IMV Doesn't matter, they are separate things. You can do both as you want but don't forget the 50% rule. You need to be doing your own thing and not just studying.

I would caution that from what I know both drawabox and Proko anatomy are rather heavy courses. Proko especially is very detailed. Doing them both at the same time could be very tedious and make you a bit tight and over-analytical in your drawing. A key thing with figure drawing is to understand gesture drawing as someone else has said. It really is the basis for it.

Aaron Blaise does a human anatomy course that might be a better introduction. Michael Hampton has a figure drawing book that is consistently recommended by many artists. He has a youtube channel but it is supporting material for the book rather than a course.