Hello, In Garmin you can set your heart rate zones using Maximum Heart Rate (MHR) or Heart Rate Reserve (HRR). Default percentages are based on MHR but they look more suitable for HRR. Click on the link, set your MHR and Resting Heart Rate (RHR) and check differences of beats between MHR and HRR modes with Garmin default percentages. Then, if you want, you can use my own percentages for MHR based on pace for endurance fundamental, marathon, half marathon and 10km.
Cheers