The exercising volunteers gathered during the workweek at the lab for strength testing and weight lifting, of a kind. They sat at a machine called an isokinetic dynamometer, which has a long lever arm that can be pushed and pulled, up or down, with varying levels of resistance, allowing researchers to precisely control people’s movements and effort.

The volunteers manipulated the weighted lever with all their strength, straining and contracting their biceps to the fullest possible extent. Some of the participants slowly lifted the lever’s weight, like curling a dumbbell, producing what is called a concentric contraction, meaning the biceps shortened as they worked. Other volunteers slowly lowered the lever, creating a so-called eccentric contraction. You get an eccentric contraction when you lengthen a muscle, like lowering a dumbbell during a curl, and it tends to be more draining. A third group of volunteers held the lever’s weight steady in midair, fighting gravity, in a type of contraction where the muscle doesn’t change length at all.

And each of the participants did their biceps exercise for a total of three seconds.

That was it; that was their entire daily workout. They repeated this exceedingly brief exercise routine once a day, five times a week, for a month, for a grand total of 60 seconds of weight training. They did not otherwise exercise.

At the end of the month, the researchers retested everyone’s arm strength.

Those three-second sessions had changed people’s biceps. The groups either lifting or holding the weights were between 6 and 7 percent stronger. But those doing eccentric contractions, lowering the lever downward as you might ease a dumbbell away from your shoulder, showed substantially greater gains. Their biceps muscles were nearly 12 percent stronger overall.

These improvements may sound slight, but they would be biologically meaningful, especially for people new to weight training, said Ken Nosaka, a professor of exercise and sports science at Edith Cowan University in Joondalup, Australia, who collaborated on the study. “Many people do not do any resistance training,” and starting with very short workouts may be an effective way for them to begin a strength training regimen, Dr. Nosaka said. “Every muscle contraction counts” and contributes to building strength, assuming you lift a weight near the maximum you can handle and it lasts at least three seconds, he said.