Google Fit has a range of health data that you record / collect for months or even years using your phone, so it's important to back up frequently. With Google Data Takeout, Takeout, you can export a copy of Google Fit data in minutes. See how you can use it.
Go to the Google Takeout website and sign in to your Google Account. Click the "Deselect All" shortcut if you are only interested in Fit and do not want the file to contain copies of your data from the rest services of Google.
Look for "Fit" in the list and select the box next to it.
Click the "All Fit Data Included" button to select whether you want to back up your data activities your daily summaries of sessions or both. The "Multiple Formats" option will tell you in what format Google will archive your data in Fit.
Now, scroll down to the bottom of the page and click the "Next Step" button.
Once you have completed the customization of these settings, select “Create Export”.
Google will start exporting a copy of data to Fit. You do not have to wait, as Google will notify you by email when it is finished. Depending on how much data you have collected in Fit, this can take days or even weeks.
You can also cancel your backup request by selecting "Cancel Export".
When Google completes creating one copy of your data, you will receive an email with the subject, "Your Google data is ready to download".
In this email, click the "Download Your Files" button to access your archive file. Sign in again with your Google credentials for confirmation.
It will redirect you to the "Manage Your Exports" page and the file will start downloading automatically. Otherwise, you can manually grab the file by clicking the "Download" button next to the Fit export entry in the list.
The downloaded ZIP folder will have a "archive_browser.html" document that will allow you to easily read all the health data. You will not be able to read it directly information, because the files will be in TCX or CSV format.
With Takeout, you can also export data from other Google services, such as gmail.
Source of information: howtogeek.com