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Fun With Tourniquets: Blood Flow Restriction Training

Nov 03, 2022

 

What is Blood Flow Restriction Training? 

 

Blood flow restriction training (BFR) is a method of training that has rapidly gained popularity in the last 5-10 years both in the athletic performance and rehab spaces. However, it is not actually a new concept - experimentation with BFR began over 50 years ago, and it has been extensively studied and refined since then.

 

Put simply, BFR involves the application of tourniquets around the arms or legs while lifting weights or performing low intensity aerobic activities. The tourniquets are usually set to a specific individualized pressure that prevents venous blood flow from leaving the limbs but does not completely occlude arterial blood flow into the limbs. For resistance training, the pressure is typically applied for several sets of each exercise and then released in between exercises to allow blood flow to reperfuse the limbs. For low intensity aerobic activities, the pressure is usually applied in bouts of 8-10 minutes at a time and released for at least 60 seconds in between bouts. 

 

What Does BFR Do? 

(Science incoming. If you’re only interested in why and how to use BFR, this section can be skipped)

 

The goal of blood flow restriction training is generally to promote muscle hypertrophy (i.e. muscle growth) using very light weights that typically would be less efficient for stimulating growth.

 

Generally speaking, even without BFR, muscle growth is stimulated equally over a very wide array of loads. Anywhere from 30% of a 1 repetition maximum (1RM) up to 90+% of a 1RM when the same number of sets are done and sets are taken close to failure are equally effective for muscle growth. This means that, on average, if people do biceps curls with a light weight that allows them to hit 25 reps before failure or a heavy weight that only allows 5 reps before failure, the biceps will grow the same.2,3 However, loads below 30%1RM seem to be less efficient for stimulating muscle growth. 

 

Blood flow restriction training allows for the use of loads as low as 20% 1RM to still be equally as effective for muscle growth as heavier loads.

 

Although there are still questions about why this occurs, a likely explanation is as follows:

 

Using the biceps curl as an example, imagine you are lifting a weight that would allow for around 15 repetitions until muscular failure. Our nervous systems want to be efficient and not waste energy lifting the weight, and so our brains will only send signals to recruit the motor units (groups of muscle fibers innervated by nerves) necessary to complete the task.

 

At the beginning of the set, smaller, slower motor units are recruited in increasing amounts until the muscle is able to produce enough force to lift the weight. As the set continues, these smaller motor units produce metabolic byproducts that start to interfere with muscle contraction and cause fatigue. As the smaller motor units become unable to produce the force necessary, more motor units are recruited to continue moving the weight. These will usually be recruited in order from smallest/slowest to largest/fastest. As you reach the last few reps of the set, all of the available motor units will have been recruited and are experiencing fatigue, and eventually the muscle will be unable to contract with enough force to move the weight again, resulting in failure. This concept is known as Henneman’s Size Principle.4  At the end of the set each muscle fiber will have experienced mechanical tension, which is currently understood to be the main driving force of muscle hypertrophy.5 

 

With very light weights, i.e. weights under 30%1RM, it may be that the fatiguing byproducts can be carried away by the cardiovascular system at a rate that prevents enough muscle fatigue to result in the recruitment of all available motor units by the end of a set. It could also be the case that using very light weight for very high reps is much more difficult to take close to actual muscular failure - people may be more prone to giving up on a set early or the central nervous system may limit effort before the muscle reaches a necessary level of fatigue. Regardless of why it happens, loads under 30%1RM are less effective for stimulating hypertrophy.

 

However, the application of a tourniquet that prevents blood flow from leaving a limb during an exercise restricts the removal of metabolic byproducts by the cardiovascular system. This means that even a low load will result in a high enough concentration of fatiguing byproducts that maximal motor unit recruitment occurs, and every muscle fiber available will be recruited and exposed to significant mechanical tension similar to lifting with heavier weights. There may also be a direct effect of the metabolic byproducts on muscle hypertrophy6, although evidence is still lacking for this mechanism. 

 

The result of the blood flow restriction is that, with loads as low as 20%1RM, muscle hypertrophy is equal to that of normal resistance training.7 This has significant implications for injury rehabilitation and training load management during periods of high volume and stress. 

 

 

Why Use BFR?

 

The greatest benefit of BFR is the ability to use very light weights to stimulate the same muscle growth as with heavier weights. If a person is experiencing joint pain, tendon pain, a muscle tear, or any other number of musculoskeletal problems, they may be unable to use weights heavy enough to maintain muscle mass during the healing process. This can result in the loss of muscle (atrophy) and a longer time period before full function is restored after injury resolution. However, with BFR, injured body parts can typically still be stimulated enough that muscle mass can be maintained or even increased during the healing process. BFR can also play a huge role after something like surgery to avoid losing as much muscle and function as possible.8 

 

In addition, BFR may have benefits that go beyond just muscle mass. Some emerging research has found that tendons seem to respond to BFR the same was as they do to heavier weights, which may mean BFR is extremely useful for tendinopathies or tears.9 

 

Finally, BFR can be helpful purely for performance outside of any injuries. Generally speaking, more sets close to failure per muscle group = more muscle growth per muscle group (each set does have diminishing returns).10 However, the number of sets has to be balanced against the ability to recover from the training, and there is likely a hypothetical upper threshold for every individual at which injury becomes significantly more likely due to increasing tissue stress. As BFR training typically results in much less mechanical tissue stress on most tissues, sets that are in a training program purely for hypertrophy purposes might be able to be replaced with BFR sets for easier recovery. 

 

How To Use BFR

 

Cuff Application:

 

BFR cuffs should always be placed as high on the limb as possible. This means that for arms, the cuffs should be as close to your shoulder as they can be, and for legs they should be as high on your thighs as they can be. Even if you are performing something like calf raises, the cuff should still be placed high on the thighs. These parts of your limbs have a decent amount of tissue that protects nerves and blood vessels from potential damage from the constriction. NEVER PUT CUFFS ON ALL 4 LIMBS AT THE SAME TIME. Both arms are okay, both legs are okay, but do not occlude both arms and both legs simultaneously. There is a limited amount of blood in your body, and pooling it all in your limbs may not leave enough for other things. 

 

Cuff/Tourniquet Size:

 

There are a wide variety of cuff sizes, but it is generally accepted that wider cuffs are more comfortable than narrow cuffs. Wider cuffs are also less likely to create enough pressure to damage nerve and vascular structures underneath them. 

 

Cuff Pressure:

 

To find the optimal pressure for the cuff, first the total limb occlusion pressure must be found (the amount of pressure required to cut off all blood flow in and out of the limb). Many BFR products have an automated system to do this using doppler to measure blood flow, and it is highly recommended that one of these products are used. Next, the cuff pressure will be set to a percentage of the total limb occlusion pressure. There is evidence for the effectiveness of range of pressures - anywhere from 40% of the limb occlusion pressure to 80% have all been shown to be effective, generally safe, and well tolerated. There are some recommendations for arm pressure to be on the lower end of the scale (40-60%) and for leg pressure to be higher (60-80%), but it is likely up to the individual’s personal tolerance. Lower loads (20%1RM) may require slightly higher cuff pressure than higher loads (40%1RM) to be effective. 

 

Sets, Reps, and Rest Periods:

 

Most of the blood flow restriction literature has participants do 4 sets per exercise consisting of one set of 30 reps and 3 sets of 15 reps with 30 to 60 seconds of rest between sets. These numbers may be fairly arbitrary, but this set and rep scheme has been shown to be equally as effective for muscle growth as performing 4 sets to failure while being more comfortable and less fatiguing.12 

 

Training load: Anything from 20% 1RM to 40% 1RM has been shown to be effective for muscle growth with BFR use. The load should probably be high enough that the last set of 15 is difficult to complete. 

 

 

Potential Drawbacks

 

While blood flow restriction training can be a great tool in the right circumstances, there are some drawbacks. The first is that BFR training is a fairly uncomfortable process for many people. You’re working out with a tourniquet on your limbs, and it absolutely feels like it. 

 

The second drawback is that BFR training by itself is not as effective for strength gains as heavier load training.7 This is because strength is a combination of muscle size and the skill your nervous system has in using those muscles. When you practice the skill of lifting heavy weights, you get better at that skill. BFR is generally done with very light weights, and so while muscle mass will increase, the skill in using that muscle to lift very heavy things is not being practiced. This can be rectified by doing some heavy load training with the specific movements you want to improve in and using the BFR purely for hypertrophy accessory work.

 

The third drawback is that you can only put BFR cuffs around your limbs - you can’t put cuffs around your back musculature, abs, chest, or neck (or at least you shouldn’t). Fortunately, it does appear as if hypertrophy in muscles proximal to the cuffs does occur, but there hasn’t been much exploration how this compares to normal lifting. Shoulder musculature, gluteal muscles, and trunk musculature has been shown to hypertrophy with BFR training.13,14 However, if I had to guess, I would bet that somebody squatting without BFR with a weight that’s heavy for them will experience significantly more muscle growth in their torso musculature than somebody that is limited to the low loads they can use with BFR, even if the quads below the cuffs grow the same.

 

Finally, for people that have experienced blood clots of any kind, it may be safer to just stay away from BFR. There is not strong evidence for this stance one way or another, but when potential harm is on the line, it is likely safer to not risk it. 

 

Conclusions/Recap

 

To recap, blood flow restriction training can be an incredibly useful tool in the right situations. In many cases of pain or injury, it can help prevent muscle atrophy and result in a much quicker return to full function. For body composition and athletic performance, it can replace some of the training volume for accessory work so the trainee doesn’t beat themself up quite as much. BFR has been generally shown to be safe, effective for muscle growth, and well tolerated in most populations, and it may be worth giving it a shot. 



  1. The history and future of KAATSU training
  2. Resistance Training Load Effects on Muscle Hypertrophy and Strength Gain: Systematic Review and Network Meta-analysis 
  3. Loading Recommendations for Muscle Strength, Hypertrophy, and Local Endurance: A Re-Examination of the Repetition Continuum
  4. Assessment of size ordered recruitment.
  5. Stimuli and sensors that initiate skeletal muscle hypertrophy following resistance exercise 
  6. A review on the mechanisms of blood-flow restriction resistance training-induced muscle hypertrophy 
  7. Magnitude of Muscle Strength and Mass Adaptations Between High-Load Resistance Training Versus Low-Load Resistance Training Associated with Blood-Flow Restriction: A Systematic Review and Meta-Analysis.
  8. Use of Blood Flow Restriction Training for Postoperative Rehabilitation 
  9. Blood Flow Restriction Resistance Training in Tendon Rehabilitation: A Scoping Review on Intervention Parameters, Physiological Effects, and Outcomes
  10. A Systematic Review of The Effects of Different Resistance Training Volumes on Muscle Hypertrophy 
  11. Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety
  12. Frequent blood flow restricted training not to failure and to failure induces similar gains in myonuclei and muscle mass 
  13. Blood Flow Restriction Training for the Shoulder: A Case for Proximal Benefit
  14. Exercise intensity and muscle hypertrophy in blood flow-restricted limbs and non-restricted muscles: a brief review 

 

By Nate Jones, PT, DPT

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