Apple Health on iOS lets users export their entire health/fitness history as export.zip, heart rate samples, step counts, sleep stages, workouts, blood pressure, every recorded metric. Inside the zip is one big export.xml file (often hundreds of megabytes for multi-year users) listing every Record element. Quantified-self enthusiasts, researchers, and healthcare providers all want this data in CSV/JSON for analysis.
How to open
iOS Health app (where it originated). For analysis: convert export.xml to CSV/JSON and load into any spreadsheet/notebook (Excel, Pandas, R).