Blood Flow Restriction Training 101: How BFR Works

When it comes to properly working out, there are certain pieces of advice that are nearly universal, and for good reason.

For example, warming up your body helps to get the blood flowing to your muscles, carrying oxygen and nutrients where they need to be the most.

The same goes for proper breathing throughout a lift—not only does it help control tempo, but you’re also going to be properly oxygenating your muscles. Altogether, this allows for greater power output and greater gains. However, there’s more to the story than just this.

Blood flow restriction training (BFR) is exactly what it sounds like.

By constricting how much blood flows into certain parts of the body, you can get more out of an exercise while using less weight at the same time. Down below we’ll look at the ins and outs of this training technique, and anything you might want to watch out for.

What is Blood Flow Restriction?

First discovered in 1966 by Yoshiaki Sato, BFR was originally called KAATSU (meaning, “added pressure”). Since then, it’s been extensively studied, with more research coming out constantly. While originally slated as a method for rehabilitation, BFR has shown increased interest from those looking to improve their physique with increased muscle growth.

As the name would suggest, BFR relies on wrapping some sort of device (such as a bandage or wrap) around the upper portion of your leg or arm. The point is to restrict the blood flow exiting the limb, meaning that venous flow is restricted. On the other hand, blood is able to enter the muscle through the arterial flow.

This effectively “swells” your muscle with blood, along with other things that are conducive towards muscle growth. It’s important to keep in mind that blood flow isn’t completely restricted, and your muscles are forced to work even harder to pump blood back towards the heart. This also has some interesting effects on the muscular, cellular level.

For example, the restriction of blood leads to lower oxygen levels, increased levels of acidity, and other metabolites that allow for your muscles to get tired more quickly. This means that even if you may not be using a lot of weight, you’re still getting similar benefits with a lighter load.

Part of the reason this is so effective is due to the stress you put on the nervous system. Because your muscles are getting so fatigued and your nervous system can sense it, your body will be using the largest, fast-twitch muscle fibers which will lead to the most impressive growth.

What Happens in the Brain?

But there’s even more that the nervous system does for us when it comes to BFR. Once our brains get the message that we’re not getting enough oxygen, our endocrine system is alerted. This is the system that regulates hormone responses.

In terms of BFR and oxygen reduction, our endocrine system responds by releasing growth hormone—an important hormone for muscle cell growth and reproduction, and fat breakdown. A secondary hormone also gets released, which is important for hypertrophy, bone growth, and the regulation of DNA synthesis. But what does this all mean in terms of practical benefits?

Physical Therapy and Hypertrophy

There have been several studies done on KAATSU training, including meta-analyses. Many of these have been for its rehabilitation usage in developing skeletal muscles. If you’re looking to learn more, many of these studies can be found on PubMed, with Takarada, Abe T.,  and Hughes L. being prolific in this area.

This makes sense when we consider one of the effects that BFR has on muscle development. The lack of oxygen effectively tricks our brains and our bodies into thinking we’re pumping more weight than we actually are. This allows us to put out more reps and train with more volume while lowering the intensity.

When it comes to rehabilitation, lower intensity is important if we’re trying to work around a damaged muscle group or joint. The benefits of lifting weights are unlocked even for those who wouldn’t otherwise be able to use them. Similar benefits can be seen by those who have let their muscles atrophy because of disuse.

Research is increasingly also done on the effects of BFR training for muscle development, or hypertrophy. Much like for the reasons outlined above, BFR can give us a significant increase in development when we’re trying to grow a muscle.

When we consider the lower intensity and ability to go for higher reps, it’s the perfect concoction to squeeze some extra gains out of our work. Studies looking at cross-sectional areas have seen significant increases in size.

The Tools Needed for BFR

Strict, by-the-book BFR is performed using a KAATSU device, which helps to restrict venous blood flow while allowing arterial flow. The greatest benefit of a specialized device like this is that you can more precisely control how much of your blood flow is restricted. Furthermore, it’s also much easier to replicate the same sort of restrictions from workout to workout. However, not everyone is going to have access to a KAATSU.

Other popular options are wraps, tourniquets, and bandages, which serve the same basic function of limiting venous blood flow. However, things like the tourniquet system can be a bit more difficult to work with if you don’t know what you’re doing.

The biggest concern is that you’ll be restricting both types of blood flow—arterial and venous. Since the point of BFR is to bring blood to the muscle and have it stay there (mostly), you want to restrict the veins while allowing arteries to remain relatively unrestricted.

As you can imagine, this can be difficult to properly accomplish for a first-timer. It’s further complicated by the fact that completely restricting blood flow to muscles has also been linked to decreased muscle growth. This can potentially be dangerous as well if both arteries and veins are completely occluded (or, blocked off).

To remedy this issue, it’s a good idea to wrap using a narrower piece of material, whether that’s a bandage or a wrap. Using a narrower wrap significantly reduces the odds of occluding your arteries, while imparting the same benefits with restricting venous flow.

Following this, it’s also a good idea to wrap your bandage over top of itself instead of spiraling down your limb (leading to the restriction of more blood vessels).

Where to Wrap (and How Tight)

There are another two key points to remember when wrapping your restriction tool, whatever it may be.

Along with layering the wraps instead of spiraling, you’ll also want to ensure that you’re wrapping at the top of your legs or arms. Putting the restriction closer to the main joint will help to prevent occlusion from occurring. This location makes sense if you’re training shoulders, chest, or glutes—but even if you’re training calves or forearms, you’ll still want to keep the restriction high up on your limbs.

The other part of wrapping is doing it tightly enough. For one, you want to get the benefits of BFR, so wrapping tight is necessary. But at the same time, you don’t want to occlude both your arteries and your veins. A good rule of thumb is to remember a scale of 10 when deciding how tight it is. “Ten” meaning that you can’t imagine it going any tighter, and 1 being very loose. For BFR to work, and allow enough blood flow, you want to be aiming for 7 on this scale.

The size of your limbs will also dictate how tight you should go. This difference should also be considered when looking at the arms compared to the legs, with arms being at a 6 and legs at a 7. People with smaller or skinnier limbs should consider going a bit looser with the wraps to prevent occlusion from stopping too much blood flow.

If you’re unsure of how tight you should be wrapping, consider that 40% occlusion is just as beneficial as 80% occlusion according to a study done on the subject. Not only does this leave a pretty big window for successful restriction, but it also means that you should be just fine going a bit looser rather than tighter—if unsure. The key is to wrap at moderate pressure and use the correct weights and rep schemes.

How Heavy Should You Lift?

High-volume, low-load routines like BFR usually rely on using high rep counts and lower percentages of your 1 rep max (1 RM). But how low should you go, when it comes to the weights you use?

One important aspect is also to train your fast-twitch muscles, rather than your slow-twitch. That is, after all, one of the key factors of BFR when training for hypertrophy.

Even though research has shown that BFR elicits muscle growth at 20% of one’s 1 RM, these don’t tend to be fast-twitch muscles. Considering this research, it’s best to keep to between 40 and 50 % of your 1 RM when using BFR methods.

The exception to this rule is if you’re using this training for rehabilitative reasons. It’s definitely more important to consider decreasing the load in order to make it easier for your muscles and joints, rather than emphasizing fast-twitch muscle development.

Rest Periods and Recovery Times after BFR Resistance Exercises

High-intensity exercises with heavier weights are known for their long recovery times because of muscle damage and metabolic stress. The heavy weights are extremely hard on your muscles and joints due to the muscle activation, but they do elicit greater muscle strength gains.

On the other hand, low intensity but high-volume training (like you would see in a conventional hypertrophy routine) usually have lower recovery time needs while emphasizing muscle mass development. But how do these methods stack up to BFR training?

A good rule of thumb is to do include BFR into your workout routine every other day, or about 2 to 3 times a week. This will give you plenty of time for recovery, while also giving your muscles enough work to elicit strength and muscle gains.

But BFR does differ from conventional low-intensity workouts by increasing the volume even more than you would see in a standard muscle size emphasizing workout. These extra-high rep counts (which push 30) are very taxing on your body, and if you’re not used to high-rep workouts, you’ll definitely be feeling the burn. This has little to do with the restrictions, however, and more to do with the rep counts themselves.

As with most things, your recovery time will depend on your starting fitness level and comfort level with working out. Anywhere from once to three times a week is a good place to be when it comes to allowing for enough muscle recovery. It’s also a good idea to include some high-load resistance training to optimize muscle protein synthesis. This will have the added benefit of improving muscular strength even more, on top of the development provided by occlusion training.

Staying Safe with BFR

While restricting blood flow seems like a serious thing to do health-wise, sports medicine has shown its safety and effectiveness. However, systematic reviews of sports med also highlight the importance of not completely restricting blood flow with occlusion pressure. 

While the risk of clotting is very small, extra caution should be practiced by those with heart conditions or concerns surrounding clotting. The increase in blood pressure can place unnecessary stress on your cardiovascular system. Nevertheless, blood flow restriction exercises have been shown to be safe for the general population.

Due to cell swelling, some musculoskeletal effects may occur. For example, bruising in the area, numbness, discomfort, abrasions on the skin, and likely delayed onset muscle soreness. However, these concerns aren’t serious, and the benefits outweigh them considerably. If you have any concerns, a physical therapist or health care professional can help you with vascular occlusion.

Warming Up for BFR

Warming up is important if you’re looking to get the most you can out of a workout. Most warm-ups are done at a significantly lighter weight than your 1 RM—anywhere from 30 to 50 percent, for most people. This is the weight range that most BFR routines tend to stick to as well, which begs the question: do we need to warm up beforehand?

The answer is yes. Not only does your body practice going through the movement, allowing for better form, but it’ll also get your heart pumping and primed for the exertion ahead. It’s a good idea to do some light cardio beforehand, for example. And before you actually get into the BFR exercise, do around 15 reps of the movement without having the blood flow restriction.

Use of BFR with Other Workouts

Even with all of its purported benefits, does this mean your entire workout should consist of BFR exercises? You’ll likely stand to benefit more from a routine that involves high-intensity training along with BFR exercises as a modality. However, this also depends on what exactly your goals are—whether they be strength, aesthetics, or a mix of the two. 

However, it’s been shown that BFR is great for muscle growth both by itself and with heavier training regimes. The benefit of BFR is that you can also use it during deloading phases of training when you give your muscles a break for heavy strength training to heal and grow.

Since BFR places relatively lower levels of stress on your joints and muscles, you can squeeze more out of your deloading phases while still taking things a lot easier. This means that BFR can be a good method of adding some extra volume on recovery days, allowing for extra muscle development.

Additionally, BFR movements can be a great way of finishing your workout, regardless of your training routine. Many studies have shown that ending with a finisher that utilizes high-reps and lower volumes, can effectively boost muscle growth and strength gains.

This holds true even when compared to a heavy-weight exercise as a finisher. All in all, BFR can add a lot to your physique and your strength over the long term. However, it’s important to support this type of training with a healthy lifestyle. 

BFR to Turbocharge Muscle Hypertrophy

Properly implemented into your routine, BFR can give you that extra edge when it comes to building bigger, stronger muscles. And if you’re trying to work around an injury, then the benefits of BFR can go even further. However, it’s still super important to support this training with a lifestyle that puts your health at the forefront.

It’s often said that you can’t out-train a bad diet, and this goes double when considering BFR. This type of training is, after all, only meant to as a way to give you an edge. It’s not going to carry a bad workout routine or a bad diet—only improve it slightly so you’re not leaving any gains on the table.

When it comes to diet and working out at higher volumes with BFR, you’re going to want to ensure you’re eating enough protein to support muscle growth. A good way to do this is by drinking  high-quality whey protein.

However, it’s also necessary to balance out the protein with vitamins and minerals from vegetables, healthy sources of fat, and complex carbs.

On top of diet, rest is the next most important thing. Especially considering high-volume workouts that utilize BFR, your muscles are going to need plenty of time to recover. We often forget that it’s actually during recovery when our muscle fibers grow back stronger and larger, which makes proper rest an extremely important part of a healthy lifestyle. Even with the best BFR routine in the world, you’ll never be able to see consistent gains without the recovery to back your training up.

Put together, these things will ensure that your body develops consistently, healthily, and over the long term. BFR is a fantastic tool to utilize, but it’s one of many aspects that should be optimized in a good routine.