Heart Rate Time in Zone Accuracy

Someone in a comment highlighted differences between the Time in Zone reported by ConnectStats and the one reported in Garmin Connect. So I did some investigation of the accuracy of the time in zone reported by Garmin and ConnectStats. I checked some of my recent activities and also found some discrepancies. Here is a bit of a dive and how to look at it, but my initial conclusion is that ConnectStats seems more accurate.

I look here at a run in the mountains of Switzerland. First you can see the time in zone reported by ConnectStats. You can see first the graphs, but if you tap on the laps cell and select the Heart Rate Zone choice, you can then see details of the numbers computed for each zone.

Screenshot_30_12_2015__21_54 iPhone_6_-_iPhone_6___iOS_9_2__13C75_

Note also that if you hit a given zone, here Zone 5, you can see on the map and on the graph where you were in that zone.


Here it shows 26 minutes in the zone 176 to 190. As a comparison, Garmin Connect shows 47 minutes in that zone and 1:36 in the Z5 zone (above 190), which is interesting because the max HR reported for that run is 189… The settings for the zone in garmin connect is also consistent with the one ConnectStats is using as you can see below.


Garmin_Connect Garmin Connect Time in Zone

As a comparison, Strava shows numbers more in line with ConnectStats, but I was unable to align the zone exactly. For me choosing a custom zone in strava to match the one above 176 to 190 didn’t work and wasn’t picked up by the graph.


Strava time in zone

As a last resort I exported the data for this run to a csv file. You can do that by using the sharing pane in the details activity of ConnectStats, select csv file and email it to yourself. In this case the number also was matched closer to connectstats at 1739 seconds or 28 minutes and change (though not exact, I’ll try to understand why)


So all in all, I’d be interested in other example of mismatch, but here I feel ConnectStats seems more accurate than Garmin Connect, especially for example the fact that Garmin Connect report over 1min30 in a zone that is above the Max HR reported…

If you find a case where Garmin Connect seems more accurate, please send me a bug report that includes the activity and the numbers Garmin Connect reports.