This is based on the fact that every time I do a run with my 920XT, a bunch of extra calories get sent to MFP on top of the run activity via the Garmin Calorie Adjustment.
Looking at the detailed calorie breakdowns on Garmin Connect seems to back this up, as a bunch of rogue walking calories seem to be created and these are pretty much proportional to the number of steps for the day, some of which were recorded while running.
I think this links to the issue I reported a few weeks ago, that Garmin are supposedly working on. Some links....
https://forums.garmin.com/showthread.php?189131-Inconsistency-with-Active-Calories-on-the-Reports-section
https://forums.garmin.com/showthread.php?195187-Garmin-VivoSmart-Active-Calories-vs-MyFitnessPal-Exercise-Calories-Discrepancy
https://forums.garmin.com/showthread.php?188882-Mismatch-between-calories-on-Garmin-Connect-and-MFP-adjustment
Any thoughts?
Paul