Obstacle Courses & Motivation

In my area in the fall seasons, there are a lot of marathons. There is one call the Darby Run. You have three options- just 5k, just obstacle course, or 5k AND obstacle course.

I really want to do the obstacle course, but not sure how to train my upper body. I'm not very strong in my arms, and wanted to know how the best way to do it and how do it semi quickly (safely). There are a lot of monkey bars and pulling your weight on the obstacle course.

I have a little over a month to prepare. Any tips, feedback?

Also, I really need motivation to stick with my workouts. I walked/ran 62 miles in August, and want to do the same/more for September too. I just need more motivation. The scale is only making things worse for me ... not seeing much of a change. How do you motivate yourself to continue to workout ... get up, get going, etc?

TIA!