Hello there!

I have a small problem with understanding equations from the article that I am making presentation of. If there was a person, who would like to explain me them, I would be grateful.

Link for the article (from Journal of Biomechanics):

https://ibb.co/mb1xYF
I understand that the athlete is interacting with the pole and that's what the first 5 equations are talking about (both forces and moments), but a problem appears later. The symbols used are not described in this paper. Help