[pwr22]

It's not a symmetric exercise, look at the feet. You'd probably want to keep the overall workout balanced by alternating periodically?

[volemo]

I.e. “don’t skip the left day!”

[scotty79]

It's because walls are a bit too steep. If you made them into paraboloid, a per would naturally climb as high as they need to, to be able to run symmetrically.

[ordu]

But one leg will still be running a shorter distance then the other.