I am investigating using HealthKit to supply some data for an application which will run on iOS. We are thinking about using Apple Watch to collect the data. I am especially interested in activeEnergyBurned and some related quantities, namely basalEnergyBurned, respiratoryRate, and vo2Max.
It appears that the sensors on the Apple Watch are just orientation, acceleration, and heart rate. So I guess that the activeEnergyBurned, etc., must be calculated from those items. Can anyone point me to any documentation or other info about how these items are calculated? In particular, any known limitations or constraints would be very helpful to know.
I wasn't able to locate any info about that with a web search. The only info I found that is at all related is this question: How to get Apple Watch 2 to calculate VO2 Max data? Also found this: https://discussions.apple.com/thread/8082402
Are there better articles or descriptions than the ones I cite above to learn how active energy is calculated?