FROM THE GYMS of pro bodybuilders to the training room of Olympic marathoner Galen Rupp to Mark Wahlberg’s 4 a.m. Club, there’s one unique training tool in common. Maybe you’ve seen people wrap their muscles tight with straps and cuffs, cutting down blood supply to their extremities, then pumping through biceps curls, leg extensions, and even split squats. Blood flow restriction training (or BFR) is breaking out beyond the realm of the PT office and internet forums, thanks to the trend-hopping nature of fitness culture and newer, more affordable consumer devices that have hit the market over the past few years.
The idea behind blood flow restriction is right in its name: Strap a band or cuff above a target muscle, and the amount of blood that can reach and leave the muscle during exercise is restricted. This creates an artificial version of the pump you’d get at the end of a long set, and can—when used correctly—facilitate muscle growth with lighter loads that you’d normally need heavy weight to achieve.
“So if you use those same lighter loads without BFR, then BFR is superior [for creating muscle growth],” says Shawn Arent, Ph.D., C.S.C.S., chair of the Department of Exercise Science at the University of South Carolina. Arent has studied BFR in his laboratory, applying it to a minimal equipment regimen designed for military personnel in the field. But, he adds, BFR protocols alone usually can’t outperform heavier weights, and don’t provide the same strength gains as more massive loads.
Arent isn’t alone in putting BFR to the lab test. Over the past few years, scientists have released a new study—or two, or 10—on BFR training seemingly every month. And they’re finding new benefits and use cases for the practice: BFR is being used for active recovery and to enhance endurance performance along with the more traditional muscle-pumping applications.
Here’s the latest on BFR, the benefits and drawbacks of giving your muscles the big squeeze, and how you can try it safely.
How—and Why—Restricting Blood Flow Builds Muscle
The concept of BFR has been around for almost 100 years, when doctors used the technique to help regenerate tissue in patients experiencing problems with lower-body circulation. Until recently, it was mostly used in rehabilitation contexts.
“You may have someone who is limited in the loads that they can handle due to injury or recovery,” Arent says. For example, in ACL rehab, when the knee can’t handle heavy loads, BFR can be used to train and strengthen the quadriceps. When Arent himself was recovering from having discs replaced in his neck, he used BFR to train. “I wasn’t allowed to train with heavy loads, but I was still able to… maintain strength and mass until I could train heavier again.”
Training with light weights to failure will help to build muscle, says Nicholas Rolnick PT, DPT, MS, CSCS, founder of The BFR Pros. But he notes that BFR allows you to reach failure while using those lighter weights in fewer reps. This means that when using BFR to strength train with blood flow properly restricted, guys can gain muscle while using weights that are just 30 percent of their one-rep maximum … about half the amount you’d use for “normal” strength training.
Still, BFR remained mostly confined to rehab situations, at first because measuring how much blood was being restricted required large, lab-sized equipment that needed to be attached to a wall, then as more portable solutions were developed, they were expensive. Bodybuilders and other DIYers would use straps or surgical tubing to enhance their pump, but doing so didn’t always provide enough blood restriction—or it provided too much, putting guys at risk for nerve and vascular damage. A breakthrough came when Yoshiaki Sato, Ph.D., M.D., a Japanese weightlifter, developed a system with pneumatic bands and digital controls, which paved the way for the consumer-level cuffs available today. These recent smart solutions, which often come with either connected apps or purpose-built digital controls, have cut the cost from the days of medical-grade devices from the thousands of dollars down to the hundreds—and remove the guesswork of DIY operations. That increased accessibility is helping scientists better understand how and why BFR builds beef.
The mechanics of BFR essentially work like this: by impeding blood flow, oxygen-poor blood gets “trapped” in the muscle. The veins are partially blocked, so the blood can’t get out, and the arteries are blocked, so fresh, oxygen-rich blood can’t get in. Veins carry deoxygenated blood from the tissue to the heart. When the veins are blocked, old blood cannot escape, and new, oxygenated blood brought in by the arteries stagnates and creates pressure. Muscle cells become engorged with blood, creating that instant pump. Lactic acid pools in the muscles and your body thinks it’s under extreme duress. (That means if you’re properly doing BFR on your legs, you’re going to get a response in the muscle tissue of your arms as well.)
Being in this oxygen-poor state also causes lactate to build up in the muscle, which can trigger muscle-building hormones like IGF-1 and HGH. The swelling of the cells, the same type of swelling experienced during a pump, may also contribute to long-term muscle growth, Arent says.
Scientists still aren’t sure of all the mechanisms that cause BFR to work for muscle gain. Metabolites, which are byproducts of muscular strain like lactate, may contribute to BFR-related gains, but researchers aren’t sure which of them do what, according to Arent. Experts agree (and research suggests) that there’s still much to learn, including what’s truly causing the hypertrophy during BFR. We don’t know, for example, whether the pressure on the muscle itself may cause more of the hypertrophy than the oxygen-poor state. Arent also points out that since most studies on BFR are done for short periods and with people who are new to this kind of training, it’s not clear whether the benefits continue in the long term—or if there’s a kind of “BFR noob gains” going on.
And while BFR might have a legacy of DIY practitioners using trial and error to find the right balance, the modern version of the practice won’t put you at risk, as extreme as the name implies the practice to be.
“I think the name makes it sound a lot worse than it is, to be honest,” Arent says. Concerns have been raised over the years that restricting blood flow could cause clots or actually damage the muscle, but when done at appropriate levels, research has shown BFR to be safe. “You don’t want to fully occlude the artery, for example. You need to be somewhat smart about this, and not think, ‘well, the more it sucks, the better it is.’”
The New Benefits of BFR
BFR can improve aerobic performance in cardio work, Rolnick says, by improving the quality and number of mitochondria in our muscles. When our muscles are strained by BFR during lower-intensity cardio, the body responds by creating more of these organelles, which are responsible for creating our muscles’ primary fuel source, adenosine triphosphate, or ATP. More mitochondria means more oxygen can be delivered to the muscles during aerobic exercise, meaning more endurance.
Athletes also use BFR when they aren’t exercising to help speed recovery. Instead of impeding their performance with blood flow restriction, they’ll use it “passively” on off days, with their cuffs applying pressure for three to five bouts of three to five minutes at nearly 100 percent occlusion while they’re just sitting.
“There’s evidence coming out now showing that doing BFR passively either before or after a damaging bout of exercise can actually mitigate exercise-induced muscle damage and get you back to exercise faster,” he says. This encourages fresh blood to flow through the muscle, clearing out metabolites that can result from muscle damage and slow down recovery.
How to Get Started with BFR Safely
The first thing to know about BFR and your training is that you don’t have to do it to make gains.
“I’m the BFR guy that says for people not to do BFR,” Rolnick says. If you’re healthy enough to lift heavy weights, he says, “heavy lifting is going to confer the greatest musculoskeletal benefits. We’re going to get the best long-term muscle growth. We’re going to get the best adaptations for our tendons, improving their stiffness and their ability to transmit load to the bone.”
To figure out how much pain is safe to make gains, Rolnick suggests trying an acclimation session with a trainer who is experienced in BFR. There aren’t many personal trainer certifications for BFR yet, but some companies—including B Strong, the manufacturer of the cuffs Arent has used in studies, and Rolnick’s BFR Pros organization—do offer training courses for fitness professionals, so you can ask if your trainer has taken one. Rolnick recommends looking for trainers using cuffs that can dial in a pressure versus guessing at how much blood is being restricted.
BFR, he says, can make your muscles grow with lighter weights, but it usually doesn’t work as well as heavy lifting would. Your workout will also take more time than heavy lifting, since you’ve usually got to do more reps—15 or more—than the number you’d do with heavier weight. The cuffs can also be expensive, with the most effective single-chamber cuffs denting your wallet at $300 (or more). Arent points out another downside of regular BFR use: It hurts. Cutting the blood flow off to your muscles is really uncomfortable.
Still not scared off? In a paper he co-authored for the National Strength and Conditioning Association, Rolnick suggested two ways to incorporate BFR into workout sessions: as a finisher for isolation exercises (hitting a high number of reps), and for deload weeks.
You can also use these three approaches:
For Light Training
Once a week, ditch heavy weights. Pick three strength exercises. Start with a set of 30 reps for each motion, then do 3 sets of 15 reps each. Rest 30 seconds between sets.
For Recovery
Lie down with cuffs tightly wrapped on your upper thighs and fully occlude blood flow for five minutes. Allow normal blood flow for five minutes; repeat three times.
For Finishing Off Your Workout
Do four sets of a heavy bench press at the end of a workout, sans cuffs. Then grab light weights, attach the BFR cuffs, and do an isolated triceps move. Do 30 reps the first set, the 15 reps for the other three sets.
No matter how you choose to employ BFR, Arent says, it’s important to remember that it’s a supplement to normal training. That’s the way the pros use it: as a protocol that allows them to do more than they normally could. With that in mind, keep your BFR sessions to 1 to 2 per week.
Greg Presto is a fitness and sports reporter and videographer in Washington, DC.
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