HRM - Calorie burn varies by day for same workout?

beachk1
beachk1 Posts: 1
in Fitness and Exercise
So I have a HRM (with strap. Polar FT7), and one day it'll say I burn 400 calories for a workout class at a gym, and the next day it might say 325. Now one day I might feel more tired than another, but it's a group class and I'm doing the same or extremely similar moves even though I may hate it a lot more. Why would this vary so much? It's really frustrating because I might do two or three classes, and one day it'll be 875 caloriesand the next day it'll be 650 and I feel like I have to do so much extra work, spend so much extra time, and kill myself to get back up to my target burn. Any suggestions?

Replies

  • editorgrrl
    editorgrrl Posts: 7,060 Member
    The burns are just estimates. Don't sweat the accuracy. All that matters is if you're losing weight or not. If you are, great. If you're not, try eating back half your exercise calories.

    Read this: http://www.myfitnesspal.com/topics/show/1080242-a-guide-to-get-you-started-on-your-path-to-sexypants
  • JeannieFo
    JeannieFo Posts: 35 Member
    I have a FT7 as well and love it! I have noticed the same thing- that my calories burned in the same workout can vary quite a bit. But think about it, are you really working out exactly the same? For me, some days I am better at pushing myself harder than others. Sometimes I am tired, a little under the weather, or stressed and I don't push as hard. I may use lighter weights or take longer rests on those days. I think it's pretty safe to say the no two workouts are exactly the same.
  • MeanderingMammal
    MeanderingMammal Posts: 7,866 Member
    Any suggestions?

    An HRM extrapolates calorie consumption based on how your heart rate varies. It's optimised for steady state or smooth transitions, so the accuracy does reduce if your heart rate is varying up and down at shorter intervals.

    I see pretty consistent measurement for my long runs and tempo runs, but interval sessions can be a bit less consistent. I'd assess that the class situation is similar.

    You've also identified part of the answer yourself, while the session may be similar each day your own ability to perform will vary.

    Any method of extrapolating calorie consumption is an approximation, don't be a slave to the numbers, use them to inform your decision making rather than make your decisions for you.

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