Normalized Power (NP) and Variability index (VI)

 

  1. What is the Normalized Power and Variability Index?
  2. How to interpret it?

What is Normalized Power and Variability index

 

Normalized Power is weighted average power from your workout.

What is that mean?

It’s mean that higher watts are more weighted, for example:

1-hour perfectly steady workout at power 200W give as Normalized Power = 200W
1-hour workout with 30 min at power 100W and 30 min at 300W give as Normalized Power = 250W

Now you see the difference.

If you go for a short workout with 1 min max intervals you can see a huge difference between Avg. Power and Normalized Power.

This difference we call Variability index (VI) which is normalized power divided by average power.

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Variability index

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How to Interpret it?

 

A single number is just metric but to get conclusions you need to compare to another number.

We did compare Normalized Power (NP) to Average Power from the workout.

The result from it is Variability Index (VI).

Variability Index should be always higher or equal to 1, (you can see it lower than 1!*)

!*Note. If your bike computer is set up to “don’t include 0 in average power” it can mess up Variability Index!

because Average Power will be higher than Normalized Power what give us VI lower than 1. It is wrong data to interpret.

Variability Index can be from 1.00 to around 1.40.

1.00 is a perfectly steady workout, that how we would like to race time trial.
1.00 – 1.05 is a standard time trial.
1.05 – 1.15 is a casual workout.
1.15 – 1.20 is a typical road race.
1.20 – 1.40 is mountain bike race.

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