[cameldrv]

I think the definition of vigorous is roughly 75% of max heart rate. HIIT would generally be more strenuous than that. Roughly speaking for a lot of people, running faster than about a 10:00/mi pace is probably vigorous.

In the WHO recommendations, they say to get 75 minutes of vigorous or 150 of moderate per week. I believe in this study they use the same double counting of vigorous minutes.

I’ve seen other studies that say you get most all of the cardio benefit you can with about 150m vigorous/300m moderate. You could roughly get that by running about 2.5 miles per day.