Having established your Average power and Normalised power, you can now look at your Variability index. So as we have said, the Average power measures all the variants your ride produces throughout, including stopping for traffic lights, (or in race conditions, coasting); and Normalised power takes out the ‘peaks and troughs’ on the Average power graph. So it’s the power you could have maintained, at the same physiological cost.
Now think about the body, what we are looking for is a smooth workout without too many power surges as they cause physiological cost, in terms of glycogen utilization, lactate production, stress hormone levels, and neuromuscular fatigue.
What we need to know is the variability between the two:
Normalised power / Average power = Variability index
The ideal Variability index is 1.0 as it means you’ve achieved a really smooth output of power. If the VI is higher than 1.0 it suggests poor pacing and power application. In reality, ‘we are not machines’, so 1.0 is elusive, there will be a variant, but the lower the variant the better.
Training using the Variability Index
So how might you learn to ride with a low variability index? On your cycling computer, enable 3-second data averaging:
Adjusting cadence for a consistent Variability Index
Adjust your cadence to average within 10 watts of your target power at all times. Pay attention to the amount of pressure you are applying to the pedals at your target power, as this pressure begins to increase or decrease, it is time to either gear shift or adjust your cadence.
Will different terrains affect my course Variability index?
As you can imagine the course you take will have a bearing on the Variability index. On a flat course, you can get closer to 1.0, on hills, you might get 1.04-1.07. If power often spikes or dips when climbing or descending, it might be time to re-evaluate the gearing on your bike.
Racing using the Variability Index?
The Variability Index should be considered for Time trials and Triathlon where smooth pacing is imperative. Road racing, however, produces higher readings as you are surging and attacking.
In summation, using the Variability index will improve pacing. You will learn to adjust your cadence and after a few weeks using your power meter, you might even find you are adjusting to keep your target power, without looking at your head unit.
Normalized Power (NP), Intensity Factor (IF), and Training Stress Score (TSS) are registered trademarks of Peaksware.