Best I can tell, Garmin collects all the necessary data in wearables, bike computers, and collected heart rate data from other devices (Sufferfest, Concept2, etc), but they inconsistently add the data in Garmin connect. This make the measurement pretty useless if you do different things. There are a ton of questions about this issue on this forum, but Garmin doesn't seem to care. They should delete the idea of "intensity minutes" if they can't support the metric consistently. It just irritates customers.
