Exercise vigorously for 4 seconds. Repeat. Your muscles can thank you.

Similarly, a broader, longer-term study involving older adults showed that regular four-second interval workouts, where volunteers repeated the tiny but intense intervals on the bike at least 15 times per workout, maintained their aerobic fitness and leg muscle mass eight weeks.

But it was not yet clear whether a four-second interval workout would sensibly improve the fitness and muscle strength of people who started in good shape. For the new study, published in Medicine & Science in Sports & Exercise in July, Dr. Coyle and his colleagues convinced 11 healthy, active young men and women to come to the laboratory and push themselves through 30 repetitions of the four – second, full effort 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 training over the two months. You did not do any other sport during this time.

During this time, they contributed 13 percent to an important aerobic fitness exercise and 17 percent to their muscle strength, measured by how many watts they produced when pedaling the bike, the researchers found.

These results suggest that a few seconds of strenuous exertion “definitely provides enough stimulus” to strengthen already resilient hearts and muscles, said Dr. Coyle. In practice, he continued, this could mean sprinting uphill for four seconds over and over, or taking four-second jumps up two or three flights of stairs at a time.

However, the implications of the study are also cautionary, he stressed. Other research, including his previous study with college students, suggests prolonged range of motion could have detrimental effects on metabolic health and undermine the benefits of high-intensity exercise. So, if you go through several four-second intervals in the morning and then sit almost motionless for the remaining seconds of your day, you can end up with sedentary-related metabolic problems despite those earlier four-second bursts of movement.

“In general, it is a good idea to get up and move around all day,” he said, “and then sometimes exercise vigorously,” even if it takes as little as four seconds.

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