Can 4 seconds of exercise make a difference?

In what is probably the definitive word on how little exercise we can get away with, a new study finds that a mere four seconds of intense intervals, repeated until they amount to about a minute of total exertion, lead to rapid and meaningful improvements in strength, fitness and general physical performance among middle-aged and older adults.

The study relied on a type of specialized stationary bicycle that is not widely available, but, even so, the results suggest that strenuous but super-abbreviated workouts can produce outsize benefits for our health and well-being, a timely message as we plan our New Year’s exercise resolutions.

High-intensity interval training, or HIIT, is an approach to exercise that consists of quick spurts of draining physical effort, followed by rest, with the sequence repeated multiple times. In studies, short

HIIT workouts typically produce health gains that are equal to or more pronounced than much longer, gentler workouts.

But the ideal length of the intervals in these workouts has been unsettled. Researchers studying HIIT agree that the optimal interval span should stress our muscles and other bodily systems enough to jump-start potent physiological changes but not so much that we groan, give up and decline to try that workout ever again. In practice, those dueling goals have led HIIT scientists to study intervals ranging from a protracted four minutes to a quickie 20 seconds.

But Ed Coyle, an exercise physiologist at the University of Texas in Austin, and his graduate assistant Jakob Allen suspected that even 20-second spurts, performed intensely, might exceed some exercisers’ tolerance. So he decided to start looking for the shortest possible interval that was still effective.

And in the new study, published in Medicine & Science in Sports & Exercise, he and his colleagues settled on a four seconds.

Of course, most of us do not have access to the kind of specialized stationary bicycles used in this study. To reach similar, all-out efforts in more typical workouts, Coyle said, we might need to sprint up a hill or staircase as hard as possible or run and jump in place vigorously or furiously pedal our spin bike.

In these situations, the time needed to achieve all-out effort is likely to be more than four seconds, he said. But even if the time commitment is doubled, most of us probably could resolve to exercise in 2021 often and intensely for eight seconds at a time.