But in that case, we are not exercising for at least four days of the week, which can be problematic. “There are a number of health benefits,” most of them related to better blood sugar and blood pressure levels, he said, that occur only on days when we exercise. When we skip working out, even if we did HIIT the day before, our blood sugar and blood pressure control may slip, undercutting the long-term metabolic gains from those earlier intervals. So, if you decide to do HIIT, plan to schedule other types of exercise, he said, such as moderate walking, cycling, swimming, jogging or calisthenics on most other days of the week.
IT rather than HIIT?
Perhaps the biggest impediment to HIIT for many people, though, is that name.
“I wish we would start using the more-encompassing term ‘interval training,’” rather than HIIT, Dr. Gibala said. “So many people are intimidated, because they think HIIT has to be this all-out, hard-as-you-can-go, gut-busting workout.” It does not, he said. On a green-yellow-red spectrum of physical effort, he said, it is “yellow.”
“You should be able to have short conversations with another person” during a typical interval, Dr. Wisloff said. “But if that person asks you to sing, you should not be able to.”
In practice, this level of effort could mean walking up a hill instead of on level ground, Dr. Wisloff said. Interval walking, in fact, can be an ideal introduction to this kind of exercise. In a large-scale experiment a few years ago in Japan, almost 700 middle-aged and older adults walked for 30 minutes, some at their usual pace, while others alternated three minutes of up-tempo walking with three minutes of strolling. At the end of five months, the interval walkers were considerably fitter and stronger than the others. And when the researchers checked back in with the volunteers two years later, 70 percent of the interval walkers were voluntarily continuing with their interval program.
Keep it simple. Consider fartleks.
Interested in trying HIIT now? Good, Dr. Wisloff said. “I would say that everyone should aim for at least one HIIT session per week, for the sake of health,” he said.
Choose whichever variety of HIIT appeals to you. You might try one minute on, one minute off, meaning you push yourself for 60 seconds, rest for 60, and repeat, or the four-minute interval workouts employed often in Dr. Wisloff’s research, with four minutes of strenuous effort followed by four minutes of rest. Other researchers use four-second intervals, and I have tried and enjoyed the 10-20-30 approach, which was pioneered by scientists in Copenhagen, during which you jog or otherwise exercise gently for 30 seconds, ramp up the effort for 20 seconds and then sprint for 10 seconds, before returning to the easy half-minute jog.
But lately, I have settled into frequent fartleks. Swedish for speed play, fartlek workouts involve picking a goal, such as a tree or light pole up ahead, and speeding up until you reach it. No need to check your heart rate or track each interval’s length, in time or distance, said Dr. Wisloff, who also trains with fartlek. Use the natural contours of the landscape to shape your exercise. “This is perfect to do outside the gym,” he said, with little expense or experience needed. Just dash toward the tree until it recedes behind you, pick another landmark ahead, and you’ll be “HIITing” health and fitness goals.