Answer:

The answer probably depends on your capacity for suffering, according to scientists who study high-intensity interval training, which is designed to briefly strain your body to its limits. Studies show that these short bursts of very intense exercise lead to beneficial physiological changes similar to those achieved after much longer moderate workouts. But precisely how much or little intense exercise is best remains in question.

When Martin Gibala, a professor of kinesiology at McMaster University in Canada and an expert on intervals first began studying their effects, he asked young male volunteers to grunt through all-out 30-second intervals performed at 100 percent of the men’s aerobic capacity. The volunteers became much more fit after a few minutes a week of such strenuous interval training, but they also generally hated the process, Dr. Gibala said.

So he and his colleagues developed a less taxing 60-second interval program that requires the hard exercise be performed at only about 90 percent of a volunteer’s maximum aerobic capacity. The drawback was that the men had to do more of these one-minute intervals to gain the same fitness benefits as from the 30-second variety.

Recently, Dr. Gibala and other researchers have been experimenting with intervals as short as 20 seconds performed all-out, as hard as someone possibly can stand, followed by a recovery period of two minutes between each interval. The thinking, Dr. Gibala said, is that these 20-second intervals, although grueling, are more tolerable than 30 seconds of the same exercise and more potent than gentler 60-second intervals. The results so far are encouraging, he said, with volunteers gaining fitness and improving their health after only a few of the 20-second intervals per week.

Or for those, like me, who find even 20 seconds of absolutely all-out physical effort daunting, researchers in Denmark have concocted a high-intensity interval training workout that requires only 10-second bursts of burning, painful effort, preceded by 30 seconds of gentle exercise and 20 seconds of moderate effort. I like this workout.

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P.S.  I perform my intervals at about 85% to  90%  of my maximal heart rate for a minute and rest at 65% for two minutes. I do seven intervals which lasts for 23 minutes. I take 1  minute to warm-up and 1 minute to cool down for a total of about 25 minutes for cardio three days per week. Ideally – with hiit weigh training this can be cut in half.

P.P.S. Visit exercises for diabetes for more information on getting the most for out of a proper workout program.