Better that just follow 180-age rule, its more accurate if you do this:Find your lactic threshold HR by detecting you average HR while running 20 min at full speed (prior a 10 min high intensity warmup) then subract then 20 beats from that and they you have your max MAFF pace… This ease very similar to Z2 speaking on Joe Friel zo08#&se23n;.For me numbers would be 175 (Lactic Threshold) – 20 + 155 BPM… So my long runs are 145-155 bpm, about a 4:50 min/km pace on flats.This is 7 beats higher than maffetone fomula (180-33 (age)=148