I just started using an Heart Rate monitor for my rides (Garmin Edge 810); but I've noticed the calories calculated for the exact same rides (with and without the HR monitor) are dramatically different (over a 3-fold difference). For example, an identical 45km ride (1h44mins vs 1h48mins) shows I've burnt 1574cals before when I wasn't using a HR monitor; but only 470cal now when using a HR monitor (average HR 112). And I did input my correct age, sex, and weight into the Garmin (is there any other info I need to add to accurately calculate my calories count?). By comparison, using an independent calories calculator, based on my age, weight, speed, time and distance cycled, that ride should have used 1372cals. So I feel the HR monitor is somehow causing the calories calculations to become wildly inaccurate.
I can understand there being some variations when considering HR, but a greater than 3-fold difference is too much. Can anyone help me figure out why the HR monitor is causing my calories calculator to screw up?
Thanks.