FitBit Versa 3 Calories too low for spinning activity

[jonahmb]

I did a two-hour long stationary bike ride this morning, and my Fitbit's calorie count for it seemed quite low. It felt pretty difficult. My average HR, as can be seen was 117BPM, and I peaked at 137. I'm about 50kg. Is 500 calories an accurate amount burn for an activity like this? I would imagine a much higher value. I genuinely would have burned more walking. Something is seriously wrong. My spinning activities have always seemed abnormally low (ie 300 cals for 1 hour), but this is something else. 

[JohnnyRow]

First, I'm so much heavier than you, I can't begin to judge what a reasonable calorie burn rate might be at your weight. But I would not short-change faster walking as a calorie burning activity; I have sometimes been surprised at the calorie burn rate of walking compared to the apparent effort vs. other activities.

But also, I noticed that your heart rate never was getting into the aerobic zone, getting into fat-burn during high-effort periods, then down into below-zone cycles.  I wonder if it possibly could be that for particular activity, for you it just feels more difficult than the actual load it is putting on your body.

I really don't know - just guessing at possibilities here.