Jack Morris
Inspecting Fitness+
Dec 15, 2020

Whilst trying out Fitness+ I had a thought for a quick app - some form of Fitness+ companion that summarized what workouts you'd done, your favourite trainers / activity types, etc. The Fitness app surfaces the specific workout that was performed, so I wondered whether Apple had snuck something into the HKWorkout's metadata to link back to the workout somehow.

Alas, as far as I can tell, no luck. Here are the metadata dicts associated with my two most-recent Fitness+ workouts:

Workout metadata: [
    "HKTimeZone": Europe/London, 
    "HKWeatherHumidity": 8500 %, 
    "HKIndoorWorkout": 1, 
    "HKWeatherTemperature": 35.6 degF, 
    "HKAverageMETs": 6.22975 kcal/hr·kg
]
Workout metadata: [
    "HKTimeZone": Europe/London, 
    "HKWeatherHumidity": 8500 %, 
    "HKIndoorWorkout": 1, 
    "HKWeatherTemperature": 35.6 degF, 
    "HKAverageMETs": 8.85041 kcal/hr·kg
]

I'm guessing they're using a separate service to sync Fitness+ progress, since this history is also partially visible within the Fitness app on iPad (which doesn't have HealthKit). Associating the UUIDs of the corresponding HKWorkouts there would then allow them to do the rich workout association on iOS in the screenshot above.

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