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The Apple Watch Activity app purports to measure what it calls "Active Calories" which it counts towards its "Move" goal. But Apple's definition of such calories is clearly its own, not counting (at least apparently), for example, calories from weight workouts, Pilates, or yoga or 7-minute workouts?

What is the (Apple) definition of "Active Calories"? What does one have to do to generate them?

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Apple doesn't define active calories in the manual for Apple Watch, but they are a common measurement in sports physiology.

If you are in a coma, your body uses up calories from two of the three muscle types: smooth and cardiac muscle. The third type is skeletal muscle and that's what Active Calories tries to estimate using a physiological model that clearly considers average human statistics and then incorporates input data you feed Apple's Health App (height, weight, sex, heart rate) and then uses the accelerometer to pick apart your specific activity level for input to the model.

Presumably a large amount of PHD level research went into Apple's internal algorithms and models based on who they hired to work on the fitness teams in several internal laboratories.

Since you mentioned some sports, here are my thoughts:

The watch can't know about what weights you are lifting since it doesn't have sensors for that (yet). In fact, the algorithms may mess up since it's seeing your wrist move slowly yet your heart rate goes up much more than it might expect/anticipate. Active calories will be far more accurate for people that run, walk and move without machines or weights attached to their bodies. So pilates (non-reformer), yoga, and 7 minute workouts without weights will be more accurately reflected in Active Calories than will reformer pilates and weight lifting.

Hopefully, weight machines or extra data input can arrive some time later for people to get excellent results with weights. I could see non-free weight machines interface with an app or health kit directly to enhance the recording of your workout profile and progress. Also, indirectly your heart rate will reflect your weight lifting, so without needing specific input, the active calorie measure should still be useful in an absolute measure and highly useful for comparing one workout to another as you add weights and change your metabolic response to physical stress.

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  • Weight workouts? – orome May 10 '15 at 20:12
  • The watch can't know about what weights you are lifting since it doesn't measure that. In fact, you may mess up the algorithms since it's seeing your wrist move slowly yet your heart rate goes up much more than it thinks. Active calories will be far more accurate for people that run, walk and move without machines or weights attached to their bodies. So pilates (non-reformer), yoga, and 7 minute workouts without weights will be more accurate than reformer pilates and weight lifting. – bmike May 10 '15 at 20:21
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    That's very useful information and should really be the focus of the answer. – orome May 10 '15 at 20:28
  • One thing that's not clear: does the widely use term "active calories" that you cite exclude calories for things like weight workouts, Pilates, or yoga or 7-minute workouts, etc.; or is it the sensor limitations you describe that excludes them? That is: would sports physiologists say that the Watch records all "active calories", or a subset of them that it is capable of recording? – orome May 11 '15 at 15:20
  • Weight lifting doesn't happen in a coma, so those calories should be classified as active. How accurate Apple is at estimating them is a separate issue IMO. – bmike May 11 '15 at 19:33
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Using a heart rate monitor like the polar Bluetooth model makes the difference. The heart rate monitor on the watch by itself is let accurate enough, but with the strap it's pretty spot on.

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  • try to shift your answer more towards the question - there was no interest in heart rates, but in Active Calories. – rwenz3l May 10 '16 at 12:32
  • Anecdotal, yes, but this morning I spot checked my watch's heart rate measurements during a workout on a Precor 576i elliptical. The watch and machine were either the same or off by one or two beats per minute. Either they're both inaccurate in the same way or they're both accurate. The former seems less likely to me. – bmauter Dec 7 '16 at 14:40

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