Hi
The following Apple Support articles offer Apple's advice for checking and managing storage space on your iPhone:
Health data can be exported from your iPhone in the form of XML files, but these are perhaps most useful when importing and exporting data between apps (a health record received as an XML file can be imported into the Health app, for example).
Rather than dealing with XML files, you may find it more convenient to use a third-party app to access, analyse and export Health data to a computer in a more user-friendly format.
For example:
QS Access
SpectaRun Workouts
Check the descriptions and support resources for third-party apps for details of any supported data import / export and analysis features.