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Helpful answers
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Apr 20, 2016 11:12 AM in response to Doug Eldredby Jonathan UK,julie78787 wrote:
As nearly as I can tell .. "active calories" are determined based on heart rate, weight and percentage body fat. Those need to be entered on the "Vitals" screen
To clarify: this is incorrect.
Body Fat Percentage does not need to be entered in the Health app in order for Apple Watch to estimate Active Energy (calories / kilojoules).
When estimating Active Energy, Apple Watch uses the personal information that is supplied when setting up the Activity app (along with any other relevant data sources that may be available, such as heart rate). Personal information can also be edited over time:
- On your iPhone, in the Watch app, go to: My Watch (tab) > Health - check and Edit (upper-right) Birthdate, Sex, Height and Weight.
If using any other health apps that share weight information to the Health app over time (for example, Health Mate by Withings), any changes to weight data will also be updated in the Watch app.
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Apr 20, 2016 11:21 AM in response to Doug Eldredby Jonathan UK,julie78787 wrote:
The Watch measures strides by looking for regular changes in accelerometer readings. From those measurements it infers -- indirectly -- that you've made a single step.
.. the Watch is guessing based on the calibration which was done, and as you've found your stride length (and mine ...) changes with speed.
Apple Watch seeks not only to identify when steps have been taken, but also to estimate distances travelled, including adjusting those estimates to reflect different walking and running speeds.
Calibration teaches the watch how your arm movement relates to your stride lengths at different speeds. It does this by combining knowledge of how your moves (using data from the watch's accelerometer) with knowledge of actual distances covered (using the Location Services / GPS feature on your iPhone).
More information:
Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support
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Apr 21, 2016 3:05 AM in response to Jonathan UKby Chris J Davies,Although the initial calibration was a pain to complete, since doing that I have been amazed at the accuracy of the Apple Watch in tracking treadmill runs. I typically do a 5-6KM mix of running and walking an a daily basis on a treadmill. Before calibrating I was seeing a difference of up to 1.5KM! After calibrating, the watch and the treadmill are now always within 50 metres of each other by the end of a 5.5KM session. That leaves me very impressed.
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Apr 22, 2016 1:02 AM in response to Jonathan UKby julie78787,Jonathan,
I don't know that Apple has released the algorithm used to calculate Resting Energy.
http://www.nature.com/ijo/journal/v24/n9/full/0801317a.html
"Fat-free mass (FFM) is the single best predictor of resting energy expenditure (REE), explaining much of the inter-individual variability in REE.1,2,3 Some investigators report that body fat is an independent predictor of the inter-individual variation in REE,4 which is logical considering that adipose tissue consumes oxygen at a rate of 0.4 ml/kg/min.5 This rate of oxygen consumption is much less than that for lean tissue,6,7,8 and suggests that large numbers of subjects must be evaluated in order to detect an effect of body fat on REE in cross-sectional population studies. In addition, robust methods for measuring body composition and REE must be employed. A significant portion of the inter-individual variability in REE remains unexplained even when FFM and fat mass are known, however."
Since we last chatted I have found that the Fitness App miscalculates "Resting Energy" during workouts by about 50%. I did a 4.38 mile walk this evening for 1:07:14. Active calories were 369 and total calories were 488. The difference -- 119 -- equates to 2,557 total resting calories. According to the Health App my resting energy yesterday was 1,821 and my active calories were 658. The total is 2,479. A resting energy of 1,821 calories per day is 1.265 calories per minute, so the correct resting energy during that 67 minute stroll should have been 85 instead of 119.