When swimming we often do drills (only legs, only one arm, ...) and of course the watch won't be able to know since it can only pick one arm movement. What most swim watches do (like Garmin Swim 2) is they allow the user to manually enter the drill log by marking the start time and end time and then entering the distance covered.
- Can Vivoactive do this too?
Here what Swim 2 does:
www8.garmin.com/.../GUID-A28AE3E4-89B3-41A1-92D5-DAD392C0D5F5.html