Active Calories recorded by Edge 830 + Power Meter are overwrited by Hrm-Pro

scalax said:

Why calories recored with the Edge 830 + power meter are being overwrited by those calculated with the HRM-Pro?

The problem is that the power meter only measures the power output of your legs (the kinetic output), while the body burns much more during the ride (many muscle groups work during the workout, and the brain burns considerably more than the RHR too). So using the HR for the Calories expenditure is (in theory) more adequate, and makes sense.

That told, I admit that the discrepancy between the value with and without the HRM, as shown in your example, is rather high, and it is a question whether it really comes from the difference of the HR detected by the F6 vs. the HRM belt. It almost looks like there might be a bug, summing values from both of them. To test whether it is the case, you could disable the wrist HRM on the F6, link the HRM belt with the F6, and repeating the workout, to see whether you get a comparably high value, or rather just around the half of it.

Hello Trux, thanks for your reply.

Please not that my Fenix 6 Pro was not used during this test. I just reported that i had it during the night before going out for cycling.

The test was made with Edge 830 + Power Meter and HRM-Pro strap on (this one was not connected to Garmin Connect until the last screenshot were i added the strap back in Connect and let it synch its data).

From my personal experience calories data coming out from Power Meter is way more accurate than the one coming from HR data.

Take this as an example.

I have 260w FTP and weight 64kg. My friend, way stronger and fit than me has 325w FTP and weights 68kg and is 10cm taller than me.

In the same cycling session the calories output derived from HR of my friend was close to mine just because my average hearth rate was 10 beats higher than the one of my friend. This is physically impossibile since my friend was having at least 30w higher average power for the whole session.

When you have a power meter, even if it doesn't take into account the rest of the body, the calories output is way more accurate.

The problem here seems that HR-Pro data, when synched, overwrites those of the activity recorded with Edge 830.

scalax said:

From my personal experience calories data coming out from Power Meter is way more accurate than the one coming from HR data.

As I wrote, the data from the power meter only shows the kinetic energy burned by the legs. It completely ignores the energy expenditure of all the rest of your body, so it cannot show the true active Calories, rather just the kinetic energy.

scalax said:

In the same cycling session the calories output derived from HR of my friend was close to mine just because my average hearth rate was 10 beats higher than the one of my friend. This is physically impossibile since my friend was having at least 30w higher average power for the whole session.

The Calories calculation is much more complex than just directly using the HR. There are many more factors playing the role - the Resting HR, the Lactate Threshold, HR Zones, HR Variability, body mass and height, respiration rate,...

The question is also why the power meter of your friend was showing 30W more. Was he riding in front of you all the time, having more aerodynamic drag? Or using inefficient gear? Worse bike? Still, even if he burned more on the power meter (and assuming both power meters worked accurately, which could be doubtful), it does not necessarily mean his body could not burn less. You could only tell if you made a calorimetric test in a lab.

Let's forget about me and my friends for the moment, we don't have data about this at the moment.

Let's take into account more data to see how the HR estimation is completely wrong.

This is my resume of the last Novecolli i ran two weeks ago. Equipment: Edge 830 + HRM Pro. Burned calories 4629, resting calories 626, total calories 5255.

This is the daily resume for the same day

Can we really think that i burned 9509 calories in a day?

I see your point when you say that the power meter doesn't take into account the rest of the body, you are right. But clearly these data cannot be right.

scalax said:

Can we really think that i burned 9509 calories in a day?

Well, I do not know what you really burned, and how accurate the numbers are, but as I wrote, taking just the Calories from the power meter would not be correct anyway.

However, if you take your activity data and the classical formula for the raw estimate of the energy expenditure at biking (watts * hours * 3.6 [source]), then it gives 166*7.75*3.6 =  4631 Calories, which is almost identical to the 4629 Active Calories shown in your activity stats. Hence, I'd tell your HRM-based Calories calculation works pretty well.

trux said:

However, if you take your activity data and the classical formula for the raw estimate of the energy expenditure at biking (watts * hours * 3.6 [source]), then it gives 166*7.75*3.6 =  4631 Calories, which is almost identical to the 4629 Active Calories shown in your activity stats. Hence, I'd tell your HRM-based Calories calculation works pretty well.

But as you can see from the daily resume active calories are 7588 and not 4631. There are nearly 3000 calories more.

Trux, it is the same example as this morning. The problem is not in the activity. The problem is in the daily resume where the HRM-Pro data overwrites those of the Edge 830 activity.

The daily resume contains all active Calories from the whole day. It means every second where your HR is elevated above the Resting HR will produce active Calories. And due to the excess post exercise oxygen consumption (EPOC), it will be significant after such a long workout. So nothing surprising, from my point of view, in this specific case.

The problem is that there were already 2000 calories in excess after the race. Like this morning there were 600 calories in excess just after i synched.