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1. What is the Efficiency Factor (EF)?


Efficiency Factor (EF) is Normalized Power (NP) (Input) from your workout divided by Average Heart Rate (Output) from your workout.

Example: 220W / 150HR =1.47 EF

The question that the Efficiency Factor is answering is how aerobically fit, are you?

  • If Output is lower at the same Input then you are more fit
  • If Input is greater at the same Output then you are more fit

2. How to Interpret it?


The question is how to use the Efficiency Factor (EF)?

The Efficiency Factor should be used for tracking your aerobic level. Let’s say you are during your base period and you are doing endurance workout in Zone 2 every week. Example of results:

12/22 – 180W / 130HR = 1.38 EF
12/29 – 182W / 130HR = 1.4 EF
1/5 – 185 / 128HR = 1.44 EF
1/12 – 190 / 129HR = 1.47 EF
1/19 – 188 / 130HR = 1.45 EF
1/26 – 195 / 129 HR = 1.51 EF
2/2 – 200W / 132HR = 1.51 EF
2/9 – 205W / 130HR = 1.57 EF
2/16 – 203W / 129HR = 1.57 EF
2/23 – 206W /132HR = 1.56 EF

We can see a 13% increase. 3 last weeks are very stable, that means your aerobic level get to the point where you need to move on. You can extend your endurance workouts in duration or move to more intense workouts.

Coach Damian

Damian is a head coach and founder of Cyklopedia, which was created with one goal to help everyone be faster cyclists by structured training plans, healthy recipes, and nutrition plans. Damian is racing and coaching for over 10 years, working with athletes all around the world.


  • Avatar spinetrak says:

    “Efficiency Factor (EF) is Normalized Power (NP) (Input) from your workout divided by Average Heart Rate (Output) from your workout.” – that’s a typo isn’t it? I.e.. Power is output and HR is input, no?

  • Avatar James says:

    What sort of EF should you move on at?…… or are you looking at the trend levelling off before moving on?


    • Coach Damian Coach Damian says:

      Hello James, there is no specific number as this number will be different for every individual, but whenever it stops growing at the same effort (workout) you can move on. For example, if your longest workout will be 3h endurance with 60 min tempo and your EF will stop growing, it does mean that you should “move on”

  • Avatar BuckeyH says:

    VI, variability index, is actually normalized power / average power and is a measure of workout or race consistency. This is especially useful in time trials or triathlons where even pacing is very important. The first formula shown here (Example: 220W / 150HR =1.47 VI) calculates EF not VI.

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