Cardio Fitness Score accurate?

[emmasawr]

Hi there! I've had the Charge 2 for a few months now (got it back in December) and I've been wondering how accurate the Cardio Fitness score is, and how exactly it is calculated. I currently have a 33 (which is poor for my age) but I don't think I have poor fitness. I'm 19 y/o female and I exercise regularly, as I'm a pretty avid runner. I'm also currently in college living on a big campus, so on a regular day I take at least 10K steps without exercise, and up to 30k with exercise. I run 4-5 times a week, running 3-10 miles per day depending on my training schedule, usually averaging out to 20-35 miles per week. I know the score is based on VO2 max, however, and I do have exercise-induced asthma. My HR to get pretty high during exercise, especially when running up hills (I take a couple of puffs of my inhaler before I go out for runs). Thanks for any insight! 🙂

[Tifayyc]

Thanks so much for your response. So far it's been the only one that seems
like you actually read what I wrote haha. I think you may be right in that
assessment.

[Glaciertrekk]

I think cardio fitness scores with Fitbit are directly related to heart rate, so not very accurate. I, too,  have exercise induced asthma. I live in South Florida and my body does not agree with the heat down here. Back home and cool weather, I can do twice as much as what I can do here. But it’s definitely limited me. But the one thing I noticed with my Fitbit is that my cardio fitness score goes up and down exactly with my heart rate. I’m not even sure that it depends on your resting heart rate as much is just heart rate in general. Because I’ll tell you the other thing is that the more I exercise, my cardio fitness score goes down believe it or not. But it makes sense if they relate it directly to the heart rate because obviously the more I exercise, the more my heart rate goes up. And that’s the trend I see.   Fitbit, as much as I like it, they have a few quirks that they really need to work out.

[JoeC657]

My fitness score now reads 56-60 and I'm 72. Resting heartrate has recently dropped to 46 for the past several days. A few days ago I was able to powerwalk 3 miles averaging 5 mph or 12 minute 0 second pace, my personal best, and this includes 250 feet of vertical on my route. The uphill stretches were very difficult and heartrate stayed below 150. When not pushing for a new personal best, I try to keep my maximum heartrate below 140.

[SunsetRunner]

Do you think that a couple of sentences saying what is taken into consideration to calculate the actual numbers is helpful? They will never dare to show how the numbers are calculated because it will cause lots of questions from the community, especially from the medical community.

[WilsonFitbit]

Hello everyone. @SunsetRunner It's great to see you around. 

Thank you very much for taking the time to provide your feedback. You know Cardio Score is based primarily upon your resting heart rate. This means that as long as your resting heart rate is lower, the better your score is.

I'll give an example: my resting heart rate is usually in the mid to upper 50s so I have a good score but someone resting heart rate was near 90 and that was apparently the cause of the poor score. 

So, if you're receiving a Cardio Score (let's say) between 42/46 and 45/49 and considered "Excellent range", it could indicate that it is well for your age. (As mentioned above), the lower your resting heart rate the better your score is. 

In this case you need to pay attention to your Resting Heart Rate. Resting heart rate is the number of times your heart beats per minute and typically resting heart rate ranges from 60-100 bpm, but the rate can vary based on age and fitness level. 

Also, please note that Heart rate varies from person to person and day-to-day. But if you notice discrepancies with your Resting Heart Rate and Cardio Score, it’s worth mentioning it to your doctor. 

See you around. 

[JoeC657]

I think that you are at least partly correct in your assumption. Fitbit will never show how their calculations are made, for whatever reason, it’s not important. That said I know, from playing around with my stats, your age and resting heart rate are key factors in the calculation. Go ahead and change your date of birth, then check to see what happened to your fitness score.

I have a naturally low resting heart rate, for whatever reason. As low as 48 and as high as 56, depending upon the stress in my life and how well I manage it, including exercise and better sleep habits. Does this make me more fit? Of course not. That is why you can not compare your score with others to see who is more physically fit. It’s not that simple. Use your score to see your own improvements over time, period.

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[WilsonFitbit]

@JoeC657 I truly appreciate your feedback and comments. 

I'm sorry for any inconvenience caused and please note that our team is always working to enhance your experience and your feedback is a big part of that process, definitely it helps a lot and your comments haven't gone unnoticed. 

See you around. 

[BillieJo]

Same here. I noticed my score dipped recently, and I was also just diagnosed with asthma (allergy and exercise induced). After about 2 months of meds it went back up. My asthma is well controlled with steroids and I rarely need to use my rescue inhaler, although my pulse now runs around +5 to 10 from before, and my O2 levels run around -5% from before too. I'm sure it all makes a difference in that score. I'm more interested in the other measurements on my fitbit than this score anyway. If you know you're in your best shape don't let it label you. It's just another tool to use to keep an eye on our health, and these tools are unfortunately not the most accurate. My fitbit (I've owned them all over the years)  has never recorded my heart rate near as well as my chest strap either. 

[WilsonFitbit]

Hello @BillieJo. Nice to see you around and thanks for your input. 

Thank you very much for the detailed information and for taking the time to provide feedback. As you've mentioned, the health metrics including SpO2 are intended for general wellness purposes only and should not be used or relied on for any medical purposes. In this case, it is recommended consult with a health care professional about any questions or health issues. 

Also, I'd like to let you know that you might notice slight variations between your heart-rate reading on your Fitbit device versus on another device (such as a chest strap or another wrist-based heart-rate tracker) due to the differences in technologies. On a side note, for more information about cardio fitness score, you can visit this help article: What is my cardio fitness score?

See you around. 

[jdgRunner]

I’m in my 70s (male) and so have slowed over the years but I have always had a very high VO2Max score. 40 years ago I had a VO2Max score of 73+(I was a 2:35 marathon runner at the time). I’ve had Fitbit for nine months (Sense now) and my score ranges from 53-56, my resting HR is in the range of 50-56, and I average about 20,000 steps and 120-150/day Zone Minutes. To me that VO2Max score seems high since I am now in the range of 55-58 minutes for a 10km. For it to be within 20 of my competitive maximum seems a bit too high (although my weight has dropped ten pounds to 127).

[OldMike]

The VO 2 max is adjusted for age. So as an experiment go into personal
stats and dial your age back 20 or 40 years and see where you stand.

Also bear in mind the algorithm the Fitbit used is formula based. Ie:
divide max heart rate by resting heart rate and multiply that buy 15.3.
I’m 70 a resting heart rate of 54 and a max of 210 so based on the formula
my VO2 max is mid 50’s

[jdgRunner]

How does it determine the various Heart Rates.  I have started to do some real runs, although fairly short.  Four days ago I ran on a paved, accurately measured bike path.  It has about a 1% gradient on the uphill side I ran a measured but moderately quick pace 9:55 Mile 1 and 9:20 Mile 2.  After walking a slow quarter mile I ran 8:12 and 8:08 for Miles 1 and 2 slightly downhill.  Both had average HRs of ~167 with a max of 194 on the Up and 187 on the Down.  The average is a bit low because first minute takes a bit to get up to steady state and sometimes indicating the end of the run can take a bit.  The timing and distance are my own as we have measured the path for UW-Madison Track and Cross Country using an accurate 50m tape and a Wheel.

Then today I officiated the UW-Madison Cross country race and then ran 4 km of the course at 9:25 pace (somewhat thick grass), The maximum HR was 186 but the average was 171.  Do these generate the Max HR score used.

How exactly is the Resting rate calculated?  It is now at 59 having moved into the range of 56-61 having moved up from the low-to-mid 50s (which has corresponded to moving from a Charge 4 to a Sense six weeks ago. [06/05/1950, so your age]

jdgRunner

[JoeC657]

I am a 73 year old male, 5’ 8” 155 lb., not a runner and never have been, but I’m in good physical shape. My best walk/run pace is just under 11 minute mile for 3 miles. That’s about a 34 minute 5k. My VO2 max is off the charts low because of a blood condition. where my oxygen carrying capacity is limited. My Fitbit cardio score is 53-57, Resting heart rate in the low 50’s. It used to be in the upper 40’s when I exercised regularly. I’ve driven my heart rate down to 39 once using relaxation methods a few years ago. I have a great heart rate as long as I am not exerting myself. Strangely, altitude has little affect on me. Sea level or 10,000 feet, there is no noticeable change in breathing while walking or climbing stairs.

In summary, the Fitbit can’t measure VO2 max directly and only approximates the measurement based on resting heart rate, age and weight; things it knows and is not really accurate. Again, as I have stated before, the Fitbit is only a tool that can only be used to show personal progress in fitness and never be used to compare fitness levels with others or yield accurate VO2 max measurements.


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[JoeC657]

I believe that the Max Heart Rate is calculated, not observed, by 220-age. This is not even close for most healthy individuals. That puts me at 147 instead of 185, my actual max. Resting Heart Rate is found by monitoring your heart rate as you sleep. Again, it is not an accurate number because it seems to average my (your) sleeping heartrate from all night, not take the lowest interval as you go through the various sleep stages. Quite often my current heartrate, while on the computer or relaxing, is lower than the stated resting rate from Fitbit. They just can't handle the fact that a 73 year old can have a resting heart rate of 46-50, and I'm no super athlete either. I just have a very low resting heart rate; probably genetic.

This device is far from perfect. What do you want for $100? But they, at Fitbit, have no interest in improving their product either. At least from feedback from long-time dedicated users of the product. I got tired of writing them in the early days and now they are nearly impossible to contact. I gave up.

Take the data with a grain of salt and move on with your life. Best wishes.

[OldMike]

I’ve found the fit bit very inaccurate at higher heart rates. It is a
little better if you can strap it on half wY between the rest and the
elbow. Still for me it’s wildly off ie: manually checking my heart rate by
checking pulse at carotid artery and measure time by the clock on the wall,
I’ll have a pulse rate of 210. The Fitbit will measure it somewhere
between 160 and 175.

I’ve never been able to get my heart rate higher than 210 so I guess that’s
my max. I’m 70 and doing an hour long HIIT routine which is from my martial
arts training. I’ve been doing it for 30 years

[jdgRunner]

For many years (late teens to 40s), my resting HR was 38-42; it was always
naturally low but in my 20s I started running seriously and then switched
to racing on the bike when my foot could not sustain 80-100 miles/week
(marathon PR 2:35, cycling performance similar, especially on hills). In
my 50s, my HR had gotten up to the mid-to-upper 40s. Over time, both aging
and steadily declining frequency, duration and intensity of training
decreased. However, at 64 I had had some good training and my 10km was 45
min, Now I am hoping to hit 56 at 71. By my late 40s I was noticing
continual greenish phlegm which would go away with antibiotics but come
back afterwards; I saw a pulmonary guy and started with an inhaler
including a 'rescue inhaler' that I only take before exercise and which
increases my exercise capability (especially the first summer I took it).

jdgRunner

[kleesklar]

I am a 67 year old female in pretty bad shape trying to recover from long bed rest and deconditioning over the  last 3 months.  Still I get an excellent cardiac fitness score for my age.  Is this an artifact of my low BMI and low resting heart rate of 60?  

[JoeC657]

Yes, it is, exactly. I guess your fitness score will be off the charts high when your resting heart rate goes to zero. Only joking, but take the Fitbit information with a very large grain of salt. It’s a relatively cheap monitoring device to help you evaluate your fitness progress and no way can be compared with any other standard or individual.

Very low BMI is also unhealthy, especially if your muscle mass is lacking, because all that is left is bones and skin. I hope that you are getting assistance from a reputable nutritionist, of which there are very few, and doctor who knows about nutrition, again, of which there are very few.

God bless, and best wishes.

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[kleesklar]

Lol.  I am on the mend and think I’m improving after a bout with long COVID.  I do eat well.   Thank you for your concern!  I’ve gone from walking about 3500 steps a day back up to about 5200.  (A year ago it was about 8000]. It is hard work.  Baby steps.   I love to garden so I’ll probably end up in water prison (during our west coast drought) instead of the hospital.  Best to you, Karen 

[jdgRunner]

I’m not sure about the answer to your question. There is some kind of age adjustment mentioned in the app but I’m not sure what out how. At my best my VO2Max was very high, 73. I was a 2:35 marathon runner who then transitioned to racing on the bike doing long hard hill climbs (my climbing workouts were hard enough that only one of my teammates had a single race on that course that).

I now get between 51-53, mostly 53 for the metric on Fitbit. My heart rate is pretty slow, usually 55-60, and I am 72. I do do some hard workouts, with a goal of running a 10k in 57 minutes, about 9 minutes per mile.

I do not know how much Fitbit uses my hardest workouts and highest heart rates (180).

One possibility is that your low heart rate and possibly low weight (self entered) might fit into the algorithm as well as your history going back more than three months. For me my weight is very low, 125pounds/57kg height 5’9”/1.75meters), and weight is the divisor in VO2Max.

Let me know what you think.

JDG

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