They’re popular and they’re quick. Actually, they’re popular because they’re quick, but high intensity workouts are not all equally beneficial. Gretchen Reynolds reports in the New York Times on research conducted at McMaster University that compared the benefits a single daily high intensity bout to those of repeated intervals of high intensity training. Reynold reports that researchers at the school divided 17 healthy young men and women into groups. Ten were asked to exercise on two separate days so that on one day they completed a standard HIIT session consisting of four 30-second bouts of all-out exertion, alternating with four minutes of recovery between. On another day they completed a single interval lasting for about four minutes, but one that used the same amount of energy as during the stop-and-go session. Another seven volunteers did the continuous four-minute workout three times a week for six weeks.
After six weeks, Reynolds writes, blood and muscle samples showed no variations in how the muscles of riders in the first group responded to a single session of interval training, whether of the standard stop-and-go variety or a sole sustained effort. All participants had augmented amounts of chemicals that help muscles produce energy. But wait, when the researchers studied the blood and muscle of the second group of riders after they had completed six weeks of single-interval training, they found that their muscle tissues now had only average — not augmented — amounts of the chemicals that help cells to produce more energy, which Reynolds calls “a marker of fitness.” The bottom line? “There is something important, even essential,” one researcher says, “about the pulsative nature of on-off HIIT training if you wish to reap sustained physiological improvements.” Read more in the New York Times.