeter has to be connected

3. Then please pedal backwards in order to generate zero power, but make your HR increase.

If your calories is not increasing then F5 family works the same way as F3 family.

Thanks for your help.

Zoltan

0 AllanOlesen67 over 6 years ago

I must say that I have doubted the underlying premise of this thread right since the beginning.

Are there any sources that confirm Tisztul's assumption about heart rate derived calories being more precise than power meter derived calories.

Without knowing much about the issue, I would assume that power meter derived calories were more accurate.

The calories from the power meter depend on an assumption about the relationship between kilojoules consumed and kilojoule performed - the energy efficiency of the body.

The calories from the heart rate depend on an assumption about the relationship between heart beats and kilojoules consumed.

I would expect the latter to have more variability between different individuals than the former.

0 - over 6 years ago

A couple of years ago I spent at least 3 months to collect and read researches about metabolic efficiency of cycling, running and walking. Please believe me the ME is wildly varying between people due to many factors. Pro athlete vs trained subject vs untrained subject. Or ME is totally different at different power level, Or due to different cadence. imagine if a ME is between 18% and 27, then it is a 50% (or 33%) difference, which directly goes into the same error in energy expenditure (EE) calculation.

From the earlier collected researches now I cant point to any, they are on my PC at home, but I already linked one public doc, here it is again http://storage-cdn.trainingpeaks.com...h-handouts.pdf Enjoy the pages about how ME differs at the different level of the factors.

Or check this one https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3761728/

I can't say without any doubt that Firstbeat EE method is better than the questionable power-based EE, since I could read only Firstbeat's document about the validation of their model. But if Firstbeat made no error in their validation, then you have to except the error they published regarding their HRV based EE model. Which is definitely lower than the volatility of ME among people.

An more doubts?

0 - over 6 years ago

Even the ME of one individual can vary at least 10% over years, see https://www.physiology.org/doi/10.1152/japplphysiol.00216.2005

And it is not important why. My only point is that it is just a comfortable statement that the average metabolic efficiency is just the same as the ratio kJ/kcal or in reverse thinking the reciprocal of the ratio kcal/kJ

0 - over 6 years ago

I am at home again and got back to fight for knowledge.

From "Cycling efficiency in humans is related to low UCP3 contentvand to type I fibres but not to mitochondrial efficiency" See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1805795/

"In its essence, efficiency is a ratio between (external) power output and the ensuing energy expenditure (EE). Efficiency may, however, be expressed in a variety of ways. In this study three constructs of efficiency were employed, gross efficiency (GE), work efficiency (WE) and delta efficiency (DE). GE is defined as work rate divided by energy expenditure."

The WE at 40 watt, 80 watt and 120 watt are 25.1 ± 0.5 28.1 ± 0.5 27.6 ± 0.6 for trained subject and 25.9 ± 0.4 27.7 ± 0.8 26.9 ± 0.6 for untrained.

Looking to figure 3 the lowest WE is like 24%, the highest is like 34%

0 - over 6 years ago

From "Cycling efficiency is related to the percentage of Type I muscle fibers" See https://www.ncbi.nlm.nih.gov/pubmed/1501563

From a chart on page 4 and from table 2 the lowest cycling gross efficiency is 18.3% and the highest is 22.6%, delta efficiency is in the range of 18.3% and 25,6%.

0 - over 6 years ago

From "Load and Velocity of Contraction Influence Gross and Delta Mechanical Efficiency" See https://www.ncbi.nlm.nih.gov/pubmed/1521959

"delta efficiency,calculated as the reciprocal of the slope of the linear relationship of the work rate to the rate of caloric expenditure, increased progressively as cadence increased from 60 to 80 and from 80 to 100 RPM (i. e., 20.6:t 0.4%, 21.8:!:0.6%, and 23.8:!:0.4%, respectively; all values significantly different, p < 0.01). DE values, calculated as the mean of the individual delta efficiencies from one work rate to the next, were 20.9::J:0.2%, 21.9::J:0.6%, and 24.5::J:0.5% when cycling at 60,80, and 100 RPM, respectively.DE at 60 and 80 RPM was significantly different from that at 100RPM (p < 0.01)."

"When cycling at 60 and 80 RPM, GE remained stable at values ranging between 20.4-21.0% despite increases in work rate. However, when cycling at 100 RPM, GE increased progressively as work rate increased"

The chart shows me that the GE numbers measured are between like 18.8% and 21%. At 100RPM itself it ranges from 18.8% to 20.6% or so, correlating with the power exerted.

0 - over 6 years ago

FRom "The between and within day variation in gross efficiency" See https://www.ncbi.nlm.nih.gov/pubmed/20464413

The charts are hardly visible for getting exact data, but it is clear that the lowest GE measured is less than 16%, the highest is higher than 23%.

0 - over 6 years ago

After posting so much about the varying metabolic efficiency, whose stable beingness is the basic concept behind Garmin concept of calculating calories from the work you have done, let me quote from "An Energy Expenditure Estimation Method Based on Heart Rate Measurement" of Firstbeat. See at https://www.firstbeat.com/wp-content...estimation.pdf

"Summary of the validation studies
By including information on respiration rate and on/off-kinetics with HR data, the accuracy of EE-estimation improved significantly. Later, when compared with other conventional types of HR-based EE-estimation methods, EEHR+RespR+ON/OFF was shown to be the most accurate method to estimate EE. The accuracy of EEHR+RespR+ON/OFF was even better than methods with laboratory calibration. Other studies have also produced similar results and have indicated as low as 7 % error for the beat-by-beat method developed by Firstbeat Technologies (Wünsch et al. 2005)-"

The mean absolute percentage error of the present Firstbeat method called EEHR+RespR+ON/OFF is said to be 10.9%

So Firstbeat method has an error of like 7% or 10.9%, while people's cycling metabolic efficiency therefore the accuracy of Garmin's "powermeter calorie" approach can vary in the range of 20-50% or so.

Certainly you can say why the whole issue is important at all, which may happen this time, too. To be honest here at Garmin forums I got used to the storyline of first getting some counter-opinions, sometimes they are even real arguments with solid logics, and when I keep on arguing citing more and more data from experts, finally I often get some response about the non-importance of the issue I opened. I just call it the democracy of the ignorant.

0 AllanOlesen67 over 6 years ago

Well, it seems that you have gathered a lot of information on the subject.

I think that your original post would have made a much stronger case if you had included some of that information, instead of just calling Garmin's behaviour a bug without explaining why it should be considered a bug.

0 - over 6 years ago

Yes, you must be right.

But just to be precise, I use the word 'bug' in this thread only once. In my first post it was my first sentence after saying hello: "I am curious whether Fenix 5X has the same bug (feature?) as Fenix 3 HR has".

Thus I also called Garmin's behaviour a feature, too.