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Calories burn estimation accuracy using HRM

max-au
over 8 years ago
Seems to be a common problem for all Garmin products.

I cycle the same route (50 km, 500 m ascent) two times a week. Same route, same speed, same everything. Including time (1:50). Even my HR is very similar on most days (unless I'm desperate to get to the toilet). But calorie burn estimation varies from 700 to 1200 kcal. To be precise:

* no HRM, no Power Meter: 1250 kcal on average (+- 50)
* HRM, no Power Meter: 720 kcal (complete and utter nonsense, BTW)
* with Power Meter; 1100 kcal (no matter if HRM is connected or not)

Strava reports approximately 1150 kcal, no matter what sensors I use.

It seems like calorie burn is underestimated a lot when HRM is connected (but no Power Meter present).

Did anyone else notice the problem?
  • 0 over 8 years ago
    Must be nice to ride with no wind. I ride to work every day (66km round trip) and my speeds are all over the map depending on wind and how hard I'm pedalling. The 520 is the first Garmin I've used that properly estimates Calories based on power. I'd trust the kJ numbers the 520 uses over HRM based estimates.
  • 0 over 8 years ago
    My HRM Calorie Estimate is Reasonable

    I used to have an iBike Pro (3rd Generation) power meter. It's demise caused me to pick up my Edge 520. I trusted that my normal lunchtime ride (17 miles / 11 km) required somewhere around 500 Calories. On my Edge 520, with a heart rate monitor, it has estimated 450 to 600 Calories (depending upon how hard I work). Without the HRM (sample size, n=1) the Edge 520 estimated 985 Calories. So, the HRM estimate on the 520 is working for me. Typically I've always tools way overestimate energy useage, so this actually refreshingly surprising.
  • 0 over 8 years ago
    Must be nice to ride with no wind. I ride to work every day (66km round trip) and my speeds are all over the map depending on wind and how hard I'm pedalling. The 520 is the first Garmin I've used that properly estimates Calories based on power. I'd trust the kJ numbers the 520 uses over HRM based estimates.


    It's almost circular route, so wind is never an issue. Anyway I've done it so many times that I can simply average numbers and get a decent estimate.

    I see Garmin had implemented following algorithm to estimate calorie burn:
    1. If Power Meter is present, simply convert amount of work (kJ) into Calories (kCal), ignoring any other sensors. It is quite precise and scientifically proven (human body efficiency is ~25%, and 1 calorie is ~4 Joules).
    2. Without Power Meter, but with HRM: count number of beats that heart made and divide it by Coeff (which probably depends on age, weight and height). Ignore everything else - speed, distance, elevation change.
    3. No PM, no HRM: use distance, elevation change, rider weight, age and height.

    Method 1 gives the most precise result.

    Method 2 fails for rider in good shape, but works reasonably good for an average person. I can prove this by comparing my own rides. One year ago it was 1150 kcal (and avg HR ~130), last Tuesday it was 710 kcal (and avg HR 105). Same speed and timer time.

    Can't say a lot about method 3, haven't really tried to collect statistically correct data (as I always ride with HRM).

    This seems to be true for every Garmin device with Cycling mode (tried Fenix2, Fenix3, Epix, Edge 500 and 520 now).

    I wonder if there is any way to fix calorie burn estimation when riding without PM? I don't really want to commute with vector pedals, these are too expensive for city style riding.
  • 0 over 3 years ago in reply to max-au

    So glad you posted this! I was just remarking how when I wear the heart rate monitor, my calorie burn goes to 300 calories an hour where something stupid like that. And when I take it off, it doubles.

    Totally bogus with HRM. I wish there was a fix

  • 0 over 3 years ago

    Additional data point: my calorie count in the 520+ (with cadence and speed sensors, no powermeter and no HRM) increases rapidly if one is coasting downhill, which is ridiculous considering that the 520+ knows the gradient. On the other hand, the total calories for the entire ride (uphill + downhill) is not terribly different from Strava's estimate. So, the device seems to be underestimating the uphill calories and overestimating the downhill calories. 

    There is plenty of room for improvement in the calorie estimates.

  • 0 over 3 years ago in reply to danbarzel

    The same thing happens to me. I used a Fitbit Versa (with HR monitor) and my 520+ . Without the HRM, I get similar calories per mile as the Fitbit & internet calculators using time & speed. Using the HRM, I get calories per mile about 70% or less of the other 2. The Fitbit heart rate is a little higher than the 520, but I think the 520 is more accurate.

  • 0 9 months ago in reply to max-au

    Max-au - Thanks for a great post.  I just used the HRM for the first time and rode 50 miles (out and back route) at 16.1 mph with 1,000 feet of climbing.  I weigh 175 lbs, and at the end of the ride my Garmin said I burned 1,200 calories (average HR was 130 bpm).  Using Method 3, the calories expended should be about 2,500.  I thought I was in some kind of parallel universe.  I will disregard the calorie counter on Garmin from here out.