I just did an 9km run on a treadmill and the machine estimated that I had burned around 850kcal. Garmin connect (Run Indoor function) got the distance quite correct but estimated the energy consumption to be around 650kcal. I have a Strava account connected to Connect which estimated the kcal to 850. I didn't log the run with Strava but it was synchronised with Connect. What explains this big difference and which one is probably more correct?
