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Calorie usage is way off (and therefor recovery advice doesn't make sense either)

Former Member over 7 years ago

I recently had some problems with my Edge 820 because it simply would not start up anymore. The display showed 'loading maps' and didn't go further than that. With advise from this forum I downgraded the firmware from 9.1 to 9.0 (Actually I downgraded to 8.8 but the device says it is 9.0). After a lot of hard resets I finally managed to fully start up the device again.
Since then it is working fine. The only thing that is very instabile now is the calory usage. This used to be pretty accurate since I am always using a heart rate monitor strap and also a power meter. Depending on the effort (avg heart rate) the calory usage was always between 500 and 800 kcal per hour which makes sense imo. Now the calory usage shows 655 kcal after 2 hours and 20 minutes of riding with an avg heart rate of 120 rpm.
Any tips or advise would be very welcome!

0 nickdodo over 7 years ago

I use 9.1. It all works fine. The first time it loads with new maps takes a long time to start up. After that it’s fine.
Nick

0 mervcharles over 7 years ago

I find the calorie calcultions to be excesssively high. Maybe that is because the 820 does not take into account bike specifics like weight. The calorie count betweren my 510, Fenix 3 and Strava were all within a decent margin of divergence. The 820 averages out at 50% higher. I recall reading that the 820 defaults to a bike weight of 20 lbs. Thats way over the top for my bike and must be what accounts for the errors. Would be better if you could set up bike profiles.

0 nickdodo over 7 years ago

For me the calories in Strava are exactly the same as Garmin connect. I have a Power Meter and the calories will be calculated from the energy used - based on the Power Meter output (and only the PM). The bike weight is not needed for the calculation as as the weight of the bike does not affect the power. HR is not used if you have PM as only the PM affects power. I think the Human body is estimated to be about 25% efficient so Calories burned should approximately equal the total work in kJ.

If if you don’t have a PM then the power is estimated and could be quite inaccurate.

I've no idea what algorithm is used to estimate power if you have no PM and it is this that would determine the Calories