If you struggled and you I would say are fairly fit then I would hate to try this one out. I find once I start running I am ok but that is without hills and obstacles. I am fairly competitive and need to get back into shape first before I even contemplate this.
as i may have mentioned before, there are guys (and girls) that never run, they just hike... as long as they keep moving they normally finish at an ok time because the FRB (front running bastards) like me have to determine where the trail continues. By the time the hikers get there the path has already been set for them, so it is actually a lot easier for the people who don't run. :)