Why kaatsu, a fitness trend spotted at the Games, isn't just for Olympians

Pictured are current Olympians Galen Rupp (left) and Michael Andrew (right), and past Olympian Mikaela Shiffrin (middle).

(CNN)Restricting your blood flow sounds like a dangerous thing to do, but it's exactly what some Olympians, athletes, and surgery and physical therapy patients have done to strengthen their muscles and speed up recovery.

The origins of this practice go back to 1966, when -- while sitting on his heels during a Japanese temple ceremony -- Yoshiaki Sato noticed his calves felt tingly and pumped up. Sato wondered if his limited blood flow was the key to experiencing that sensation, said Steven Munatones, the CEO of KAATSU, an eponymous blood flow restriction product and education company. Munatones cofounded KAATSU Global -- which translates to "additional pressure" in English -- with Sato in 2014 after being mentored by him about the Kaatsu technique for 13 years in Japan.
Seven years after that initial tingly feeling, Sato "experimented with different kinds of bands placed on different locations on his body -- from his head to his torso to his lower legs," Munatones said via email. "In 1973, he experienced a broken ankle and rehabilitated himself using KAATSU."
    This was the first experimentation with KAATSU cycle mode, Munatones added, which is when bands with internal "air bladders" are inflated for 30 seconds as the bands compress around upper limbs, then deflate for five seconds before repeating the cycle. This rhythmic compression slows the blood flow back to the heart and therefore allows the veins and capillaries in the treated areas to engorge with blood -- visible as the skin gradually reddens -- while you're exercising, Munatones said.
      This engorgement expedites several naturally occurring biochemical reactions, such as secreting nitric oxide, human growth hormone, insulin growth factor-1 and beta endorphins, all of which have differential roles in increasing blood supply, preventing tissue damage, regulating body composition and muscle growth, growing bone and tissue, and suppressing pain.
      "Individuals exercise during the application of BFR to improve muscle mass, muscle strength, reduce pain, improve recovery, increase cardiovascular capacity and augment sports performance," said physical therapist Nicholas Rolnick via email.
      Since Sato's discovery and subsequent studies on thousands of people, athletes, fitness enthusiasts and Olympians -- including long-distance runner Galen Rupp, diver Laura Wilkinson, swimmer Michael Andrew and alpine skier Mikaela Shiffrin -- have benefited from the technique. But you don't have to be an athlete to use Kaatsu or blood flow restriction training -- here's what experts say you should know before you try it.

        How it works

        When someone exercises while practicing Kaatsu or blood flow restriction, blood and metabolic byproducts are "stuck in the muscle, unable to leave," Rolnick said.
        "The metabolites increase muscle fatigue, causing the muscle to work much harder than it normally would to produce a contraction at light loads," he added. "We have to work very hard to keep up with the exercise and that extra effort, paired with the fatigue produced through the BFR, accelerates muscle mass and strength gains."
        Muscle fibers required to perform high-intensity actions -- such as jumping, throwing, lifting weights or kicking -- are recruited at lower intensities than usually required, said Stephen Patterson, a professor in applied exercise physiology and performance at St Mary's University, London, via email. That means someone could lift 20% to 30% of their maximum weight instead of the usual 70% or greater, and still experience a response like that of training with heavier loads, he added.

        Need-to-knows before attempting BFR

        People these experts have sold related products to, treated or studied include athletes of nearly all levels of ability, people who lead sedentary lifestyles, and those recovering from injuries, and range from 18 years old to 104.