People starting out aren’t told often enough that’s it’s perfectly OK to do the run/walk thing, where you might alternate running and walking for a few minutes at a time over the course of a half hour.

Sorry (actually, I’m not really sorry) you can’t be so dismissive. The 20% study you’re referring to is probably the research done by Dr. Jamie Timmons. But what his research has been pretty grossly overstated in various articles, as is typical in most health reporting.