Hi all
as i have the impression the values my forerunner 245 measures/reports, i.e. spO2 or the calories calculations are not even nearly accurate, I'd like to ask what your experience/impression is?
-- My experience/thoughts --
I.e., on a 1h average 150 Watt ergometer training with average 120 pulse, the watch shows 750 kcal burned. Now, for one hour, my basal metabolic rate is approx. 75 kcal (Harris Benedict formual). So if the BSR is included in the 750 kcal, the active calories burned would still be 675 kcal. Since 150 Watt per second= 0.150 KJoule/s = 0.035.7 kcal/s (divided by 4.2) = 128.57 kcal/h (multiplied by 60 seconds * 60 minutes) and muscle efficiency is approx 23% (meaning only 23% of calories burned go into mechanical power, rest transforms into thermal energy), 128.57 / 0.23 = 559 kcal. So Garmin shows approx. 25% higher kcal.
With walking it's even worse. 3.23km of normal walking on a flat track in 40 Minutes with average 100 bpm, Garmin reports 605 kcals. Again, in 40 minutes BSR is 50 kcal, so we have active calories of 555 kcal. A realistic amount would be around 300 - 350 kcals in ONE hour (there are many scientific papers which have measured this). So here, the difference is astonishing 100% and more! Even more, if we extrapolate this 605 kcal in 40 minutes to 60 minutes, we will get 907 kcal an hour. Now, the 150 Watt/120 bpm/1 hour ergometer training only reported 750 kcal. It's completely implausibel a lower intense walk should burn significantly more calories than a higher intense ergometer training.
These are just two examples of severe inaccurancy i detected. Also i checked the step counter, which sometimes is more accurate, sometimes fails completely (like 100% difference). Remarkably my two smartphones boths are very accurate counting steps. I'm a bit surprised, that smartphones performe so much better than the Garmin watch. I mean, counting steps isn't rocket sience these days.
--
This leads me to a second question: Does someone know how Garmin is calculating active calories burned in a training? Did they made this transparent, publish it?
Happy to read what your experiences are, what you are thinking about accurancy. Any feedback very welcome.
Best, M.
