[Tangurena]

Hmm, this is an interesting idea. Perhaps instead of making the buff wear off, make things available for the next time you are "in game" as it would be rather risky trying to play the game while walking on a treadmill, bike or eliptical machine.

[Grantmd]

That's a good alternative. Although I think the game would be easily playable at even a quick walking pace on the treadmill, they could trade each minute on the machine with a minute of the buff next time you login. Or charge up an orb in your inventory that you can use at will.

[eru]

Just make sure that you can't make other people walk for you. (Or do make sure that you can?)