Translation:It is tiring to run a lot.
Let's be real though, with the amount of "unnatural" translations Duo has (and often enough outright encourages), especially here, I think it would be par for the course. (Pun not intended.) Perhaps rather literary or formal than everyday, but I'd argue it's quite natural, certainly more so than many other examples I've come across in this Japanese course.
The question is "The tips explanation before the lessons uses のが This lesson uses のは So I assume either can be used to nominalize depending on context of subject or topic of sentence ?" It is not rendered correctly here.
Yes. の is to make a whole clause into a noun. So it can be followed by all the possible particles that can be added to a proper noun. e.g. のは、のが、ので、のに、のも、のを