Illogical calorie calculations with BitFit software

[Schwacke]

Hello, I bought a Charge 2 to help me quantify and keep track of my new daily exercise routine. As a starting point, I committed to walking 5 miles a day at a 16 minute/mile pace (it took about 10 days to get there). I also surfed the net to find out how many calories my 180 lb frame should burn at that rate, the surprisingly consistent consensus was about 100 calories per mile.

Now to the point, the FitBit software calculates a burn rate of about 500 calories/mile consistently. When I interface the FitBit with "Map My Walk" I get about 125 calories/mile. Clearly, somebody is wrong, and my brand of logic says it must be FitBit or the weight would be falling off- it's not. 

I can't seem to reach anyone at Fitbit to talk to, can anyone on this message board shed some light on this for me? Thanks.

[Dominique]

If you want to double-check energy expenditure, I would suggest you use standardized metrics (as opposed to "the consistent consensus found surfing the net").

16 minute/mile = a speed of 3.75 mile per hour 

At that speed, it would take you 80 minutes to walk 5 miles

Here are the METs for various walking activities (taken from the 2011 Compendium of Physical Activities😞

The closest to your speed is 5.0 METs. This means energy expenditure performing that activity is five times your BMR.

Now I’ll use this online calculator to estimate your BMR. I’ll assume you’re 40-yo and 6’ tall (does the consensus on the internet know your age and height?).  With these assumptions, your calculated BMR would be 1768 calories. That’s 1768 / 1440 = 1.225 calories per minute (there are 24 x 60 = 1440 minutes in a day).

For the duration of your activity (80 minutes), energy expenditure would be 80 x 1.225 x 5.0 = 490 calories.

Now, are you saying that if you record a 80 minute walk at 3.75 mph on your Charge 2, it claims you burn 500 x 5 = 2500 calories during that activity?! That would be insane indeed.

[Daves_Not_Here]

Here's my opinion:  when you first increase your activity level, you will have a higher heart rate and burn more calories than expected due to lack of fitness (you mentioned it took 10 days to work up to a 5 mile walk).  Fitbit will record the higher heart-rate and increase your calorie burn estimate accordingly.  Your fitness will increase pretty rapidly and your calorie burn estimates will decrease as your heart-rate comes down.

That was my experience -- I used to regularly burn 4,000+ calories per day.  Now, I'm usually under 2,800 even though my activity is higher.  I've been tracking my actual weight loss against what Fitbit would predict, and it's been uncannily accurate.

I'd suggest withholding judgement while observing your results for 30 to 60 days, and you may find Fitbit was more accurate than you may have thought.

[Schwacke]

Thank you very much for your very informative reply. I'm actually 5"8' and 75 years old. The information and references have been very useful. The calorie calculations they provide combined with my actual experience confirms the numbers Fitbit offers are way off. Thank you very much.