Suunto brings both halves of the incoming data into Coachbox: the workouts your athlete records, and the numbers their watch collects the rest of the day. Once the account is connected, neither of you touches it again.
What arrives
Finished activities land in the calendar with all their data behind them, so pace, heart rate, power and GPS are all there when you analyse the session.
Daily metrics come across as well. If Suunto is the watch your athlete actually wears around the clock, set it as the metrics source and steps, resting heart rate and sleep follow from there. That choice is separate from where your activities come from: your workouts still arrive from whatever device recorded them.
What does not
Suunto is read-only in this connection. There is no route from Coachbox to a Suunto watch for a structured session, so your athlete opens the session in the Coachbox app and follows the blocks there.
If automatic delivery to the device is a requirement for that athlete, Garmin, Coros and Wahoo all take a structured workout.

