While global wearable shipments hit an all-time high in Q4 2016, the leader of the market remains Fitbit, although it faced a severe drop in sales. Even this way, the American company managed to ship more devices in 2016 than Apple, Samsung, and Garmin combined.
http://www.notebookcheck.net/Fitbit-shipped-22-5-million-devices-in-2016.200712.0.html