The takeaway of both studies is that it is best, if you wish to perform high-intensity interval training, to stick to what is well documented as effective: a few sessions per week of 30- or 60-second intervals so strenuous you moan, followed by a minute or so of blessed recovery, and a painful repetition or four. Done correctly, such sessions, in my experience, get you out of the gym quickly and inspire truly inventive cursing.