Confused by the calorie counted by the Apple Watch, I used the Apple Watch and Fitbit Charge HR (which I used almost exclusively prior to the Apple Watch purchase) to measure one full day of activity, including a series of fairly intensive gym circuit training including treadmill, spinning and elliptical. I should mention that all personal statistics are correctly entered into the Watch (as well as fitbit) so there is no room for error on that front. Key conclusions:
- Apple Watch total calorie burn was higher than Fitbit by about 250 calories. 3200 cals in the case of the Watch and a (much more realistic) 2925 in Fitbit's case. This is very significant.
- I have long suspected (and a number of people have commented on this in these forums) that Apple's definition of Resting Calories is non-standard i.e. they don't count only the MMR calories as Resting calories. My formula based MMR calculation is 1650 which is very close to what the Fitbit estimates as Resting Calories (i.e. one it assigns to me if I don't wear it at all). However, the Watch's Resting Calories in my case is 2458 which cannot be MMR calories alone. I suspect they include MMR + moderate activity calories in this (see next point) but Apple should clarify this point.
- The difference in Resting Calories is somewhat made up in Activity calories where for almost every workout, Watch would have a lower total calorie (and active calorie count) than the Fitbit's calorie count. For example, a 22 min indoor run showed 285 calories on the Fitbit and 234 Total (and 195 Active) on the Watch.
- The step count is pretty consistent and both measured very similar steps. 10,040 in the Watch's case and 10,232 in Fitbit's case.
Net net, the active/resting definitions need to be addressed by Apple but I am worried about the total calorie measurement. If the Watch is over-stating calorie burn by 8%-10%, that is a very significant error.