Happy that you found the Karvonen method first of all. The intensity is just the percentage of the zones. So zone 2 the lower end would be 0.6 and the upper int

Happy that you found the Karvonen method first of all. The intensity is just the percentage of the zones. So zone 2 the lower end would be 0.6 and the upper intensity of the zone would be 0.7. I'm using (0.5, 0.6), => Zone 1 (0.6, 0.7), => Zone 2 (0.7, 0.8), => Zone 3 (0.8, 0.9), => Zone 4 (0.9, 1.5) => Zone 5 If you are able to reach 215 the problem might be that most of the calculations do 220 - age or something similar for max heart rate.