Physical therapist Johnny Owens is widely recognized as a leader in the wider adoption of BFR in the United States. He worked for the Department of Defense from 2004 to 2015, where he was director of human performance optimization at Center for the Intrepid, a rehabilitation center for veterans with severe combat wounds. There, Owens began implementing BFR training with patients recovering from severe musculoskeletal trauma. The method’s dramatic results, with people seeing anywhere from 30% to 300% strength gains within just two to four weeks, led professional sports teams to adopt BFR, and eventually other orthopedic rehabilitation practitioners followed suit. Through his company, Owens Recovery Science, Owens says he has trained more than 3,500 practitioners in BFR.

“When I first started hearing about it, it sounded crazy,” says physical therapist Heather Milligan. “Why would I take a professional athlete or patient who just had surgery and put a tourniquet on them?” But four years ago, she took a BFR course and became a convert. Milligan says she now uses BFR with all sorts of patients, from competitive athletes to senior citizens. It also has the potential to achieve results previously thought impossible with the most stubborn injuries. She points to the example of an Achilles tendon rupture, a severe or complete tear of the tendon that attaches the calf muscle to the heel. “That injury is notorious, because it leads to tons of muscle atrophy in the calf. But if we can apply tourniquet training, we see minimal to no atrophy,”she says. “That is unheard-of.”

When the flow of blood, and therefore oxygen, to a muscle is restricted, even simple exercises become very difficult. “What we’re doing is creating an environment where your body is perceiving that it’s doing a lot more work than it actually is,” Milligan says. “You’re creating a metabolic overload instead of a mechanical overload. In that metabolic state, where you’ve burned out all the oxygen, that begins a physiological hormone cascade that generates more muscle and increases blood flow to area.”

Though research into BFR’s exact mechanisms is ongoing, current literature shows that BFR increases electrical activity within muscle tissue and produces increases in growth hormone and cortisol comparable to those seen after intense weightlifting. Bowman and Milligan worked on one of the first randomized controlled trials of BFR. Their results for lower-extremity exercises have been published, and results for an upper-extremity trial are forthcoming. Their study included a control group that performed the same exercises without BFR. Even within the BFR group, patients used tourniquet training only on one side so researchers could compare the BFR limb and the non-BFR limb within the same person. They found that BFR increased strength in muscles both proximal and distal to the tourniquet. Within the BFR group, even the non-BFR limb saw some benefits, suggesting that BFR leads to a systemic response that could affect the whole body, not just the limb where the tourniquet is applied.

Though BFR research has been underway for decades, many of these studies have been very small. Experts agree that larger, higher-quality studies are needed to determine safe and effective treatment protocols for a wide variety of patients and conditions. “There is a dramatic increase in quality studies currently underway,” Bowman says, many examining use of BFR in rehabilitation for common sports injuries like ACL tears and rotator cuff (shoulder) injuries.

“We know that athletes and service members respond super well,” says Owens. “We know the elderly population responds super well.”

People with a history of deep vein thrombosis or blood clotting disorders are still advised to avoid BFR, though most people need not be concerned that BFR will cause blood clots.

Before you run out and strap on an elastic tourniquet for your gym session, experts caution that people should get guidance from a professional. Tying a tourniquet too tight for too long, for example, can cause permanent nerve damage. But BFR with the assistance of a professional is likely to continue growing in use among rehab programs. “Though I don’t expect BFR to be able to answer every rehabilitation challenge possible, it is without doubt a very important innovation that has changed the approach to rehabilitation on a worldwide scale,” Hughes says.