How can I convince my girlfriend to go running or cycling with me?

She does exercise in the house using an exercise bike and a wii fit thing, she also does tai chi and zumba cles during the week. I often tell her its a waste of time and we should go running/cycling instead. So I go cycling with a male friend but would really enjoy it if I can get the girlfriend out for a run or cycle on a sunny day. How do you think I can achieve this?