What is Fitness Age

When you registered for the PAI Health app, you may have noticed something we call your Fitness Age. Your Fitness Age is a dynamic number, reflecting your current cardiorespiratory fitness level as it compares to other adults of your sex. Cardiorespiratory fitness is how well your heart and lungs are able to get oxygen around your body, also known as your VO2 Max, which impacts your energy levels, sleep pattern, overall mood, and your risk of mortality from cardiovascular and other lifestyle diseases.

The Fitness Age concept and calculator was developed by the Norwegian University of Science and Technology (NTNU). You can read more about the science behind the Fitness Age calculator, including multiple published studies, here.

In the PAI Health app, we calculate your Fitness Age using these metrics:

  1. Resting Heart Rate
  2. Maximum Heart Rate
  3. Age
  4. Sex
  5. Height
  6. Weight

Your cardiorespiratory fitness level, and your Fitness Age, can change over time depending on your physical activity levels - how often you get your body moving and heart pumping, and how strenuous those activities are. This means your Fitness Age can change over time.

How does my PAI Score impact my Fitness Age?

As you start using the PAI Health app, over time you may see changes in your Fitness Age. Specifically, if you routinely earn 100 PAI or more per week, you may see a gradual downward trend in your Fitness Age - that means your Fitness Age could go down!

Don't be discouraged if you do not see a change in your Fitness Age right away. Just like any other lifestyle change, it can take a while. Your heart and body need time to adapt to the progress you're making, which doesn't happen overnight. The app looks at your average PAI Score over the past 30 days to predict your Fitness Age trend, showing you how your Fitness Age could change if you keep up the same PAI Score over the next few months.

Note that you can still see a difference in your overall health, even if your Fitness Age isn't changing and your PAI Score is below 100. If you go from earning 0 PAI per week to 30 PAI per week, you'll still reap some benefits of improving your physical activity levels. It's all about making small changes and working your way up to earning 100 PAI per week, being realistic about your limitations, schedule, and things out of your control.

Is there a maximum / minimum my Fitness Age can be?

Yes - there are some limits to Fitness Age. The 'oldest' your Fitness Age can be is 80, while the 'youngest' is 19. The upper and lower bounds of Fitness Age are based on the scientific database that PAI is built off of - simply put, the research currently does not have enough data for people older than 80 and younger than 19, so at this time the PAI Health app cannot accurately model for younger/older ages.

My Fitness Age is so different from my real age — can that be true?

Yes, your Fitness Age and 'real' age can be quite different. Remember that Fitness Age is an estimation of your cardiorespiratory fitness level - so if you have a Fitness Age of 35, that means your heart and lungs are able to transport oxygen around your body the same as an average 35-year-old of your sex. It also doesn't account for other aspects of fitness like muscle strength, flexibility, or mobility. For example, if you do more weight lifting, your Fitness Age may be higher as your cardiorespiratory level may not be your primary focus. Finally, Fitness Age is calculated using your height and weight along with your heart rate, so it can be higher/lower depending on your BMI.

If you have any other questions about Fitness Age, or anything else in the PAI Health app, don't hesitate to contact us via We're always here to support you on your journey to better health!

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