Calories burned are incorrect - too low for some activities

[porcelina]

HI all,

I am a new member and looking for some help.

I have been tracking and logging fitness and food for many years now via sparkpeople.com. I also used to use a polar hrm for tracking calories burned when I was initially losing weight around 4-5 years ago. Neither of these had the same level of detail as the fitbit, and so I am still getting used to everything and figuring out how it all works. However, I am getting a bit perplexed!

At my goal weight (139 lbs) according to my HRM, I was burning about 400 cals on a 30 minute run and around 600 for an hours high intensity circuits class, sometimes 700 for Body Attack. Spark people would give a lower cal burn because it was more of an estimation than an accurate reading. 

I have been using my fitbit charge hr now for around a week - I have worn it for a 32 minute run, during a 45 minute Body Attack class and then for GRIT strength and CX worx this morning. Each of my burns seems a little low in my opinion: 169 for GRIT, 341 for my run, 356 for Body Attack.

The run probably makes sense to me as it was a gentle run as I am getting over a chest infection, however the gym classes don't. I don't wish to blow my own trumpet or sound conceited but I worked really hard - and always do - in GRIT and Attack. Also, a lot of my friends have fitbits and their burn was a lot higher than mine, and we were all pushing equally as hard together!

I am wondering if I have something set up wrong, or if I am using it incorrectly? The polar unfortunately is broken and it was a couple of years ago when I was using it, so it could be that over the years my body has gotten used to working at high intensity during these activities and so I don't burn as much - however I still feel just as pooped at the end of the sessions as I used to do!! Maybe I need to find some more intense workouts!

Any help would be gratefully received. Thank you.  

[Mike007]

Seriously?

[Veryberrystyle]

I also bought my Fitbit hr 2 in January brand new so it’s not faulty 

[phatbitzr]

I tried getting calorie counts 3 ways on a Lifecycle stationary bike w/watts output, 2 via Fibit and one via the bike.

Riding at 300 watts output (a standard way of gauging cycling performance), as displayed by the stationary bike.

The stationary bike displays around 1300 cal/hr

My HR at that moment is around 158 and the calorie rate 12.5 cal/min, which comes out to 750 cal/hr

Manually entering a spinning activity for 300w (there is no 300w, so adding 100w+200w gives 1094 cal/hr, and 150w+150w gives 958 cal/hr)

Websites generally converts 300w to be around 1100 cal/hr, based on a conservative 24% energy conversion rate.

So manually entering the information could get you in the ballpark (except nobody rides at a constant power output for the whole duration), but I am not sure how accurate if it relies purely on HR.

What happens if a person in better shape pushes out 300 watts with a heart rate of 145, the calorie burned based on HR would show them to be even lower than the already underestimated 750 cal/hr.

[Mike007]

The fitter you are the lower your HR the less calories you burn. Your Fitbit will be the most accurate of all your examples.

[phatbitzr]

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@Mike007wrote:
The fitter you are the lower your HR the less calories you burn. Your Fitbit will be the most accurate of all your examples.

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This goes against almost every study I have seen.  the MET value specifies energy expenditure is independent of how fit you are, and calorie expenditure value derived from the MET value should only take weight into consideration.

An example, if my V02max increased 50%, and I now work out at the same HR as before, near my LT, which would both feel like I am at my limit.

Even without knowing the power output of the 2 exercise sessions, where is the extra 50% of oxygen my body is using up going to?

If you are implying at both fitness levels,

given the same HR, they both will burn the same number of calories,

then where would I be able to utilize the 50% increase in V02max?

I don't think my HR has the capability to beat 30-50% faster.

[SunsetRunner]

Fitbit won’t admit this (and may even remove this) but wrist mounted heart rate monitors are not designed for hiit training. Something monostructural like running is better because it’s limited range of motion (relative to hiit or weight lifting) and usually your hands are raised or at least parallel. This leads to less sweat between the wrist monitor and the skin. Since wrist mounted HRMs measure using light, the sweat can throw it off. Chest straps measure electrical activity so sweat may actually help measure heart rate more accurately. On top of that, the constant changing motion of hiit and weight lifting will move the Fitbit around, removing the connection required to measure heart rate, which is why it’s usually “behind” when you raise your wrist, and allowing sweat between the Fitbit and your skin. It’s a pain but a problem with all wrist mounted HRMs. Which is why apple watches allow you to connect a chest strap for working out. Honestly I’d use the numbers and stick to your diet and monitor your weight/body fat, then adjust accordingly. Annoying but it’s what we have right now.

[Julia_G]

@SunsetRunner, I would be astonished if your post were removed.  If in doubt about what is allowed, please see the Community Guidelines

In fact, Fitbit openly admits that certain exercises can make it difficult for the wrist mounted HRM to work as accurately (although not necessarily from sweat -- wrist movements may also be an issue).  From the help article What should I know about my heartrate data :

"With high-intensity interval training, P90X, boxing, or other activities where your wrist is moving vigorously and non-rhythmically, the movement may prevent the sensor from finding an accurate heart rate. Similarly, with exercises such as weight lifting or rowing, your wrist muscles may flex in such a way that the band tightens and loosens during exercise. Try relaxing your wrist and staying still briefly (about 10 seconds), after which you should see an accurate heart-rate reading. Note that your device will still provide accurate calorie burn readings during these types of exercise by analyzing your heart rate trends over the course of the workout."

They do state that they should be able to get an accurate calorie burn over the course of the workout, but obviously if ALL or MOST of your workout involves activities in which an accurate heartrate cannot be determined then it is likely, in that case, that it will give you an estimate that is incorrect.  For certain workouts, if you really feel confident of the calorie burn it may be better to create a manual log . A manual log will overwrite what your Fitbit calculates during the same time period.

[CatBerge]

Today I biked 4 hours, 100 km, and my daily estimate now at 6 pm is 2400 kcal, 59 kg very athletic build

[CatBerge]

so, today i rode 100 km bikeride, and my daily calorie estimate is 2300, and it is consistently very low, I eat way more than what it estimates and I do not gain weight

[CatBerge]

my research is that I eat way more than fitbit estmates and I do not gain weight. Fitbit underestimates my daily calories with close to 1000. kcal 

[LisaMoore007]

I’m having the same problem. My Fitbit is registering calories burned at 1200 when that’s lower than my BMR! And on days I’m doing 90 minute workouts. So weird and frUstrating. 

[Starbuckxvi]

Yep. Same issue here. It’s discouraging but I keep telling myself I am too obsessed. Maybe the uncertainty is good for me 🙄 still I wish they would fix their algorithm 

[Sueiyinh]

Yeah I agree, the watch/tracker should be manufactured to withstand these activities - afterall that's what it is designed to do - to accurately monitor certain measurable physiological changes during exercise. I'm not sure why it is just not able to accurately read this, it's stumped me too!!

[lazydaisy84]

Same happens to me! Only worse: I've just completed a Body Combat class, which is usually an hour long and really intense (heart rate in the peak zone and everything), and my Fitbit says I burned a meager 40 cal! There's no way this is accurate. What can I do to fix this? Did anyone find a solution?

[calrenbowie]

For one, make sure your Fitbit is 3 fingers on your wrist and you can see
your heartbeat on the watch. If your watch is not sensing your heartbeat
it will not sense the calories.

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Moderator edit: personal info removed

[lazydaisy84]

I had read this same advice on the user manual and made sure the watch was three fingers away from my wrist bone before the class started. Maybe it moved while I was jumping, punching or kicking away? Like I said, it's a really intense class and I make sure I give everything I've got. I'll double check next time and report back. Thanks for the suggestion.

[calrenbowie]

Also, make sure your heartbeat is registering. I can look at my watch
and see what my heart rate is. If you can't do that (depends on your
watch) then check on the app. If it is not registering you need to figure
out where it needs t to be or the heart rate may not be working.
Hope this helps.
--

A charitable, cause-driven organization working for community well-being.
The Y. For a Better Us.

Moderator edit: personal info removed

[jsr]

Having the same issues. At first my fb burned 300 cals in a barbell or other class. Now they are all half that. My bpm are low too. Compared to my friends fb in the same class mine are low. Ive restarted etc but no changes. Im tired of the inaccuracy bc this is my 3rd fb and its really important for me to track accurately. Please advise fb!

[Melhopper21]

Five years later and this still seems to be an issue with Fitbit. 😞 

[CatBerge]

Indeed, and after several new versions and upgrades they are still far off in calorie burn. They seem to i sinuate that a woman of 57 kg and about 165 cm walking about 10,000 steps per day burn less than 2000 calories.