But that study focused on robust, young adults and repeated, if diminutive, workouts sprinkled throughout the day. The scientists now wondered if a more practical, single session of four-second sprints would be enough exercise to improve health and fitness in out-of-shape adults well past their college years.
So, they recruited 39 of them, men and women aged 50 to 68 who were sedentary but had no other major health concerns. They tested the volunteers’ current aerobic fitness, muscular power and mass, arterial flexibility, and ability to perform what are called “activities of daily living,” such as getting up out of a chair.
The volunteers began visiting the performance lab three times a week. There, they completed a brief workout of repeated four-second intervals on the lab’s specialized bikes. At first, they sprinted for four seconds, with Dr. Allen calling out a second-by-second countdown, followed by 56 seconds of rest, repeating that sequence 15 times, for a total of 60 seconds of intervals.
Over two months, though, the riders’ rest periods declined to 26 seconds and they increased their total number of sprints to 30 per session.
At the end of eight weeks, the scientists retested everyone and found substantial differences. On average, riders had increased their fitness by about 10 percent, gained considerable muscle mass and strength in their legs, reduced the stiffness of their arteries and outperformed their previous selves in activities of daily living, all from about three to six minutes a week of actual exercise.
A majority of the volunteers also told the researchers during follow-up interviews that they enjoyed the workouts and would continue them, if possible, Dr. Coyle said.
The upshot, he said, is that these intervals, despite being as brief as possible, effectively boosted health and fitness in ordinary adults.