I guess it depends how you're adding the treadmill activity. If you let your tracker track things then you'll get a distance measure automatically so that's probably the best way.if you're manually entering data, however, then you're limited to whatever the system allows you to enter. If that doesn't get added o your total automatically (and I can't remember exactly what gets added where anymore) then there's nothing you can do about it.
if you let us know what you're doing and what the result is, that may help us get closer to a better answer.
Mike | London, UK
Blaze, Surge, Charge 2, Charge, Flex 2 - iPad Air 2, Nokia Lumia 925 (Deceased), iPhone 6
Take a look at the Fitbit help site for further assistance and information.
