We’ve reworked the way we calculate Active Minutes for Garmin devices in our latest StepSmash release StepSmash Release 1.7.0!
To take advantage of the new method you’ll need to be running StepSmash 1.7.0 or later and you’ll need to set your current age and birth month in your user profile settings. From there StepSmash will compute your heart rate zones and assign active minutes based on them. We put together a detailed guide on how this works How Active Minutes Work in StepSmash.
Going forward I would expect that you see Active Minutes accrue in StepSmash after biking, or any other cardio activity where the tracker isn’t registering much movement even though your heart rate is elevated.