Is my Fitbit cardio fitness accurate?

[MCWalsh]

Hi guys,

I was looking for some help. I am an avid exerciser. I exercise at 3-4 times a week for at least 2 hours a day - usually mixed marta arts, HIIT/running, and weight-based exercises. I also work as a nurse so am on my feet the days I'm not exercising. I usually get my 10,000 steps in every day and meet my max active minute goals. Even with all this strenuous exercise and activity, my Fitbit Versa 2 keeps telling me he cardio fitness is 30 (which is poor for my age of 24). Its been like this for weeks and weeks and it's really gotten my hopes down! Even when I push myself to the point where I feel like I'm going to collapse, I still don't reach my cardio peak. The highest heart rate I can usually reach is around 178bpm. I have hypothyroidism and am on medication which raises my resting heart rate. My resting heart rate is usually 80-90bpm which is entirely secondary to my medication. I was wondering if this has something to do with my cardio fitness, or am I not pushing myself hard enough when I exercise? Any help would be great. Thanks! 🥰

[Guy_]

It may be that recent updates have brought the same instability/inaccuracy [from the Sense and Versa 3] to the heart rate measurement of the Versa 2.

Its not a medical device, so take the results with a pinch of salt.

The original Versa seems unaffected and produces more reliable results still.

That said - Isn't a Cardio score of 30 rather good?

[LZeeW]

Hello @MCWalsh and welcome to the Help forum.  My background is physiology.  In a nutshell, I believe your medication has everything to do with your low cardio fitness score.  You cardio fitness score is an estimate of your VO2max.  Simplified, it refers to the ability of your heart and lungs to get oxygen to your body.  Fitbit uses your resting heart rate and your exercising heart rate to estimate VO2max.  When you expand the cardio fitness score on the phone app, you will find this statement.  "Your score is based on your resting heart rate and user profile."  Fitbit also looks at your heart rate when you exercise.  I am paraphrasing a Help article.  If you have two people of the same size running side by side, the person with the higher cardio fitness score will have a lower heart rate.

Please don't push yourself to the point of collapse.  Exercise to your desired perceived exertion and call it good.  I don't think you should pay any attention to Fitbit's estimate of your cardio fitness score.  Likewise, active zone minutes use your resting heart rate to calculate your heart rate zone.  These zones are never valid when your heart rate is affected by medication.  You say you are a nurse, so you will understand when I say that people on beta blockers can't rely on the cardio fitness score or heart rate zones, either.

I hope this helps.