XM ( HR only) vs. Garmin Edge ( Power): One Ride with two different results !

Today I rode my rollers running Xert Mobile with only heart rate strap & cadence sensor ( no power) on one end AND Garmin Edge with Power meter, cadence and HR on the other end. The Watt numbers (that MX derived from HR ) were trailing below what Garmin glean anywhere between 25 to 40 watts but there were a few second when they matched. Also The MX watt were very jumpy, up & down, so were the cadence number as well, jumpy ! So thought that the cadence fluctuations were effecting the Watt outcome so I disabled the cadence and the watt issue persisted. I have both ride on my Dashboard ( just deferent time b/c Of Xert issue with time).
I was not expecting 100% match but 10% to 15% is to much of a discrepancy .

As mentioned, the calibration of HR Derived Power is still to come. You can try and adjust your Minimum/Maximum HR as these can affect the accuracy.

The first derivative of HR can be quite jumpy and the algorithm depends on this. Hence, you can see variation, more so with inaccurate HR monitors. I find the Polar H7 to be one of the best HRM’s out there and it provides the highest stability in HR derived power.

All-in-all, I wouldn’t be looking at second-by-second numbers but look at the overall XSS, Carb usage and MPA data to some degree as these can match quite nicely when all is setup correctly and when an accurate HRM is used. These values can be very valuable for training and the carb/MPA could eventually be used in real-time during non cycling sports.

Armando, I trained today and I kept adjusting my MHR- on the fly for the first 15 minutes - and managed to get XSS, on both XM and Garmin IQ, ticking up at the same pace :). very very good. the Fat usage was less and the Crab was higher on XM than Garmin, by not too much though. excellent .

Nice. Manual calibration! Glad you managed to get it to a point that works well for you.

One thing I noticed and it make a lot of sense, when I’m out of the saddle for over 2 minutes (sustaining the same power output while I’m seated ) the heart rate - of course- goes up resulting on skewing the Power and therefore ,XSS and other metrics. And let’s not forget the “Cardiac Drift” factor that associated with HR based training in long duration rides. But all in all I’m happy with the results.

But is it possible that the power meter based XSS calculations are the values that are skewed lower by not accounting for the added strain that riding out-of-the-saddle generates? Or when you’re on long rides? Food for thought…

My experience was like this( you tell me what’s involved) I was riding my rollers seated and at the 40min mark the XSS GE power based and XM HR based were trailing beautifully at 41 XSS! ( XEP-GE was 230 and 234 on XEP-XM or something around that) then I decided to do 20min of 2min OOTS and 2min seated, that’s when I noticed XSS-XM starts going a little faster than XSS-GE! I think by the fifth cycle of OOTS drills, the XSS-XM was higher by 5-6 points.
Keep in mind, I maintained my Avg power on GE the same, on both positions of seated and OOTS, I didn’t apply extra strain on OOTS. But hey, lemme run the experiment again. Ty.

Hello Armando, sorry i had to jump back to this discussion from last year! XM is not working lately ( only HR strap) not showing Watt output, i made sure " Auto-Enable Derived Power" is ON and BPM is reading correctly. Alos what are Red and Yellow Zone ( on XM, Setting- Options) mean/ for ? TY.

Which version are you using?

I’m using 2.2.9 (106).

If you enable the “Smoothed HR - bpm” and “Derived Power” fields on the activity tab and start an activity with a heart rate monitor connected, do they show anything, or just “NAN” and “0” ?

Oleksiy, I’ll try tomorrow and I’ll report back! thank you.

Oleksly, I tried tonight and it worked :).TYVM.