If you've never used them, you might be wondering: what do Kaatsu and similar BFR bands feel like? "Just like a blood pressure cuff," says Jamie Burr, a cardiovascular and exercise physiologist at the University of Guelph in Ontario, Canada. "You can feel the congestion of blood. There's a tightness and a pressure."
When blood flow is restricted to active muscles, your body can't effectively clear lactic acid, which leads to a buildup of metabolic byproducts that bathe your muscle fibers in a stress-inducing mixture. "In my lab, we affectionately refer to that as marinating," says Burr.
Once blood is allowed back into the marinated muscles, your body will work extra hard to repair them, stimulating growth and strengthening. Essentially, this mimics the effects of very intense exercise using a much lower workload. A systematic review of 237 studies on BFR training found that 78 percent reported "significant" increase in muscle strength compared to a control group.
Aside from elite athlete training, BFR could be beneficial as a therapeutic tool. To test this application, Burr and his team are conducting a study in which healthy athletes use a cast and crutches on one leg to simulate muscular atrophy after a broken bone. After two weeks, the researchers divide the participants into four groups: one treated with BFR, one with electrical stimulation, one with a combination of BFR and electrical stimulation, and one that received no treatment.
The results are yet to be published, but Burr says that they have been encouraging. "Long story short, what we found was this is really effective for an injured athlete in preventing muscle wasting in the first place."