The Karvonen method factors in resting heart rate (HRrest) to calculate target heart rate (THR), using a range of 50–85%:
THR = ((HRmax − HRrest) × %Intensity) + HRrest
Example for someone with a HRmax of 180 and a HRrest of 70:
50% intensity: ((180 − 70) × 0.50) + 70 = 125 bpm
85% intensity: ((180 − 70) × 0.85) + 70 = 163 bpm