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.
Martin Gibala, the chairman of the department of kinesiology at McMaster University and senior author of the study, but "it would appear," he said, "that there is something important, even essential, about the pulsative nature" of on-off HIIT training if you wish to reap sustained physiological improvements.
The results of the other major new study of interval training, this one published this month in PLOS One and undertaken at the Norwegian University of Science and Technology in Trondheim, Norway. In it, scientists asked volunteers to perform a total of 24 standard HIIT sessions over either three or eight weeks, meaning that the volunteers exercised either three times per week or almost every day and sometimes twice on the same day.
At the end of the prescribed time, those who had completed three HIIT sessions per week had improved their endurance capacity by almost 11 percent. But those exercising daily displayed no such improvements and, in some, endurance declined