Extract a zip file and save the content to disc instead

I have to following code snippet originating from the garminconnect python wrapper

activities = api.get_activities_by_date(
            start_date.isoformat(), end_date.isoformat(), 'other')

for activity in activities:
     activity_id = activity["activityId"]
     zip_data = api.download_activity(
                    activity_id, dl_fmt=api.ActivityDownloadFormat.ORIGINAL
                )
     output_file = f"./{str(today)}.zip"
     with open(output_file, "wb") as fb:
         fb.write(zip_data)

It works so far and saves the zip file as intended. But instead of saving the zip file directly i want to unpack it with out writing it to disk and save the content (a .fit file which will be named "activityId.fit" by default).

Ideally i would like to rename it aswell to f"./{str(today)}.fit"

What is fasted and most pythonic way to achieve this?

Thanks for any help in advance!!

import io
from zipfile import ZipFile
    
activities = api.get_activities_by_date(
            start_date.isoformat(), end_date.isoformat(), 'other')

for activity in activities:
     activity_id = activity["activityId"]
     fit_contents = None
     zip_data = api.download_activity(
                    activity_id, dl_fmt=api.ActivityDownloadFormat.ORIGINAL
                )
     with io.BytesIO(zip_data) as byte_stream:
        with ZipFile(byte_stream) as myzip:
            with myzip.open('activityId.fit') as fit_file:
                fit_contents = fit_file.read()

     output_file = f"./{str(today)}.fit"
     with open(output_file, "wb") as fb:
         fb.write(fit_contents)