Originally Posted by
RChung
For the purposes of looking at the power/HR "efficiency" ratio, you probably don't want to look at something like NP or xP (though Coggan talked about doing just that back when he first introduced NP -- back before it was even called NP).
It seems that Training Peaks followed Coggan's advice, as this is how they define
Efficiency Factor:
Efficiency factor (EF) is the ratio of Normalized Power to heart rate (cycling) or Normalized Graded Pace to heart rate (running) for a given activity.