This is indeed a rather difficult problem just because of all the small differences between people's gaits. A person's height, weight, and activity could all impact a person's gait. I guess that is why it made sense to use a skeletal model. Even though the system has a few outliers, the system does very well considering the difficulty of the problem.

One question I had was that the paper describes that the Martin distance has an advantage over the Finsler distance. What is this advantage?