With the web API, you can only pull data at rest, meaning you'll need to sync your Sense to the Fitbit app before you can fetch the data. The endpoint you'd use to fetch this data is the Intraday Heart Rate Time Series endpoints. If you'd like to test this endpoint, you can do it with the Fitbit API Explorer.    If you're looking to fetch real-time/raw data with 1sec detail level, you'll want to use the Device API and SDK to create a clock face. You can get further assistance from other developers and our moderators in the SDK forum here.

The data is queried directly from your Fitbit account and inserted into Google Fit. To do this, you must first log in with your Fitbit account and give FitToFit access to the data that you want to transfer. You will then be asked to connect to your Google account, into which the data from Fitbit should be inserted.

Sensors API

How to download all of your raw fitbit data

Each Fitbit device includes a variety of hardware sensors that have been exposed through our Sensor APIs.

Unfortunately this is not available via an API at this time.