Don't freak out if you see a guy tying off his arms the next time you're at the gym. Science says that's cool now.
Well, sorta. The technique he's using—and an increasing number of bodybuilding bros are trying, too—is known as blood-flow restriction training. And while there are many reasons why using a tourniquet or improvised devices like weightlifting knee wraps or ACE bandages are a less-than-ideal way to go about it, research shows it's an effective way to achieve an impressive number of fitness goals, including rehabilitating injuries, improving endurance, and building monster-ass biceps—all while lifting surprisingly light weight, or none at all.
Blood-flow restriction training started out in a controlled laboratory setting, then spiraled into off-label use. The technique originated in Japan, where it's known as KAATSU. The man who developed the technique is Yoshiaki Sato, who today wields an impressive set of guns for a guy in his late 60s.
But Sato's original goal wasn't to get swole. According to lore (and KAATSU's website), he was trying to heal a broken ankle he'd managed to fuck up on a ski trip. By occluding, or partially blocking off, the return of blood from his legs while performing isometric holds (think: the "squeeze" part of a rep), he reportedly healed the ankle in 6 weeks—and managed to avoid that one-leg-is-way-skinnier-than-the-other thing that happens when you have a limb in a cast. A couple of decades and a few patents later, KAATSU was born.
Today the main intended use for KAATSU, and its non-patent-ized version, blood flow restriction training, is to help people recover from injuries. "The potential implications that blood flow restriction has for rehabilitation is the thing that excites me the most," says Jeremy P. Loenneke, a professor of health and exercise science at the University of Mississippi who has authored several peer-reviewed papers on blood-flow restriction training. "There's some evidence that applying blood flow restriction in the absence of exercise may be useful for helping to maintain muscle size and strength."
Translation: Even without training, the technique could be a helpful way to avoid the muscle wasting one typically experiences when recovering from something like surgery or a broken bone. Several rehabilitation centers in the US are already employing the practice. "I'd say that 90 percent of the times I've used it have been on the physical therapy side," says Zachary Long, director of physical therapy at Carolina Sports Clinic.
Perhaps you're wondering about that other 10 percent? Of them, Long says, "I work with a lot of strength athletes. Maybe they feel like they have a certain muscle group that's behind and that's limiting their performance."
So let's say one of those athletes wants to build up his biceps. The most commonly prescribed protocol: He blocks off the return of blood from his arms (more below on the ins and outs of how to do this), picks up a set of what are, for him, very light dumbbells (20-30 percent of his max), and starts knocking out high-rep sets of curls. Thirty reps on the first set, followed by three more sets of 15, with about a 30-second rest period between each, keeping the occlusion cuffs on the entire time.
Here's what happens inside muscles when one trains this way: "The trapping of the blood is going to trap lactic acid," Long says. "As you're exercising, you're building up more and more lactic acid…the growth hormone release that occurs in response [to that] is actually higher than what we see with heavy resistance training. One study showed BFR [induced] growth hormone levels were 1.7 times higher than heavy resistance training."
And here's how that feels: "It hurts," says Wilfredo Thomas, a Los Angeles-based trainer and coach who's used blood-flow restriction training for the past six months. "During that first set, you begin to feel an extreme pump." Long agrees: "It should feel like the largest muscle burn you've ever had," he says.
What shouldn't one feel? Numbness or tingling. If that's what a person experiences, it means they've tied themselves off too tightly. While to date, blood flow restriction training has been shown to be generally safe, according to studies published by Loenneke and others, there are some people who shouldn't use the technique: Those with deep-vein thrombosis, varicose veins, high blood pressure, or a history of cardiac disease, for instance. You should also shy away if you've had lymph nodes removed, or if you're pregnant, Loenneke says. And even without those conditions, there are still ways that you could manage to fuck yourself up.
For example, in KAATSU and in rehabilitative settings, you can dial in the specific amount of pressure you're using with compressed air bands, which are kind of like the blood pressure monitor your doctor uses. But these devices are expensive, so many people resort to improvised implements like rubber bands or knee wraps. Which is where things can get ugly.
"If you have a thin cuff, it takes more pressure to restrict that blood flow," Long says. "So if you go on Amazon and search for BFR, you'll see some that are like one inch wide. Those things are freaking horrible. And then people go and they'll put it over their calf or they'll put it around their elbow—places where there are superficial nerves—and that'll lead to problems."
What sort of problems? "Number one is nerve injury," Long says. "Number two, there are a number of cases of skin injuries. If you put too much pressure through the cuffs, you're going to potentially risk damaging skin, damaging arteries and other underlying soft tissues."
So if you do try blood flow restriction training, don't place the cuffs anywhere other than the top of your arms or legs, Loenneke and Long say.
And if you decide not to buy the expensive pressure-monitored cuffs and use something improvised, make it a wider material (something comparable to the 4+ inch wide cuffs your doc uses to take your blood pressure)—and don't use it at anything tighter than what feels like a 7 on a scale of 10. Then do your best to ignore the weird looks from the other people at your gym.
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