We've already had a similar discussion before, right before Fitness went into beta. I personally even moved over from Running to Fitness, because I was expecting them to be merged. Now Fitness is almost 3 months in and I was surprised that none of the top users from Running even have an account on Fitness. Given 81 users are committed, if any of them is also active on Fitness it would have to be less than 18% of them (which is the lowest percentage on the list). Which means at most 15 users could possible be active right now.
I find this particularly strange, because running is the largest tag on Fitness. So either non of these questions are interesting for the users of Running or none of them have noticed these questions or the site. Personally I blame it on our questions rarely reaching the front page of StackExchange.com 'hottest' questions, which seems skewed towards sites with catchy titles or a larger user base. But obviously I might also be wrong in my judgement and wrongly thinking these users would want to participate on Fitness.
So now I'm wondering which of these is it? Is it just a lack of visibility or have the questions currently on Fitness failed to attract the interest of the users committed to Running?