Heart rate has nothing to do with fat loss and the calculation that's been used by all the personal training certifications is just "made up" bullshit.
I am confused as the linked study does not even discuss fat loss, let alone prove that heart rate has nothing to do with fat loss. The study only demonstrates that the HRmax= 220-age prediction formula is incorrect. At the end of the study they suggest a better (but not perfect) prediction formula... HRmax=206-(0.685)*age.