SO deadly!
It is weird though, it's so steep that unless you're really pushing your sprint, it feels like you're running on the spot and not exerting any energy. I have to drive my arms really hard just to gain any distance.
I mean, there's a big difference between 400m and running a couple of kms. I have no endurance or conditioning at the moment, so a 5km seems so far to me now... but my partner can punch those out a couple of times a week. Still, I will get the 90!