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.

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The study relied on a type of specialised stationary bicycle that is not widely available, but, even so, the results suggest that strenuous but super-abbreviated workouts can produce benefits for our health and well-being.

I have often written about the potential benefits of brief, high-intensity interval training, or HIIT, 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 duelling 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, which was published in Medicine & Science in Sports & Exercise, he and his colleagues settled on a blink-swift four seconds.

They arrived at that number by first working with competitive athletes at the university’s human performance lab. Muscular and fit, the athletes generated enormous speed and power on specialised stationary bicycles that feature a heavy flywheel and no resistance. During fitness testing on these bikes, most of the athletes would reach their maximum power output and all-out aerobic effort after about two seconds of hard pedaling. (Coyle has equity in the company that manufactures the bicycles, but says this monetary involvement does not affect research results from his lab.)