Cardiac Fitness Score not Improving

[TiffieCatt]

I’m confused and frustrated by the cardio fitness score. I don’t understand how I can lose 10 pounds in a month, reduce my resting heart rate by 8 whole beats, reduce my running mile down by 5 entire minutes all in a month and a half and still have a crap “cardiac fitness score” of 31. My score hasn’t changed since November despite all of my efforts and it’s infuriating and disheartening.

I’m thinking this is on Fitbit’s end. I’ve tried contacting support and received no help. I’ve restarted my device, deleted and reloaded the app, restarted my phone. I don’t understand. Please advise. 

[Gr4ndp4]

Hi, @TiffieCatt, welcome to the community, you may find this article of interest What is my cardio fitness score? which among other things explains how to improve your Cardio Fitness score. There are others here in the community who are more knowledgeable than I am on HR issues, they may have further comments.

Cheers

[LZeeW]

Hello @TiffieCatt and welcome to the Community.  To clarify this from the start, Fitbit's cardio fitness score is an estimate of your VO2max.  The gold standard for measurement has you exercising on treadmill and all of your exhaled air is collected to see how much CO2 you exhale.  Fitbit's algorithm is proprietary, but seems similar to other methods that don't attach you to gadgets.  I'm going to paraphrase Fitbit's Help article a little bit.  If you have two otherwise identical people running side by side, the person with the higher VO2max (cardio fitness score) will have a slower heart rate.  When you are tracking your run to get a precise score, not a range, run smarter, not harder.

Track your runs on ground that is as level as possible.  Run at your natural cadence.  Make sure it's not too hot out.  Make sure you are hydrated when you start.

Here's a link to a V2O max calculator that estimates your VO2max without exercising.  Don't blow it off.  It was result of the HUNT study, a scientific, peer reviewed study.  I can't run like I used to (worn out hip cartilage).  But when I did run, my Fitbit cardio fitness score was very close the to CERG-NTNU calculated number.

[Johnz555]

i think their cardio fitness score is all over the place. I , as an old git of 63 but in good enough condition and decent fitness regime, i had Cardio fitness score of 42 or 43 for last couple of years on the fitbit  , which states excellent for my age, and with a resting heart rate of about 60 i felt good, then in the space of about a month, keeping same fitness workout, its dropped a whole ten to 33....its crap, there's obviously something dodgy in this scoring, basically its broke! so i doubt if your score is anything like that at all as you sound very healthy.  Do the internet guide for VO2 MAX - Max HR divided by Rest HR and x 15.3 , gives youre correct cardio fitness score...

[Gr4ndp4]

Hi, @Johnz555, I've had a steady cardio fitness score for a long time (53-57) and have no reason to doubt the figure. I encourage you to consider @LZeeW's post above.

Cheers

[t.parker]

@Johnz555 Read eexplanation @LZeeW gave above as it's quite compact and does explain a lot. I can add one more thing to it. With fitness watches worn by masses, VO2Max (or Fitbit's cardio score) estimation is often done with the use of different (mostly statistical) data. The problem here is that nowadays majority of people using wearables aren't fit enough (for various reasons) to perform VO2Max tests. As the name states, it's the maximum amount of oxygen your body can consume during high aerobic effort. VO2Max is also called Aerobic Capacity. When you go beyond that effort you are producing energy without oxygen. Now, imagine how hard you need to go to reach your Aerobic Capacity and test it by keeping that level of effort for 12 minutes (Cooper test). Usually, when testing people go beyond their AC and start slowing down until the end of the test and that way achieve maximum distance within 12 minutes which then with a simple formula: 

(Distance covered in metres - 504.9) ÷ 44.73

reveals your VO2Max (and cardio score). It's still an estimation but any estimation based on maximum effort (when you reach your aerobic capacity) is going to be closer to the truth. For example, in my last week's 5k race, if I take first 12 minutes, I covered a distance of 3270m. This will give me a VO2Max of 61.82ml/kg/min for the Cooper Test (and that would translate to Fitbit's cardio score of 61 or 62. Unfortunately, I can't check what Fitbit says now because the app seems to be broken (?) and I can't go to my cardio score (the whole Heart section says "no measurements", not sure why, don't care too much, learned to live with buggy systems of Fitbit).

For people, who don't go into that kind of effort there are other algorithms estimating VO2Max but those will be usually further from the truth. It's pretty much guesswork that is based on comparing certain metrics with a similar sample of the population for which a lab test has been performed. Apple now does that, I believe Fitbit also estimates something that way. Garmin, on the other hand, won't give you any VO2Max if you don't go hard enough and provide reliable data through running (or cycling as VO2Max will be different for different activities).

One thing you may find is that the more athletic person is, the more... ignores VO2Max given by wristwatches knowing that is only a rough estimate (doesn't ignore lab tests though).

"Do the internet guide for VO2 MAX - Max HR divided by Rest HR and x 15.3 , gives youre correct cardio fitness score." - this gives an inflated score for me, I have good reference VO2Max from lab test to compare). This formula is built with the assumption that you know your MaxHR (220-age isn't your max HR). However, even if you know your max HR, the coefficient is based on statistical data and if you are not fitting into that window the error will be larger.

Remember, an estimate is just it - an estimate! 🙂