Connect to Google Fit

Hi there. I need to connect Unity Android App to Google Fitness service. Main goal is to keep track of step count in background and send the data to the server later. Documentation provides two ways – using API for Android app or using REST API.

Question is what shall I chose to achieve my goal? Do I need to install 3rd party native Android plugins to have data sent in background or Google Fit API would somehow handle this itself? Thank you in advance.