You could create your own, but I assume a post can only be in one. One issue is that apps like Actifit and Exhaust will not support posting to communities for a while, but people could put their general running posts in the community. It provides an alternative to resteeming as you can follow the community instead. We will have to see how people use them. I think they offer some moderation features and you can appoint admins.
I have walked up Ben Nevis and that was hard enough. I have run up some hills around Edinburgh when I've been up there. That's a good workout.