Hi,
I just recently discovered that if I am signed in to Garmin Connect and view other persons activities, GC actually uses settings from my profile for heart rate percentages and zones.
As an example, looking at Ryder Hesjedal's log from TdF yesterday:
http://connect.garmin.com/activity/39457636
He has an average heart rate of 144, and when I switch to percentage view this is said to be 80% of max, which would mean his max heart rate is 181. That's clearly wrong for him, but it is correct for me.
In other words, Garmin Connect uses MY zones and max values in the calculations. That's just plain stupid.
