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Calorie calculation Difference

MACarr
over 2 years ago

Hi,

Struggling to understand why there is a noticeable difference in the estimate of calories burned between rides on my Road bike and on my MTB (mix road & trail).  Here's the data for two rides on consecutive days this weekend.... 

Road Cycling: 25.24mi, 1hr49, 152bpm(av), Zone4=65%, Zone5=7%, 1579cal

MTB: 27.07mi, 2hr28, 153bpm(av), Zone4=51%, Zone5=19%, 1590cal

I'm using a heart rate monitor, and the average heart rate is essentially identical for the two rides.  This implies I am putting in the same effort on both rides, so I'd expect the calorie burn-rate to be the same.  The MTB ride was longer duration (135% of the Road ride), so surely the total calories burned would be about 1/3rd higher. Yet the calories burned for the two rides are essentially the same?

It's almost as if the algorithm is using distance travelled rather than {heart-rate x time}.  Any thoughts?

Thanks, M.

  • 0 over 2 years ago

    The only way to get a reasonable calorie number is to use a power meter. The Garmin produces only a guess at calories when using a heart rate monitor. Not worth looking at since it is way too high. When I started using a power meter, the calorie estimate dropped 40%

  • 0 over 2 years ago in reply to cheracogoff

    Thanks for the reply cheracogoff.  I know people swear by power meters, but I never quite understood how it knows what factor to apply to the work applied at the pedals (the output data from the power meter) to convert that to the work that the body is actually having to expend (ie. calories being burned), ie. to take account that each individual has a different bio-mechanical efficiency.

    I thought that the algorithm referenced statistical data that an average person weighing 'X' kg (which is user input into the Garmin) who's heart-rate is 'Y' bpm (measured by heart rate monitor) is expending energy at a given rate 'Z', and then it summed 'Z' over the duration of the session to give the total energy expended in calories.  Hence why I was confused by the two rides in my example above; I was working equally as hard on both rides as my average heart rate was identical (and I bet if I'd had a power meter on, the time-averaged power for each ride would have been near identical too), yet the calorie burn rate was substantially less for one.

    My only other thought is that perhaps rather than just using Av.Heart Rate over the duration of the ride and a single conversion factor, the algorithm is clever and assigns different conversion factor depending upon which Zone you are in.  My Zone 4:Zone 5 split between the two rides was noticeably different, but that then suggests that the Zone 5 factor (cal burned / bpm) is actually lower than the Zone 4 factor, and that seems a bit counter-intuitive.

    Thanks, from an Overweight Physicist who should really just concentrate on enjoying his riding rather than doing too much maths!!!! Relaxed