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Why do I twice now get a different exercise result for calories burned

Murlin54
Murlin54 Posts: 81 Member
in Social Groups
I have a Fitbit Alta. This is frustrating and not sure if I can explain it. I asked for help a few days ago from Fitbit and the answer was completely unsatisfying. I've been often doing a 45 minutes light jog, followed by 5 minutes of walking to cool down. I also usually spend two or three minutes at the beginning just walking to warm up. My active minutes will usually reflect that in the left column (box) of my dashboard, 50 active minutes. Then my workout in the second column, with the date will say walk, 50 minutes and the calories adjusted. Three days ago, this exact workout gave me the 50 active minutes in the left column but the 2nd column only counted walk 35 minutes. This is the workout I asked for help from Fitbit for. I only paused my workout long enough to take a few sips of water, say less than 20 seconds. I was told this is why my workout stopped calculating exercise calories. I changed my duration minutes from 15 to 10 in the settings to see if it could make a difference. The next day I did the same workout (Wednesday) and it gave me 52 active minutes and column 2 was 50 minutes for 390 calories. Today, I did the same workout again. I made sure to jog for 20 minutes before picking up my water and walking as I took a few sips. I never stopped moving. I started back to a light jog. At the end of my workout my active minutes are showing up as 51 minutes but my walk in column 2 is only showing 35 minutes for 268 calories. What the heck? How can the same workout show different results?

Replies

  • heybales
    heybales Posts: 18,842 Member
    For purely calorie burn, you'll have to look at the HR, not the Active minutes and such.

    Only HR matters in the formula at the moment.
    That produces a calorie burn.
    That rate of calorie burn then allows classifying it as Active minutes (I thought 3.5 x BMR rate of burn).

    If you are relying on auto-start/stop of workouts then indeed HR dropping along with steps would have stopped it.
    If you are manually starting it, it should go until manually stopped or the auto-stop thinks you forgot to, then it'll backtrack to when it thinks it did.

    But outside that - it's all about HR for calorie burn.
    Time obviously matters even if HR was exactly the same.

    Now, Fitbit will adjust calorie burn also based on resting HR, and amount of exercise in a week (perhaps 2 weeks now).
    The formula they are likely using (part of public study so free to use), may have been tweaked a bit over a couple years - but I confirmed the math with several others years ago.

    So yes - there can easily be differences in what appeared to be the exact same workout if say a treadmill on set speed and timer was done. That's why several of us checked years ago, we saw those differences.

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