I understand that Efficiency Factor is a ratio of internal (HR) load to external (power, speed) load, but what is the range of ratio that I should be aiming for? 1:1 or something else?
Thanks for the question Mark.
To be clear for everyone (including myself):
Efficiency Factor is a ratio of the external (power, speed) to internal (HR) response for the session. We need to correct the way that is written currently.
Cycling: EF = normalised POWER / avg HR. Unit is watt/bpm, but we don't currently show units.
Running:EF = NGP speed / avg HR. Unit is yard/minute/bpm. Also don't show units.
Example calculation for running (see chart): moving NGP 4:31 min/km -> 3.69 m/s -> 241 yard/minute. Moving HR 124. => EF ~ 1.94.
So back to your question: To me, we should recognize that EF will be specific to you. Higher is generally best. So your cycling EF for your example was 1.63. I pulled a random similar 2 hour aerobic bike session from Athletica ambassador pro triathlete Andi Boucherer and it reads 2.01.
So learn and become familiar with your own EF, and keep tabs on it. Rises in the EF suggest enhanced fitness, while reductions might indicate detraining or overtraining. Just one of a number of factors to keep tabs of.
So how should I interpret my results?
If EF for the same workout is increasing over time, does it mean, that I'm making some progress? Can I compare different sessions also, like a steady run and a hard hill interval?