It was Christmas of 2008. My brother Gabe, the other Dr. Wilson, gave me a gift. I opened it and found a pair of knee wraps. I asked, “Gabe, why in the heck would you give me knee wraps, which I don’t use?” He then explained that they were to restrict blood flow while I trained. It sounded strange, but I put my trust in my brother. Following his directions, I wrapped the knee wraps around my upper arms the next time I trained. I had never felt a pump like that before! I mean, my arms swelled up like a balloon.
Since this time BFR training has become increasingly more popular and controversial; however, that doesn’t mean that it’s any more understood. In fact, given the many different names (occlusion training, hypoxic training, KAATSU, etc.), styles (bands, cuffs, ace bandages), and goals that get associated with this type of training, the confusion seems to be growing! After researching BFR for years and studying it firsthand in the lab, I believe it has a lot to offer to a wide range of people who want gain muscle, increase training frequency and just change things up a bit in their programming. Researchers have been digging into the details of BFR for decades, but there’s also fascinating new research happening in this area all the time. Therefore, I’m devoting this installment article to answering the most common questions I hear about BFR.
What is Blood Flow Restriction and How Does it Work?
In short, BFR involves wrapping a device such as a pressure cuff, KAATSU device, or even knee wraps around the top portion of a limb in order to elicit restriction of blood flow to the working muscle. During properly performed BFR, blood is able to enter the muscle via arterial flow; however, the veins are restricted so that blood is partially restricted from leaving the working muscle; which will be explained more in depth below.
This allows for a swelling effect of the muscle, which is the first way muscles grow (Loenneke et al., 2012; Abe et al., 2008; Wilson et al., 2012). Secondly, blood flow restriction causes a buildup of metabolites in the muscle such as lactic acid. These metabolites have been shown to directly stimulate muscle growth (Loenneke, Wilson, & Wilson, 2010). Finally, the direct fatigue caused to the muscle forces the nervous system to recruit the largest fast twitch muscle fibers, which have the greatest capacity to GROW! (Loenneke, Wilson, & Wilson, 2010).
Is a Warm-up or Cool-down Necessary?
The overall purpose of a warm-up is to increase the temperature within a muscle, decrease the viscosity (thickness) of the intramuscular fluid, and prepare the nervous system for high-intensity movements. Ultimately, individuals seek to improve range of motion and performance through these activities (Wilson et al., 2012). Warm-ups can be classified as general or specific. General includes light activity such as walking on a treadmill for 10 minutes or very moderate cycling type activities. Specific warm-ups involve pyramiding up with the exercise itself. For example, if I can bench press 225 for 10, I might first lift 135 and then 185 for reps. A study from a researcher in my lab, Dr. Carlos Ugrinowitsch, demonstrated that for performance it’s best to perform a combination of a general followed by a specific warm up (Abad et al., 2011). BFR is performed at intensities normally used at the beginning of a specific warm up (30-50% 1RM). I would recommend a light, general warm-up (5 minutes), followed by a specific unwrapped warm up for 15 repetitions with the weight you will use for your first set of BFR.
What should I use to wrap with and how tight should I wrap?
Traditionally, BFR involves the use of a specialized inflatable cuff, known as the KAATSU device to restrict venous blood flow. The advantages to a KAATSU device is that you can precisely control the pressure and always replicate it on workouts. Another advantage is that you can program the device to intermittently tighten and loosen while training. This could be beneficial, for example, if you have to sit for a long period of time or are injured. By intermittently tightening and loosening you can get the anabolic benefits of cell swelling, when not training.
Unfortunately, most individuals do not have access to this sophisticated device, which has led our lab to complete extensive research on what is known as practical BFR (pBFR). Practical BFR involves the use of an elastic wrap to restrict blood flow. In studies, we have used knee and elbow wraps, however ace bandages can also be used. While practical, one concern is that you may restrict both the arteries and veins (Wilson et al., 2013; Lowery et al., 2014). Recall that arteries bring blood to the muscle, while veins take blood away. To get the maximal swelling response you want blood coming to the muscle and staying there. Thus, we want to restrict blood flow to the veins, but NOT occlude the arteries. This is important to understand because potential negatives resulting from BFR stem from fully occluding both the veins and arteries. In fact, there is evidence that wrapping tight enough to cause arterial occlusion may actually decrease muscle growth at the site wrapped (Kacin et al., 2011).
To solve this problem our lab looked at the effects of perceived pressure on blood flow during pBFR. We used knee wraps on the legs and wrapped subjects at a perceived pressure of 0, 7, and 10 out of 10 with 10 being the tightest you could wrap. We found that for the legs, pBFR at a perceived pressure of 7 out of 10 resulted in venous, but not arterial restriction. We also found that when training under this pressure the subjects drastically increased cell swelling, recruited more muscle, and had a larger amount of metabolic stress! However, it is important to note that at a perceived pressure of 10 out of 10, both venous and arterial blood flow were totally restricted! For more information on this please see our Project Mass video on BFR.
Another question is, where should you wrap and how wide should you wrap? Research has shown that lower limb cuff width (2-3.5 inches) reduces the risk of occluding the arteries compared to a wider cuff or wrap (5+ inches) (Loenneke et al., 2012). Due to this, we recommend wrapping at the top of the legs or arms in a layered manner rather than wrapping in a spiral manner all the way down the arm or leg. Finally, it is important to realize that the size of your arms or legs will also determine how tightly you should wrap (Loenneke et al., 2012). Research shows that smaller limbs have a greater probability of being occluded. As such we would recommend wrapping at a 7 out of 10 on the legs and a 6 out of 10 on the arms.
How heavy should I lift with BFR?
The primary advantage to BFR is that you can increase muscle size at very low intensities. In fact, Dr. Abe et al. (2006) found that individuals who walked with BFR at low intensities could actually increase muscle size! However, we have found that resistance training results in greater benefits in muscle and strength than walking (Loenneke et al., 2012). So how heavy should you lift? Research has shown gains with as little as 20% of your 1RM! However, muscle growth, in this case, is primarily caused in the slow and not fast twitch fibers. One study compared moderate pressure BFR with 20%, 30%, and 40% of subjects 1RM.
They found that fast twitch muscle fibers were not maximally recruited until 40% of their 1RM. However, other research has shown that lifting at 80% 1RM compared to 40% does not increase muscle fiber recruitment (Takarada et al., 2000). In addition, there is less metabolic stress. As such for maximal muscle growth, BFR should likely be performed at approximately 40% to likely no more than 50% 1RM. However, an individual is extremely sore and using BFR as a recovery day, then either walking or performing resistance training at 20-30% of their 1RM will likely still result in benefits in the slow twitch fibers. This could be important as these fibers are often difficult to hypertrophy.
How about bodyweight squats or calf raises for leg day?
When performing a 1RM squat it is important to realize that part of the resistance you are lifting is derived from your own body weight. In research, scientists generally subtract out the weight of the lower leg, which on average is about 12% of a typical individual’s body weight. Recall that BFR is optimally performed at 40% of your 1RM, but still works at weights below this. Thus, the effectiveness of bodyweight squats will likely depend on how strong you actually are. If you have a 100 pound female for example, who can squat 135 pounds for one repetition, then bodyweight squats may be ideal. By adding her body weight subtract 12% (100 -12 lbs) and adding it to 135 you get roughly 225 total lbs. Thus, her body weight is very close to 40% of her 1RM. In this case, bodyweight would likely optimize BFR training. If however an individual weighed 200 lbs and squatted 400, then their body weight minus their lower limbs (176 lbs) would account for approximately 30% of the load. In this case, bodyweight would likely recruit 40-60% of the fast twitch fibers but primarily rely on slower twitch muscle fibers. In conclusion, it all depends on your baseline strength as well as actual body weight. What I can tell you is that you can most likely increase muscle size in this way.
Is it better to be “just a little too loose” or “just a little too tight?”
This is a great question. I spoke with Dr. Carlos Ugrinowitsch about this very topic. He is actually one of the first scientists to study the molecular mechanisms of BFR and I’m fortunate enough to have worked with him. Carlos and his colleagues did a study where they first increased pressure on their study subjects to actually occlude the arteries (Lixandrao & Ugrinowitsch et al., in press). Say for simplicity this pressure was 100 units, or from a practical BFR standpoint, it would be wrapped at a 10 out 10. They then looked at individuals who trained at 20% and 40% of their 1RM. They placed the cuff on subjects and pumped up the pressure so it was either 40% or 80% of their occlusion pressure. Again from a practical BFR, it would be like wrapping at a 4 or 8 out of 10. They found that the 40% increased muscle growth the most, compared to the 20%. This makes perfect sense in light of the evidence I presented earlier. However, here is the cool thing; Both the 40% and 80 % occlusion pressures at 40% 1RM produced the same amount of muscle growth and strength gains! Therefore, it’s better to be a little loose compared to too tight. This is because as long as you reach a moderate pressure at a percent intensity approaching 40% to 50% 1RM, you should be fine. However, if wrapping too tight you run the risk of complete arterial occlusion (Wilson et al., 2013).
Is there any appreciable difference to using light dumbbells or barbells vs elastic bands for BFR arm work?
There are distinct differences between elastic and free weight resistance. When we lift a weight we are moving it along a given range of motion across our strength curve. For example, when squatting or performing leg press we are weakest at the bottom of the lift and strongest at the top. This is because we have the greatest mechanical advantage near the top range of the motion. This is similar with biceps curls; it’s always harder to curl the weight at the beginning rather than at the end of the lift. The advantage of using elastic resistance is that as the band is stretched the force increases. This means that when your mechanical advantage is greatest the force on the bands is also greatest and vice versa. Our lab has actually found that adding bands to a normal periodized resistance training program may increase lean mass ( Joy et al., 2013).
One of the keys to using BFR is to pump as much blood into the muscle as possible. This requires a high number of continuous repetitions, with minimizing rest time. One temptation when lifting free weights is to rest then pause at the top of the lift. We have been running small pilot work in our lab and found less tendency to rest then pause when adding bands to a leg press, likely due to the increased load at the top. While further research is needed, it may be that elastic resistance either on its own or with free weights may be a beneficial option when using BFR.
Are there any effects on non-restricted limb muscles?
Many people think that BFR training is just for the arms and the legs, but can it be used for the chest, back, and glutes? The short answer is yes, there is an increase in muscle mass in the non-restricted limb muscle (Yasuda et al., 2010; Madarame et al., 2008). How can this be? Simply put, by wrapping the arms or legs, the nervous system senses extreme fatigue in the limbs. As such your body is going to do whatever it can to maintain force and keep itself from failing. To compensate, your nervous system recruits more muscle from non-restricted limbs. For example, Dr. Yasuda found that restricting blood flow to the arms and performing bench press actually resulted in a 16% increase in muscle activation of the pecs! What is also interesting, is research has found that individuals who train their legs with BFR and follow it with an arm workout, actually get more growth in the arms then training them separately! While the reason for this is unclear, it is possible that growth factors released from BFR and or circulating metabolites are acting to enhance the metabolic effects in the non-BFR arms. Thus, training chest, back or glutes with the arms or legs restricted may be beneficial for inducing growth in those muscles!
What are the recovery demands of this vs other isolation training?
Our lab was the first to study the effects of practical BFR on recovery demands compared to non-BFR low-intensity training (Wilson et al., 2013). We found that, while BFR caused greater fatigue immediately after the exercise bout, 24 hours after there were no increases in muscle damage or declines in force or power. Since this type of training has low recovery demands compared to high-intensity training, it is likely that it can be performed up to every other day, but likely not more than this. In fact, we actually found that 2 to 3 days of BFR was best for gains in strength and muscle (Loenneke & Wilson, 2012). However, BFR training requires individuals to train with very high repetitions (15-30 reps). If you are unaccustomed to such high reps, then that by itself may lead to muscle damage (Wernbom et al., 2012). However, it is unlikely that the wraps themselves are increasing recovery demands. Thus, if you are new to BFR and metabolically demanding training, I would recommend using it once to twice a week. Once adapted, you can use it up to three times a week for a lagging body part.
What’s better: To do BFR-work only for arms for a few weeks and switch to something else, or to alternate strength/hypertrophy/BFR days like you recommend in project mass?
Ryan Lowery and I actually did a study on this question a few years ago using practical BFR (Lowery et al., 2014). We found that periodizing with BFR for a few weeks followed by high-intensity exercise resulted in a lot of muscle growth.
However, the rate that you periodize should be dependent on your training status (Monteiro et al., 2009). Based on past periodization research, If you are just starting out it will likely work just as good alternating every few weeks as it would alternating every day (Buford et al., 2007). However, as your training experience increases, I’d recommend using the project mass plan and switch it up every few workouts instead (Monteiro et al., 2009).
Is it necessary or advisable to go to failure with BFR?
Recall that one of the major mechanisms you grow when using BFR is by recruiting the larger, fast twitch muscle fibers. Fast twitch muscle fibers are activated by heavy resistance or fatigue (Fallentin et al., 1993). Research shows that the closer you get to near failure, the greater fast twitch muscle fiber recruitment becomes (Fallentin et al., 1993; Garland et al., 1994). As such, failure under low-intensity conditions is likely a prerequisite to optimal muscle fiber recruitment when using BFR. However, we also know that failure can be very centrally fatiguing (Ahtiainen et al., 2003). Thus, we recommend saving failure for your final set as opposed to every set of BFR (see my article on failure training). You might begin with 30 repetitions at 40% of your 1RM, rest 30 seconds, hit 15, repeat, and finally, go to failure.
Say I’m no bodybuilder, but just a guy or girl who wants some nice, shapely arms. Is 2-3 BFR sessions a week enough for me to see serious results?
Fortunately, a great deal of research has been done in non-bodybuilders (Loenneke & Wilson, 2012). In these populations we have found that 2-3 workouts with BFR a week is perfect. So the answer is absolutely!
Should I just do a couple of movements or a whole BFR workout?
This is a great question. The answer is that most of the studies have looked at BFR on its own (Loenneke et al., 2012). Our lab has teamed up with Bill Campbell’s lab on two studies (Lowery et al., 2014; O’Halloran et al., 2014) to investigate the effects of BFR combined with high-intensity resistance training. In both studies, we found that BFR in combination with high-intensity exercise was an effective method for increasing muscle mass. What’s interesting is that in the second study, we replaced 60% of high-intensity training with BFR and found that subjects were still able to increase muscle mass just as effectively as 100% high-intensity training. There are a few take home messages I want to address here. First, BFR as a stand-alone or in combination with high-intensity exercise can increase muscle growth. Second, because BFR causes very little muscle damage, it can be used during deloading periods to supplement as much as 60% of the high-intensity workload. This will give athletes the ability to still progress while allowing their joints and or injuries to heal. As such, I recommend using BFR as either a light recovery day on its own, as a method to deload and heal, or as a method to finish the muscle at the end of a workout. The finisher method is supported by studies showing that a heavy workout, which incorporates a very high repetition set at the end performed at 50% of your 1RM, can increase hypertrophy and strength compared to only high-intensity exercise alone (Goto et al., 2004).
Are there any lifts that are completely inappropriate for BFR?
Generally, I would say Olympic lifts because the skill of Olympic lifting is likely optimized under lower repetition conditions. However, with the advent of CrossFit which calls for extremely high repetition Olympic lifts, I would say that for these athletes even these lifts are not off limits. As such, you can technically use BFR for most exercises.
Are there supplements that dovetail really well with this style of training?
Any supplement which can potentially increase the cell swelling/pump response could theoretically improve BFR training. Two ways to do this would be to increase blood flow to the muscle and/or to increase the concentration of certain metabolites in the muscle. The classic blood flow enhancing agents to date include Citrulline, Arginine, and ATP (Jager et al., 2014; Preli et al., 2002). Citrulline and Arginine serve as the raw material to form Nitric Oxide (Schwedhelm et al., 2007). Nitric Oxide increases two kinds of blood flow. The first is called bulk flow. Bulk flow is when overall blood flow increases to a muscle. The second is called nutritive flow, which occurs when small vessels called capillaries are opened up. Nutritive flow, as the name suggests, is responsible for direct uptake of nutrients into the muscle. Nitric Oxide seems to increase both types of blood flow during rest, but only Nutritive and not Bulk flow during exercise (Hickner et al., 1997). However, our lab and others have found that ATP at least increases bulk flow (Gonzalez-Alonso et al., 2002; Jager et al., 2014). The efficacious doses for these supplements include 6-8 grams a day of arginine or citrulline (in form of 1:1 citrulline malate) consumed prior to training. However, there is evidence that you should cycle off these supplements for a few weeks following 4-6 weeks of use (Clark et al., 2000). For ATP, the efficacious dose appears to be 400 mg given 30 minutes prior to your workout (Jager et al., 2014).
The second method I discussed was increasing intramuscular metabolites, also called osmolytes. Osmolites work by drawing fluid into the cell. Creatine, for example, is an osmolyte, as is glycogen (Cooper et al., 2012). One of the most effective osmolytes is glycerol. Glycerol forms the backbone of triglycerides (fat). When supplemented with alone, it drastically increases intracellular fluid retention (Cooper et al., 2012). There are two primary forms of glycerol. The first is glycerol monostearate (GMS). GMS is typically in the range of 3-7% free glycerol. At these low levels, individuals need to take 30-60 grams to see efficacious results (Cooper et al., 2012). The result is often times serious gastric distress (really bad upset stomach). A new less studied form is HydroMax™ which is a highly concentrated powdered glycerol (65% free molecular glycerol). As such, individuals only need to supplement with 2-3 grams. In conclusion, while no one has studied BFR combined with supplements, its effects may be better when supplementing with agents such as citrulline malate, ATP, and some forms of glycerol.
Is Blood Flow Restriction safe?
Prior to instituting any exercise program, it is important to have clearance from your physician. As such, all of the recommendations I discuss in this paper are for healthy individuals, free of disease that already safely incorporate high-intensity resistance exercise into their weekly routine. While the safety and potential benefits of BFR in clinical populations are actively being studied (Madarame et al., 2013; Gualano et al., 2010; Karabulut et al., 2010) its discussion is beyond the scope of this article. When discussing the safety of any technique, it’s ideal to compare it to something we are all familiar with. Moreover, because the cardiovascular and nervous systems are generally the primary concerns. I will specifically compare how these systems respond in traditional resistance exercise versus BFR.
Cardiovascular and Pressure Responses
In dealing with the cardiovascular system, it has been proposed that restricting blood flow causes damage to veins and ultimately impairs long-term blood flow. However, research shows that while blood flow is restricted in the short term (during exercise) that over time (4 weeks) there is an actual increase in the ability to vasodilate and increase blood flow compared to traditional resistance training alone (Patterson et al., 2010). Moreover, with heavy resistance training (80-100% 1 RM) mean arterial blood pressure has been shown to more than double with heart rates reaching maximal levels (MacDougall et al., 1985, 1991). However, research on low-intensity BFR has only increased blood pressure and heart rate by 11-13% (Takano et al., 2005). As such traditional resistance exercise results in much greater blood pressure, heart rate, and even cardiac output changes than low-intensity BFR.
Why the drastic differences? You should understand that when doing BFR with low-intensity exercise that studies have applied pressures around the limb ranging from 50 to 230 mmHg (Loenneke & Fahs et al., 2012). However, during maximal high-intensity exercise, the muscles are contracting so hard that intramuscular pressures average around 500 mmHg and have been recorded as high as over 1000 mmHg (Sylvest et al., 1959; Sejersted et al., 1984)! This is important to understand as in general complete arterial restriction occurs at a range of 140 to 235 mmHg of an externally applied pressure (Loenneke et al., 2012). Moreover, complete blockage of blood flow has been shown to occur with traditional resistance exercise with as low as 50% and 64% of individuals 1RM. As such, it is important to realize that traditional resistance exercise already results in occlusion of blood vessels during even moderate force contractions. Therefore, BFR is in part mimicking the effects of high-intensity training at a low-intensity.
Another concern with BFR is that it may cause thrombosis. Thrombosis is the formation of a blood clot inside a blood vessel, which obstructs blood flow. The three major factors thought to cause this are a hyper-ability to form a blood clot (Hypercoagulability), vascular damage, and vascular occlusion of blood flow. It is important when using BFR that you restrict but do not completely occlude arterial flow. Secondly, it is also important to know that the formation of a clot is caused by the imbalance between coagulation and fibrinolytic (the breakdown of coagulation products) processes. Research with low-intensity BFR has shown that this type of activity does not increase coagulation and may actually increase the breakdown of clots (e.g. increase fibrinolytic activity) (Takano et al., 2005; Clark et al., 2010; Fry et al., 2010).
The nervous system’s response to BFR training is an additional topic of discussion. In a survey conducted by Nakajima in 2010, a small percentage of BFR training sessions led to numbness in the wrapped limb. This leads to the implication that BFR could be too taxing on the nervous system; however, further studies looking at nerve conduction velocity (speed at which a nerve impulse is transmitted) saw no change following 4 weeks of BFR at 30% 1RM (Clark et al., 2010). This could lead to the assumption that several of the BFR training sessions that led to numbness could have been a result of improper wrapping techniques.