I did the exact same cycling circuit twice with a week's interval.
The first time with the HR wrist sensor, mostly in Z2 and a bit of Z3, 2h20 for 64 km => an average speed of about 27.2 km/h, Garmin Connect gives me around 1000 calories actively burned, which is consistent with Strava's estimated power of 128 W average. E (Cal) = P (W) * Time (s) / 4.184 * Efficiency (approximately 25% of energy produced is transferred to the pedals), the numerical calculation gives E (Cal) = 1026 W.
Yesterday, the same circuit but without the HR wrist sensor at an average speed of 28 km/h, Strava estimates an equivalent power output of 135 W average. The formula for active calories given above would result in 1258 calories, yet Garmin Connect gives me 1780 active calories burned, which corresponds to an average power of 200 W while my FTP is at 250 W! This is almost twice the caloric expenditure estimated with the HR wrist sensor !
How does it calculate this? The Strava calculation based on power estimation seems much more reliable.
I don't want to rely on the HR Wrist, as I prefer to have my watch on the handlebars, but this negatively affects the estimation of my daily calories burned.
