In the help popup for Efficiency Factor it says “Efficiency Factor is normalized watts (output) divided by average heart rate (input).”, however I think the watts are the “input” and the heart rate is the “output”.
It works two ways to measure it, when testing:
- more power for the same average power (the metric uses normalised power).
- lower heart rate for the same power
This can be tested weekly, to see aerobic “fitness” progress. Best is to keep your ride steady, where your HR stays within a range of 2 bpm from LT1/AeT. As you’re get better, you ride for longer up to your intended race distance (if this is a goal). Hence using Average Power (incl. zeros) / Average HR rather than Normalised. The Variablity Index (VI) will then by very close to 1.00.
This is how Joe Friel has intended it to be used.
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Agreed … however, the referenced article on cyklopedia.cc describes it the other way round: “Efficiency Factor (EF) is Normalized Power (NP) (Input) from your workout divided by Average Heart Rate (Output) from your workout.”
So it is at least somehow confusing.
And out of curiosity … why is it better to keep the HR constant? Isn’t the used power something I put into the “system” and the HR is the reaction and hence the output?
The EF metric is Normalised Power / Average HR.
The aerobic fitness test that Joe Friel refers to, is a structured test, i.e. on the same course, same effort and hopefully the same conditions. Like a threshold test (aka the FTP test) is then compared to a base test against which to compare progress, so too is this aerobic test.
If done, uninterrupted, at a steady pace, you can use Average Power as it will close to Normalised.
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Like all connected systems, it depends what you call the sending/receiving system.
In sports science it is common to name the cardiovascular system as the driving system. When you put in an effort, you have to pump more blood to the muscles, thus the HR goes up (input) to respond to the demand of oxygen delivered to the muscles. Those muscles then deliver a higher power (output).
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