fitbit VS. Polar FT4

[dawnhp1971]

My fitbit is showing more calories burned than my Polar FT4, how is this possible?

[slysam]

What was the activity? what type of fitbit do you have and where do you wear it? I don't see why it would be considered impossible. Both are giving you estimates (not direct measures) of calorie burn based on different data. In a lab, calorie burn is usually figured from oxygen use.

A heart rate monitor's calorie burn estimate is usually estimating oxygen use then estimating calorie burn. Each company has its own formula, so if you were to wear two hrm's you might get different calorie burns (I have out of curiousity). Most hrm's use some variation of the workout's "average heart rate" and compare it to your entered "maximum heart rate". It usually estimates the oxygen use from what percent of your max heart rate your average heart rate reaches (i.e. 60%, 80%) and somehow plugs that into a formula to estimate calorie burn (my current most-used HRM, the app Digifit I cardio has published their formula so I know what it uses). HRM's calorie burn estimates  are usually best for steady state aerobic exercise where your heart rate is within your aerobic zones and stays similar throughout the workout. With intervals of step based cardio, my fitbit will sometimes give a higher calorie burn than my HRM but that will vary depending on how fast your heart recovers (as fitness improves recovery often improves) and the activity.

My first HRM use to give me a lower calorie burn for the same workout if I included the warmup and cool down than if I started the workout timer after the warmup and ended it before the cool down. Like somehow the extra 10 minutes of warmup/cooldown burned negative calories. Well, it didn't, that was just a flow in my old HRM's formula. I've not seen these issues with my old polar hrm or the app I use more often (Digifit).

Another thing that can amke a difference for the calorie burn is your maximum heart rate. If you didn't enter one, it is usually estimated from a formula. Age and sometimes gender are the big factors in the formulas. And they often estimate high or low for a significant number of people. According to a book I read on heart rate monitor training, maximum heart rate is largely genetic and the extent it declines with age varies a lot especially not that more older adults are keeping fit and active. One sign if it is set too low is if you routinely go above your maximum heart rate while barely breaking a sweat. It is suppose to be a level you would rarely reach and only sustain a short time (the fastest your heart will currently beat in normal circumstances). This person might see crazy high burns in relation to their other stats and effort. On the other hand, some people tend to have slower heart rates so they may have to work very hard to in theory reach their aerobic zones (maybe will even be out of breath--which is a sign you exerted more than aerobic levels). Those people might have very low calorie burn estimates compared to peers (I am one of them).

It took me some trial and error to get my zones/maximum heart rate to a point that I feel reflects my exertion. After getting there, it is pretty rare for my fitbit burn to be higher than my HRM, I only see it for slow walking (that doesn't get my heart rate in aerobic zones, once it does both fitbit and my hrm are within a couple calories), and the elliptical if I use no resistance settings (add a little resistance and they match or are close). There are lots of activities where my HRM gives a higher estimate (mainly non-step or resistance activities) and quite a few where they match or are within about 20 calories of each other.

[Heybales]

You don't give enough details.

Both are estimates though, and both can have better accuracy for some exercise/activity, and both can have terrible accuracy for some exercise/activity.

HRM formula for calorie burn is only valid for steady-state aerobic exercise, same HR for 2-4 min in the aerobic zone from 90 to around 150-170.

Anything non-steady state (intervals, lifting) or not aerobic (sitting around, or lifting, intervals) is going to be inflated.

Fitbit is using great calculations for step based exercise, walking formula more accurate than HRM actually.

Anything not step based (lifting, swimming, spin/bike) is going to be badly under-estimated.

You'll have to look at what you are comparing and decide.

Besides the fact the cheaper Polars make big assumption since they are missing a vital stat - VO2max.

They assume if your BMI (height & weight stat) is bad for you (age & gender stat), then your fitness level must be bad - so lower VO2max is assumed.

And even with lab measured stats entered in the watch, it can still be off up to 5-15%

http://journals.lww.com/acsm-msse/pages/articleviewer.aspx?year=2004&issue=08000&article=00024&type=...

Here's study on the walking/running formula's being within 4% of accurate.

http://www.ncbi.nlm.nih.gov/pubmed/15570150