One vs. Flex 2 Calorie Burn

xLyric

I've been using my One for over a year and was given a Flex 2 by a family member, and I've been using them both to see which I want to keep. The Flex 2 is surprisingly close in step count to the One; it's maybe 50-100 steps behind the One at the end of the day, which I'm impressed by. I was expecting it to exaggerate steps because of arm movements, so I'm happy there.

The calorie burn is confusing, though. Yesterday, my first full day having the Flex, here are the numbers:

One:
Calories: 2,668
Steps: 13,419

Flex:
Calories: 2,790
Steps: 13,394

My stats are almost exactly the same on both accounts. The One is connected to my Aria, so the weight on that one differs by maybe a pound. That's the only difference I can find.

Why is the calorie count so far off? That's a whole extra snack for almost the same amount of steps.

Edit: I should probably clarify; I'm looking only at the end-of-day calorie burn total on Fitbit (not MFP). No adjustments or food are coming into play here, just the daily totals by themselves before any deficits are looked at.

heybales

Steps are used in calculating calories - so the fact they see about the same amount is good.

But steps becomes distance, and with time becomes pace - and that and weight is what calculates calories.
So if the impact of the steps is seen different, the distance becomes different.

So how is the distance in comparison?

Also, that is only a 122 cal difference - which is only a 4.5% difference.

You have potentially more inaccuracy allowed in your nutrition labels, and in fruit depending on ripeness compared to database entries.

And yes, that lb difference can matter about 50 calories, purely from the BMR and activity aspect.
The impact to distance calculations are using weight as a factor.

It's why wearing heavy clothes and being very active daily can give deflated calorie burn values.

xLyric

I hadn't thought of distance, but when I compared the two for that day the One had me as having gone .02 miles further, despite having the lower calorie count. I also checked the weight difference, and I was mistaken; it's not a pound off, it's .1 pound off (216 vs 215.9).

You're right, it's definitely not a huge deal in the grand scheme of things, I was just hoping to find whatever was causing the difference. Especially since for Friday the Flex is still about 100 calories over the One, but this time it's actually got a decent step lead since I wore the Flex longer. That would make it seem like it was working correctly, if not for the fact that it gave me an extra 122 for walking less the day before. So, Flex has more steps than One=more calories on Flex, and also Flex has fewer steps than One=still more calories on Flex. It's just weird.

Don't get me wrong, I do think the Flex is doing its job correctly, I just clearly don't understand the calculations as well as I thought I did. I don't usually eat them all back anyway, so I'm just not going to worry about it, haha. Thanks for the help.

heybales

So that is more useful info to compare at least than steps, which is merely the stat to get to the ones that matter.

You could try to track it down as to figure out which is more trustworthy.

I know one person I helped narrowed it down to some extra false steps on one device, and while it gave minimal distance and calorie burn for them, it caused the difference.

I've had days where a run caused almost the same total as a day with lawn mowing for steps and distance, but the calorie burn for the run was more. In that type of case the Fitbit couldn't see the extra effort of pushing a mower, merely the smaller step distance and slower.

So there are reasons behind the differences. And if I pushed mowed daily as work - I'd probably want to figure out how to make it more accurate.
But weekly for 45-60 min just doesn't matter in the scheme of things for the week, even if the day is a tad off.

Some activities and movements will just cause differences going one way or another.
Since it automatically causes under-reporting of calorie burn (it doesn't add in the 10% calories burned for processing food eaten, nor the extra burn of standing which is given sleeping rate burn, nor being awake sitting which is more too) - any differences causing inflation aren't usually that bad.

xLyric

Yeah, that makes sense. The answer I got on the Fitbit boards was basically that the Flex 2 is newer than the One, and so calculates a little differently (hopefully better). Either way, I'm not going to stress about it anymore, haha. Thanks!

VioiletAgnes

I have been using the Flex2 for swim laps of aerobic running. The Fitbit calculated time for my weight in the pool was 75 calories; the same time under MFP for swim aerobics is 334. Why such a difference in calories burned?

heybales

Because any step-based workout given a calorie burn is based on formula for walking level ground.
Based on steps seen, calculated distance covered, and time and weight.

And you were no where near where that walking formula could be correct.

Your impacts, if even all seen which likely they aren't, were probably very short distance because of being light since not full mass.

Just wrong tool for the estimate. So correct to manually log.

That's true for any non-HR Fitbit which will use step-based calorie burn, if doing non-step based workouts - swimming, rowing, elliptical, lifting, stairs, climbing, bike, ect - must be manually logged.