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Variability Index Calculator – FTP Cycling Calculator

variability index calculator

The variability index calculator score is a hidden gem that few people know about. Most athletes only care about their FTP, but the variability index is equally important for athletes. A low variability index means minimum stress on your legs and joints, which means lower chances of injury.

A lower variability index also means you are using your energy with more efficiency. Calculating VI is very easy; you divide Normalized Power by Average Power:


What is Variability Index Calculator?

Variability Index Calculator is a simple tool that helps the athletes to calcuate their minimum variability index.

What is Average Power?

Average Power is the mean of the Power you use during cycling in a certain period of time. You usually use a digital power meter to measure, as it keeps track of your speed and Power during your cycling session.

What is Normalized Power?

Normalized Power is the measure of total stress over your body during your cycling session. Normalize Power and Average Power might feel similar, but they are actually very different. Although AP also provides information about how much Power you have put in during your workout, it is not detailed enough.

For example, while cycling through a path with a hill with an incline and decline, where you have to climb up and down. During climbing up the hill, you have to put in much more effort than you are on a flat surface, and while climbing down the hill, you have to put in zero effort.

AP doesn’t register this, and its final value is the same as when you are cycling on a flat route because the double effort you put in while climbing up, and zero effort while coming down cancel each other.

But it is a fact that cycling up and down a hill is significantly more stressful for your legs than a regular flat path, so to take this extra stress into account, we use Normalized Power. It gives detailed information about the stress you have been through and pays special attention to the ups and downs in your output.

How to keep your Variability Index as low as possible?

The ideal variability index is 1, where your Normalized Power is equal to your Average Power. But that kind of accuracy is difficult, so you need to aim for a VI between 1 and 1.05.

To achieve this, you must keep your power output within your zone and as steady as possible. Following are a few things that could increase your VI, and you need to be careful about them.

1. Excitement

This is a common thing that most cyclists do consciously or unconsciously; they get excited during the race and increase their power output above their zone. This often happens during the start of a race; they are feeling energetic and fresh, and as a result, they overexert themselves.

The inevitable result of this extra exertion is that their speed decreases as they feel tired later in the race. So, you need to be careful not to be extra excited as it could lead to a lower Variability index.

2. Ego

Ego is a common problem among not just cyclists but all competitive athletes. Whenever we see someone else doing better, such as someone overtaking us in a race, we increase our speed to match them.

But this decision is often wrong because increasing your speed above your preferred zone will tire you out. You should consistently keep yourself within your zone as much as possible.

Whoever is moving faster than you are either stronger than you or is overexerting themselves. If it’s former, then there is nothing you can do; if it’s later and is at speed above their range, they will pay for it later in the race.

3. Gear selection

Another important thing that needs your attention is the gears of your cycle itself. You need to prepare an appropriate set of gear for your race. If it is filled in with inclines and declines, then you must prepare for that as well. You should get something like a 36 or 34t inner ring or a 30 to 32t sprocket on your rear cassette.

The idea here is that your gears should allow your power output and stress on your legs to remain in your zone even when climbing uphill, even if it decreases your speed. And if other riders overtake you, don’t worry about it; just keep your output in your zone; only in this way will you be able to perform your very best.

Frequently Asked Questions


What is the Variability index?

The variability index represents Variability in your power output during a training session; you can measure it by this formula:

Variability index = Normalized Power / Average Power

What is a good VI Cycling?

The ideal VI during a cycling session is 1, and the preferred range is from 1.00 to 1.05.

How do you calculate Variability?

You can easily calculate your Variability in cycling through the Variability index calculator; type Normalized Power and Average Power in appropriate places and press the button.

What is the formula for Variability?

The formula for the variability index in cycling is VI = NP / AP.


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