To save battery when exercising, some of the battery modes in Suunto 9 change the interval of the GPS readings. To avoid getting bad GPS tracking when exercising Suunto 9 uses FusedTrack. FusedTrack uses motion sensors to log your movement between the different GPS readings, which will provide better tracking of your exercise.
FusedTrack is activated automatically during running and trail running when Ultra or Endurance battery mode is chosen and it improves the tracking and distance accuracy between the GPS readings. Endurance mode uses a GPS reading interval of 1 minute and Ultra mode a GPS reading interval of 2 minutes.