I have the same problem. It's really hilly here and I can see that the Spark calorie counter is only calibrated for actual speed, which can be actually quite slow if the hill is very steep.
I bought a Garmin Edge and it seems to slightly adjust the calories depending on the "feet of ascent", but even that isn't very accurate.
Whenever I have a day of hill climbs, I'm always disappointed by the calorie burn which is based on my slow speed rather than the effort.
The only way to keep your health is to eat what you don't want, drink what you don't like, and do what you'd rather not.
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