Fitbit tracking weights sessions vs entering them after?

So I've been using a fitbit for the past week, and I've noticed something a bit odd-

Last week I did my Monday morning weights session at the gym, and the fitbit told me I'd burned about 500 calories in the hour, with an average of 7 calories per minute. Grand so.

This morning I went in for a really similar session- I had slightly less reps and higher weight but it was a very comparable session, doing the same exercises, same amount of sets, etc. I didn't hit the "exercise" button on the fitbit 'cause I wanted to use it as a timer for my rest periods, and I figured I could just fill in the "exercise" bit afterward.

Today the fitbit is telling me that in that session I burned only 200 calories.

Now, I don't expect every session to be the same, but I did a VERY comparable amount of work this week (a little more, actually- I'm working up from a break so very much getting more in each session) and that discrepancy feels massive to me. To the extent that I'm not sure how to plug this into my calorie budget for the day, you know?

Those of you who use fitbits- do you find there's this much of a discrepancy when you don't hit the button to record the exercise times in advance? I'm using an Inspire, which does have a heartrate monitor.

And also- if there's a discrepancy like that between two VERY similar workouts, which calorie number should I be calculating from? I don't want to ruin my calorie deficit, but I also don't want to be eating hundreds of calories under my budget. As someone who's 5 foot 2, I already have some pretty small windows to work within there!

Thanks for yer help :)


  • Duck_Puddle
    Duck_Puddle Posts: 3,227 Member
    I want to make sure I understand what you’re talking about. The 500 calories is what is displayed on your Fitbit/in the Fitbit app after the workout (if you record a weightlifting session from your watch). The 200 calories is what is displayed in the Fitbit app when you manually log the workout in the Fitbit app after the fact?

    If so-that’s been kind of my experience. When I manually log a workout in the app it appears to use a generic calorie burn number for what I’m entering vs using whatever was recorded by my watch during that time. But-I think it just adds those calories to whatever was recorded by the watch anyway-so the total listed for the workout is lower, but the daily total is inflated (because the watch did actually record the calories burned during your workout-even if it’s not showing a workout).

    If you’re talking about what mfp is showing as an exercise adjustment in these cases; that’s a whole different discussion.

    All that aside-what kind of weightlifting workouts are you doing? Burning 500 calories in an hour doing a weightlifting workout would be highly unusual for a 5’2” female. The 200 number is a lot closer (and might still be high). 500 would be more in line with a solid hour of running-level cardio.

    I know you didn’t ask that particular question-but I figured I would mention it just in case.
  • PAV8888
    PAV8888 Posts: 10,718 Member
    IF I understand correctly hitting the "exercise" button resulted in higher calories.

    Not sure if the "workout" was marked generically or marked as "weight lifting".

    From my understanding hitting the "exercise" button increases the sampling rate on the HeartRate monitor (samples more frequently). Furthermore the whole time is considered as if you are performing the exercise. Otherwise Fitbit detects activity and averages the assigned MET value over 5 minutes increments, assigning a blended MET value on a per 5 minute basis.

    I would expect that your "detected without button" exercise is closer to reality. Though it may, in turn, be an under-estimate.

    This is what it sounds to me as if you were doing: code 02054 3.5 MET resistance (weight) training, multiple exercises, 8-15 repetitions at varied resistance

    The MET value of 3.5 is that for "moderate" activity and similar to "descending stairs" or code 17190 3.5 MET walking, 2.8 to 3.2 mph, level, moderate pace, firm surface

    In other words you would be expected to burn about 3.5x BMR gross calories over the length of the exercise. If you're setup as sedentary on MFP, this would be about 2.25 x BMR worth of net calories.

    You can use this as a sanity check of your values...
  • BeGrandLike
    BeGrandLike Posts: 187 Member
    Thanks so much to both of you! I'm clearly still working out the most accurate way to track my exercise calories, and as I do 3 weights workouts every week it's important to me that I get this one at least in the ballpark of right. Obviously calorie counting is always an estimate, but I'd hate my estimates to be a whole 300 calories off almost every second day!

    Regarding the kind of workouts I'm doing: I'm following a powerlifting programme. So each day is focusing on one of the big 3 (squats, deadlifts, or benching), and then a bunch of accessory work for the other 2. I'm coming back to it from a break of a few months, so my numbers are still pretty low, but that does mean I'm getting more sets in with shorter recovery times. Here's my notes from yesterday:
    Squats 50kg 7 sets of 8 in 15 minutes

    Alternating arm arm db bench 8 reps each side, 15kg each hand
    Band pulldown x 10
    5 sets in 15 mins

    Dumbbell thruster x 8, 12kg dbs
    Inv barbell row x 10, 27.5kg
    Sit ups 12
    3 sets in 10 mins

    The more I think about it, the more the smaller number seems to be closer to reality than the bigger number. It would be REALLY strange for me to be burning 500 calories then- especially when, the day before, the fitbit told me I'd burned ~600 calories in a two-hour skating session.

    I think I'm going to go forward with the ~200ish number. Aside from anything else, I used that to calculate my calories from yesterday and I KNOW if I go too low I'll feel low in energy and irritable, and this morning I'm feeling.. perfectly awake and energetic and calm.

    Thanks again for the insights! Sanity check is much appreciated :D