Similarly, a broader, longer-term study involving out-of-shape, older adults showed that regular, four-second interval workouts, during which volunteers repeated the tiny but intense intervals on the bikes at least 15 times per session, significantly raised their aerobic fitness and leg muscle mass after eight weeks.
But whether four-second interval workouts meaningfully would improve fitness and muscular power in people who started off in good shape was not yet clear. So, for the new study, which was published in July in Medicine & Science in Sports & Exercise, Dr. Coyle and his colleagues persuaded 11 healthy, active young men and women to come to the lab and push themselves through 30 repetitions of the four-second, all-out efforts on the bikes, with at least 15 seconds of rest in between. The volunteers completed three sessions of these intervals each week for eight weeks, for a total of 48 minutes of exercise over the two months. They did not otherwise exercise during this time.
In that time, they added 13 percent to a crucial aerobic fitness measure and 17 percent to their muscular power, measured by how many watts they produced while pedaling the bike, the researchers found.
These results suggest that a few seconds of strenuous effort “definitely provide enough stimulus” to bolster already-robust hearts and muscles, Dr. Coyle said. In practice, he continued, this might mean repeatedly sprinting uphill for four seconds at a time or taking stairs two or three at a time in four-second spurts.
The study’s implications also are cautionary, though, he pointed out. Other research, including his earlier study with students, suggests that being sedentary for long periods could have damaging effects on metabolic health, undermining the benefits from high-intensity workouts. So, if you rip through multiple four-second intervals in the morning and then sit, almost unmoving, for the remaining seconds of your day, you may wind up with metabolic problems related to being sedentary, despite those earlier four-second spurts of motion.
“In general, it’s going to be a good idea to get up and move around throughout the day,” he said, “and then sometimes, also, to move around in a way that is physically intense,” even if it lasts as little as four seconds.