Introduction To Blood Flow Restriction (BFR) Training

“You can get stronger and gain muscle by lifting light weights”  seems like a clickbait-y type of claim, but would you be surprised to learn there’s some legitimate (and not-so legitimate) science to support a training method to do just that?

Enter Blood Flow Restriction Training.  

Blood Flow Restriction (BFR) dates back to the 1960’s, when Dr. Yoshiaki Sato used small rubberized bands as tourniquets at the top of his arms and legs during the limited exercise he could do while recovering from an injury. By reducing the blood flow, he thought, he could stimulate the muscles effectively and not only limit muscle loss, but also speed up his recovery. As the story goes, Dr. Sato reported that his method worked well and subsequently patented it as Kaatsu training.¹ Over the last 20 years or so, BFR has become a popular training method in not only sport, but also in rehabilitation settings. 

If tying off body parts for gains sounds like a good time or you would like to know more about it first, you’re in the right place. In this article, we’ll cover important concepts surrounding BFR like what it is, whether or not it works, and how-to do it. Let’s start out by defining BFR.

What is Blood Flow Restriction (BFR)?

Blood Flow Restriction (BFR) is a training technique that involves restricting venous blood flow from a working muscle while allowing arterial blood flow into the muscle. This is typically achieved using a cuff or band placed around the proximal portion of the limb.

Blood flow starts with the beating heart, which pumps out blood to the organs and tissue through arteries, and then returns to the heart through veins. Blood pressure measures the force of the blood in our arteries when the heart is contracting, e.g. the “systolic” phase of the cardiac cycle (the top number), and the blood’s force in our arteries when the heart is relaxing, e.g. the “diastolic” phase of the cardiac cycle (the “bottom” number). A blood pressure measurement of 120 mmHg / 80 mmHg refers to 120mmHg systolic over 80 mmHg diastolic. The higher pressure in the arteries compared to the veins facilitates flow of blood through the vessels of our body.

Now, suppose you placed a cuff or wrap to your arm or leg with a bit of pressure to squeeze the blood vessels in that limb. If applied tightly enough to squeeze only the veins, but not the arteries, more blood enters the limb than can exit. This causes a bit of a traffic jam in the blood vessels, delaying the oxygen and energy delivery to the working muscle in the occluded limb. This is the technique used with BFR in order to create an environment conducive to increases in muscle size and strength. ^2-11

How Does BFR Work?

Let’s go over the 3 most likely ways BFR has an effect on muscle growth (hypertrophy) and muscle strength.

Metabolic Stress

Metabolic stress  is essentially the accumulation of biochemical byproducts like hydrogen and inorganic phosphate ions, which occurs when some of the energy stores within the muscle get low during exercise. It’s what is most commonly attributed to the “burn” you feel in muscles when they are working.¹⁸ 

In general, anytime muscles are contracting during resistance training, they’re producing these metabolites, making it hard to determine whether metabolites contribute to hypertrophy or if it’s just the mechanical force from muscular contractions. Based on the present data, it appears the majority of muscular hypertrophy is caused by mechanical signals, whereas metabolites may have an indirect role. 

Because low loads are used in BFR, tension in the muscle is not as comparable to that of conventional resistance training and BFR has been shown to cause virtually no muscle damage.²⁰ This actually may be one of the other reasons it works, as muscle hypertrophy, e.g. increased muscle fiber size, occurs when muscle protein synthesis exceeds muscle protein breakdown. In other words, hypertrophy seems to lag until muscle protein breakdown is minimized and muscle protein synthesis predominates. ^37,38

Metabolic stress is one of the likely mechanisms by which BFR works, though it’s not a slam dunk. Existing evidence is conflicting regarding this topic, as there does not seem to be conclusive advantages of using continuous BFR versus intermittent BFR.^5,35,36

Motor Unit Recruitment

A motor unit is the nerve cell and all the muscle cells or fibers it has an effect on. When lifting heavier loads (above 65% of 1 RM), many of these motor units are recruited to help overcome the force required to resist or move the external load. However, with BFR, similar amounts of motor units are recruited with significantly lower loads.^5,21 The ability to recruit more motor units significantly contributes to strength and is the most likely reason for gains in strength seen with the use of BFR. 

Cellular Swelling and Cellular Hypertrophy Signaling

Cell swelling, in the case of BFR, is most likely the result of restricting blood flow out of the limb, causing muscle cells to swell. This swelling is thought to have a potential effect on muscle hypertrophy.^22,23 What is proposed in theory, is that this swelling leads to a number of other cellular mechanisms that are anabolic in nature (muscle growing).^24-26 For a further dive, you can check out this review. Though not clear yet, cell swelling may contribute to the mechanisms leading to increase in muscle size over time.

Hormonal Signaling 

As one small bonus, there are potential hormonal contributions that may be worth mentioning here. For example, there is a significant increase in growth hormone release following BFR²¹, though the impact on hypertrophy is unclear and shouldn’t be considered a primary factor at this time. For now, this is more of an interesting phenomenon but shouldn’t be considered as being a significant contributor to the effects seen with BFR.

How-To Do Blood Flow Restriction Training?

The band or wrap used in BFR training is typically applied as high up on the limb as possible. In research and healthcare settings, a specialized cuff that can measure blood pressure is often used in an effort to reduce the risk of either the cuff being too tight and occluding arterial blood flow which could be harmful, or the cuff being too loose and not delivering the intended result. However, more practical applications can be applied and will be discussed later. It should be noted here that BFR has been shown to be quite safe across different populations, limb locations, and pressures in both relatively short and long-term applications.^12-18

The loads lifted while using BFR are low compared to conventional resistance training. As a general guide, conventional resistance training is performed with loads at or above 60-65% of a 1-repetition-maximum (1RM) for sets of 1- to 20-repetitions, followed by rest periods of 2- to 5-minutes.

In contrast, the most commonly used scheme in BFR is a set of 30 repetitions, followed by 3 sets of 15 reps with 30-60 seconds of rest between sets with loads between 20-30% of 1 RM.^2-3 This protocol is sure to give you a juicy pump. You may feel that you have, for the first time, connected to what the great physique competitors of our era have been chasing and you are now on your war-path to the Olympia stage.

Blood Flow Restriction For Strength Training

If BFR does all this great stuff, then why aren’t we all using it in every training session?  First, a conventional approach to strength training is still going to be the most valuable stimulus for hypertrophy and strength gains. While BFR has been shown to yield similar results in hypertrophy when compared to conventional resistance training, it is unknown exactly how long these results can be expected as it is possible there are diminishing returns with continuous use over time. In isolation, BFR has an overall smaller effect size than conventional resistance training, though this effect may be different when BFR is combined with conventional training.⁶

If BFR gives you a massive pump, it likely comes as no surprise that it has an effect on hypertrophy. What is surprising, however, is that improvement in strength seems to be the same or even better when BFR is combined with conventional strength training interventions.^8-10 This is most likely due to the recruitment of additional motor units when using BFR despite the lower relative loads. For this reason, BFR may likely be an appropriate addition to a conventional training program where heavier loads are being lifted for part of the training session and BFR with low loads is utilized the other part of the training session.

Blood Flow Restriction For Injury Rehabilitation

BFR is often used in a rehabilitative setting as heavier loads may be unavailable, may be contraindicated following procedures, or cannot be tolerated well due to pain or instability. It has been shown that patients in these settings lose less muscle over time even when BFR is applied passively without exercise being performed²⁸. Following procedures or injury, BFR has been successfully used to minimize muscle loss, improve strength, and improve measurements related to returning to sport or activity⁴. It should be noted that when compared to rehabilitation without BFR, the BFR groups do tend to outperform the non-BFR groups.

As mentioned before, it is important to remember that BFR has been shown to provide greater benefits in strength when combined with conventional resistance training. For this reason, BFR should not be a stand-alone intervention for too long following an injury if you are looking to maximize the benefits of a well-rounded rehabilitative program. If considering the use of BFR in your rehabilitation, please consult with your healthcare provider before adding this intervention to your personal toolbox. 

Blood Flow Restriction For Recovery

A final potential benefit of BFR may be for its use as a recovery modality. Oddly, this idea stems from research on the heart. It has been shown that repeated bouts of starving the heart of oxygen and then reperfusing it with oxygen-rich blood has a positive effect on cardiac tissue health.³⁰ This idea was then taken further to assess the effect of passively occluding blood flow to muscle tissue for 2 bouts of 3 minutes following intense exercise and letting the blood naturally flow through the limb for 3 minutes between sets.²⁹ What’s great about this study is that they measured objective outcomes like jump and sprint performance 5 minutes and 24 hours after this intervention instead of something more subjective like soreness. In this study, it was shown that the passive BFR following intense exercise had some positive effects with the majority of these effects happening 24 hours after the intervention. Though this evidence may not be incredibly strong and caution should be taken in the interpretation of the results.

While there are still more questions than answers and we are far from certainty, we do have some small sample data suggesting that there may be potential benefits to using BFR for recovery of muscle function following intense bouts of exercise which may be of future interest.

When Should Blood Flow Restriction Be Used?

As mentioned earlier, many research and clinical settings use specialized cuffs with digital measurement of blood pressure to more accurately use pressures that fit the individual. For example, to occlude the veins of one individual with a higher blood pressure by 80%, this amount of pressure in the cuff will be different when compared to someone with lower blood pressure to achieve the same degree of venous occlusion. The amount of pressure needed to occlude veins will also depend on the size of the limb and differences in lean mass will affect the needed pressures to obtain the same relative amount of flow restriction. 

That said, things like knee wraps and elastic bands have also been safely and effectively implemented in training and rehabilitation settings. A perceived 7 out of 10 that is “snug, but not painful pressure” has previously been used in practical settings³¹. It seems that in studies, as well as from practical experience, that higher pressures are better tolerated on the legs than the arms which is likely due to the generally larger size of the limb and vessels there. 

After speaking with your healthcare provider, you can purchase specialized cuffs, simply use wraps, or use elastic bands to place a 7 out of 10 pressure high up on the limb being trained. Then, perform 3-4 sets of 15-30 reps with a load that is something around 30% of a 1 RM for the movement you are about to perform while resting somewhere between 30 and 60 seconds between sets. As there is conflicting evidence, it doesn’t seem to make a considerable difference whether the cuff is kept on or released between sets (continuous vs. intermittent BFR) in respect to muscle hypertrophy or strength. However, intermittent BFR is less uncomfortable and typically tolerated better. 

Finally, here are a few pro-tips for using BFR. First, it seems that using BFR for exercises that require a fairly large range of motion tends to be better. For example, a full squat with BFR would yield better results than a quarter squat. Second, while the use of BFR has been shown to be safe across multiple populations, when not using specialized cuffs, a few considerations to ensure safe use are important. For example, the width of the wrap will significantly affect the occlusion pressure and thicker wraps have a higher tendency to occlude arterial blood flow. So, using a thicker wrap will require less pressure and in general, a smaller width is preferred to reduce the likelihood of occluding arteries. Since you will not be completely occluding blood flow, the pressure should not become painful. That said, BFR training is absolutely brutal and the muscular pump you feel will be fairly intense, similar to a normal set to failure.

While practical uses are available and effective, again, please consult with your healthcare provider before implementing BFR to be sure that you are not wrapping your occlusion method too tight or for too long. 

BFR Summary

BFR seems to have a positive effect on hypertrophy and strength in both trained and untrained individuals^32-34. BFR is safe, causes little to no muscle damage, and is easy to recover from. In fact, it may aid recovery. For this reason, you don’t need to change your programming much to work BFR in. However, if your normal training is wearing you down, BFR can be a solid substitution for some of your training volume to continue maximizing strength and hypertrophy gains while backing off of more frequent or higher volumes of heavier, conventional lifting. 

Similarly, BFR can be extremely beneficial in the context of rehabilitation whether performing exercise with them on or passively having limbs occluded for several bouts. This can be beneficial when unable to lift heavier loads due to surgical precautions or due to discomfort with heavier loads. In general, when using BFR in a rehabilitative context, it is highly recommended to work with a healthcare professional when starting out. 

Whether used for additional gains in regular training or in the rehabilitation of a musculoskeletal injury, BFR seems to be a safe and practical tool to improve strength and hypertrophy across diverse populations.

Folks, that’s a wrap!