Every four years, the Summer Olympics shows the world the latest training or recovery method the greatest athletes have taken up

This year, the hot thing appears to be tourniquets. No, there is no outbreak of cuts. But the American swimmer Michael Andrew is wearing tourniquet-like bands in the practice pool. Galen Rupp, the defending bronze medalist in the marathon, sometimes straps similar bands to his legs while training. They are among the elite athletes who have become disciples of a practice known as blood flow restriction, which is exactly what it sounds like: cutting off blood flow to certain muscles for limited periods to both enhance the effects of training and stimulate recovery.

The practice has come into vogue in time for the Tokyo Games, and a Japanese former power lifter named Yoshiaki Sato, who developed it in 1966, is finally having his moment. Sato thought perhaps there might be some connection between cutting off blood flow to muscles and training them. He began tying karate belts and later bicycle inner tubes around his legs and performed a series of experiments, tracking how much the circumference of his thighs and calves would grow even when he performed fewer repetitions.

“It was always just a matter of time,” he said this month in an interview from his home in Fuchu, a suburb of Tokyo. “I just did not think it would take this long.”

In recent years, blood flow restriction gained an important advocate across the Pacific in Dr. Jim Stray-Gundersen, a physician and sports medicine researcher who has worked closely with Olympic organizations in the United States and in Norway

“You can get the benefits of swimming 10,000 yards by swimming maybe a thousand,” he said recently.

Andrew, 22, a rising star who will swim three individual events and participate in relays in Tokyo, said he first started experimenting with blood flow restriction five years ago at the urging of Chris Morgan, a veteran swim coach. He often straps the bands onto his arms for 25-yard sprints and tries to achieve the same times as when he is not wearing them. “But you are simulating a sensation of real pain that tricks the body into regrowth.”

Before and after training and races, Andrew straps a gadget high onto each leg, then increases and decreases the tension of the tourniquet at regular intervals — think of a blood pressure cuff — to stimulate blood flow and recovery. Sometimes he wears the bands in the ready room before heading out to the pool deck for a race.

Like any good sports scientist, Stray-Gundersen wanted to see the data when a colleague told him that blood flow restriction was helping his athletes build muscle mass in two weeks that normally took six. As it turned out, there was a paper from 2000, published by Sato and scientists at research institutes in Japan, in the Journal of Applied Physiology. Put simply, the paper argued, blood flow restriction prompted an outsize response from the brain to speed up the normal process of repairing and rebuilding damaged tissue. Cutting off blood flow, then switching it back, can spur the brain to use more healing powers than it would normally think it needs.

Since that study, a number of independent researchers have confirmed the potential benefits of restricting blood flow during exercise. Shawn M. Arent, the chairman of the Department of Exercise Science at the University of South Carolina, is currently conducting a study on its effects for the Defense Department.

For someone like Andrew, who swims thousands of yards every day, or Rupp, whose regimen includes more than 100 miles each week plus weight training and core work, or Noah Syndergaard, the pitcher for the Mets, or Mikaela Shiffrin, the champion skier, or any of the other top athletes who have started incorporating blood flow restriction, the technique allows them to reduce the likelihood of a repetitive stress injury and speed up recovery time.

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