Here's what you need to know before you try this technique during your next workout.

By Julia Malacoff
Instagram/@nielsvdknoop

If you've ever seen someone in the gym with bands around their upper arms or legs and thought they looked... well, a little crazy, here's an interesting fact: They were probably practicing blood flow restriction training (BFR), also known as occlusion training. While it might look weird to the uninitiated, it's actually a highly effective method of getting stronger and growing your muscle mass while using weights that are way lighter than what you'd normally need to use to reap the same effects.

But that doesn't mean everyone should be doing it. Here's what you need to know about BFR, including how to tell if it's right for you.

How does blood flow restriction training work?

Blood flow restriction means using a specialized tourniquet system (not unlike what a nurse or similar would wrap around your arm before drawing blood) to decrease blood flow to your limbs, explains Hannah Dove, D.P.T., A.T.C., C.S.C.S., a doctor of physical therapy at Providence Saint John's Health Center's Performance Therapy in Santa Monica, CA. The tourniquet is typically wrapped around the arms just under the shoulder or around the legs just below the hip.

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If you do BFR in a physical therapists office, they will often have a version that looks similar to a blood pressure cuff, which allows the PT to control the level of blood flow restriction.

Why do that? Well, with traditional strength training, you need a heavy load (at least 60 to 70 percent of your one rep max) in order to make your muscles stronger and bigger. With a tourniquet, you're able to achieve the same effect with a much lighter load. (Related: New Study Reveals Yet Another Reason You Should Lift Heavy)

When you lift heavy weights, it creates a localized hypoxic environment in your muscles due to the demand, which just means there's less oxygen than usual. Hypertrophy training uses load (weight) and reps together to reach fatigue and oxygen depletion faster. When that happens, there's a buildup of lactate, which is what causes that "burning" feeling when you're doing a tough workout. Using a tourniquet mimics this hypoxic environment by reducing the blood flow, but without having to actually use heavy weights, says Dove.

"For example, if you would normally have to perform bicep curls with 25-pound weights in order to increase your bicep strength and muscle size, with the use of BFR you would only need to use a one- to 5-pound weight to achieve the same level of strength and hypertrophy (muscle growth)." Research has shown that doing BFR with loads that are 10 to 30 percent of your 1-rep max are sufficient to stimulate muscle growth because BFR simulates the same lower-oxygen environment in your muscles that you'd get by lifting heavier weights.

While this might sound kind of crazy, it's actually not a new idea at all. "Weight-lifters have been tapping into the benefits of BFR for years," says Eric Bowman, M.D., M.P.H., assistant professor of orthopedic surgery and rehabilitation at Vanderbilt University Medical Center in Franklin, TN.

In fact, Dr. Bowman says, a form of BFR called Kaatsu training was created by Dr. Yoshiaki Sato after he noticed significant discomfort in his calves from sitting in traditional posture during a Buddhist ceremony in Japan in the 1960s. He realized this felt similar to the burning sensation he felt while working out and started using bands to replicate the effects. "You may have seen weight-lifters at the gym replicating this by wearing bands on their arms or legs," says Dr. Bowman. Now, BFR is being used all over the world for a variety of purposes.

What are the benefits of blood flow restriction training?

Aside from increased strength (even outside of your BFR sessions) and muscle growth, there are some pretty amazing benefits of blood flow restriction training.

Overall, BFR is a really well-researched method of training. "Most of the published studies have been on small groups of subjects, yet the results are substantial," says Bowman. Since it's been around for many decades in one form or another, there's been a decent amount of investigation into how it works and who should try it. (Related: Common Weight Lifting Questions for Beginners Who Are Ready to Train Heavy)

Here, some example of people who can benefit from blood flow restriction training:

It makes healthy people stronger. In people without injuries, the research-backed benefits include increases in muscle size, strength, and endurance that are similar to high-weight exercise routines, says Dr. Bowman. That means you could lift much lighter weights and still see #gainz.

It also makes injured people stronger. Now, BFR research is being done on people who have recently had operations or who need rehabilitation for one reason or another. A few studies have identified benefits for orthopedic patients, with more currently underway, says Dr. Bowman. "This has the potential to be a major advancement in the way we rehabilitate patients with knee pain, ACL injuries, tendinitis, post-operative knee surgery, and more." BFR is also used in elderly patients who need to get stronger, but can't lift heavy weights. (Related: How I Recovered from Two ACL Tears and Came Back Stronger Than Ever)

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You can do pretty much any exercise with BFR. Essentially, you can take any exercise you do in your usual workout routine, reduce the weight or intensity, add a tourniquet, and get the same results. "You can do anything you normally would do with the BFR: squats, lunges, deadlifts, push-ups, biceps curls, walking on a treadmill," says Kellen Scantlebury D.P.T., C.S.C.S., CEO of Fit Club NY. "The possibilities are really endless."

Sessions are short. "In our clinic, we typically will do one exercise for seven minutes and, at most, will do three exercises total," says Jenna Baynes, a doctor of physical therapy at Hospital for Special Surgery. In other words, you can get a really great workout in a fraction of the time because you're using much lighter loads.

Are there any risks to blood flow restriction training?

But before you run out to buy a BFR strap or a DIY BFR kit, here are a few things you should know.

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You really need to work with a professional to get started. While, with the proper equipment and a properly trained individual, BFR is very safe, says Dove, "you should not try blood flow restriction training without the supervision and guidance of someone who has specific BFR training and is BFR certified. It would not be safe to attempt to reduce the circulation to your own limbs without knowing how to do it correctly or without a way to ensure that the occlusion pressure stays within a safe level," she explains.

The reason for this is pretty simple: There can be severe complications to incorrectly applying and using a tourniquet to your limbs, such as nerve damage, muscle damage, and risk of forming blood clots, says Dove. "As with all forms of exercise, your physician should give you clearance based on your medical conditions and history so that you can get stronger in the safest way possible."

At the moment, in order to perform BFR, you need to be a medical or fitness professional such as a physical therapist, certified athletic trainer, occupational therapist, or a chiropractor who has also passed a blood flow restriction certification class. (Related: How to Make the Most of Your Physical Therapy Sessions)

After practicing with a professional, you may be able to do BFR on your own. In the case of a BFR device that has a pump, Scantlebury says he typically likes to have clients use the device alongside him for at least six sessions before he feels comfortable having them try it on their own. "When using the device for the first time, you need to determine the maximum occlusion levels or the level at which total blood flow is occluded (or blocked) to the extremities." After your maximum is determined, your therapist or trainer will figure out how much pressure the device should have during your training sessions, which will be less than your maximum.

But even if you're just using straps with no pump, it can still be difficult to gauge exactly how tight they should be for the best results, and a certified pro can help you determine that. Ideally, they should be tight enough that blood flow is restricted, but not so tight that you can't move.

It's not appropriate for everyone. "Anyone with a history of blood clots (also known as deep vein thrombosis or pulmonary embolism) should not participate in blood flow restriction training, says Dr. Bowman. Also, those with significant heart disease, hypertension, vascular disease, poor blood flow, or anyone who is pregnant should avoid BFR training as this may increase the risk of stroke.

The Bottom Line

BFR is pretty awesome for increasing muscle strength and size if you know what you're doing and you're being supervised by a pro, but it may not be the best idea to try it out on the first time on your own. If you're interested in trying it, seek out a physical therapist or trainer with a blood flow restriction certification in your area, especially if you're dealing with an injury you think BFR could help you come back from. Otherwise, you can still stick with traditional weight training, because the results are pretty hard to argue with.

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