Overestimation of calories burned -Fitbit One

[ForecasterJason]

I'm wondering if others have noticed unusually high calorie burns from the device. For me, I tend to think it overestimates my intentional exercise. As an example, on Saturday I jogged backwards. My average speed was 5.2mph, so it wasn't like I was sprinting. My device shows that I burned 50-55 calories in 5 minutes, which means 10-11 calories burned per minute.

I'm only 5'8" 125 lbs, so it's not like I'm a big person. Based on estimates I've seen online of many calories are burned in various exercises, I have a hard time believing that I actually burned that many calories given my size and pace.

Thoughts?

[altat]

I don't run backwards, so can only speculate.  I presume that you have set a step length.  Undoubtably a backward step is a different length than a forward step.  Therefore it may think you are going further in the 5 minutes.  Is the distance it measured accurate?  Just a thought.

[ForecasterJason]

I haven't set a step length, but I do think the step count and distance seemed about right. However, I tend to think there is some overestimation for other exercise as well.

As an example, about a week ago I went walking outside, which included going up a few hills. The distance it said I walked looked to be close enough. Based on that, I was walking at about 3.0 mph. My device showed I burned 35-39 calories every 5 minutes, so 7-8 calories a minute.

From what I've read in various places, over 7 calories a minute is indicative of vigorous exercise, but I thought my intensity was moderate. And although I realize I would burn more calories walking uphill, it's not like I was walking at a particularly rapid pace. I could see if I was 200 lbs, but at 125 lbs this just doesn't seem right to me.

[altat]

In the set-up you tell it your height, weight, sex, step length walking and running, etc.  Are you sure it knows your height and weight?

[ForecasterJason]

Yes, I have all of that set correctly. I have my height listed as 5ft. 8 in. and the weight as 124 lbs. Interestingly though, I don't think my total calorie burn each day is off by a whole lot. Based on my calorie intake, I think it may be overestimating my total calories by 75-100, which would only be about a 3% error margin.

[Tave]

There is bound to be some margin of error with any device.  I also used to think that it gave me unusually high amounts of calories burned.  In the end though I found it to be accurate as, given I increased my calories consumed a bit based on Fitbit's estimates, I am not putting on any weight.  

[Heybales]

7 cal / min is hardly vigorous at all.

That's maybe 6-7 x your resting metabolism. If that much.

That would be jogging 4 mph on level ground for comparison.

Walking on hills could match that.

But, get an accurate known distance - not one that seems right - really check it.

Maybe you got a better feel for distance than most, or me, but that would be unusual for the accuracy you need to confirm.

Then check this - using the Gross option since that's what Fitbit would be reporting.

Oh, and since impact running backwards is totally not what the formula in the device is expecting to use - it should be off. I'd be surprised if distance was really that correct when you went backwards.

http://www.exrx.net/Calculators/WalkRunMETs.html

[DominicJ]

I burn 13-15 per minute at 12kmh

[ForecasterJason]

As for that calculator, I'm not sure of the difference between net and gross as applied to this situation.

I've read that 50-70% of maximum heart rate is indicative of moderate exercise and over 70% is vigorous. I think this may be where the device is overestimating calories burned, since it has no way of knowing my heart rate. I can walk steadily around a room in my house for several minutes, and the device will show that as being 'moderate' calories burned and steps walking as well as active minutes. However, my heart rate is barely elevated from that.

Also, if my device is accurate, I'm still not understanding why several sites I've looked at mention 3.5-7.0 calories per minute and over 7 calories per minute as a rough guide for moderate and vigorous exercise, respectively, if you're saying 7 calories a minute isn't vigorous. Is it that all of these other sites that show approximately how many calories are burned exercising are only taking into account the energy involved in movement, but in reality there is a lot more energy burned from other body functions (part of BMR)?

[SebringDon]

@ForecasterJason

A raw calorie number is meaningless, since a "normal" BMR can be anywhere between 1200 and 2000 calories a day for a person at a healthy weight, and it goes up fast if you're carrying extra weight. First, what's your BMR?

http://www.myfitnesspal.com/tools/bmr-calculator

You'll need to divide your BMR by (24*60) 1440 to get a per-minute BMR.

Then take a look at the table of MET equivalents from the Harvard School of Public Health. METs, or Metabolic Equivalent Tasks, are how you compare the calorie burn rate of various activities. There are far more extensive and detailed lists available if you do a little looking, but this one gives you some basics.

http://www.hsph.harvard.edu/nutritionsource/mets-activity-table/

Multiply your per-minute BMR by the appropriate factor and you'll have a personal per-minute value that should be more useful to you.

My BMR is 1743 calories per day, or 1.21 calories per minute. Very brisk walking has a MET of five. That means I burn about 6 calories a minute at a brisk walk. If I'm jogging at 6 MPH, I'm burning 12 calories a minute.

[ForecasterJason]

Ok thanks. I understand this more now. I think my device is slightly overestimating METs for me, which is causing the calories burned during intentional exercise to be a little too high. I'll keep this in mind for the future.