If you’re in any which way connected to the rehabilitation, sports medicine, or athletic performance worlds, you’ve probably heard the word “blood flow restriction” or “BFR” at some point. A growing body of evidence now supports the use of using blood flow restriction combined with low-load resistance training to enhance hypertrophic and strength responses in skeletal muscles. Blood flow restriction training utilizes the application of an inflatable pneumatic cuff or wraps around a limb to limit the amount of blood flow available to the exercising muscle. The goal is to fully occlude venous blood flow out of the exercising limb and restrict a certain percentage of blood flow into the exercising limb.
MUSCLE HYPERTROPHY WITH LOW LOADS?
It has been generally been accepted that muscle hypertrophy requires high-load training utilizing loads of at least 70% 1-repetition max (70%RM) or lower loads (30-50%RM) until failure. However, there is mounting evidence that now supports that low-load resistance training (20-40%RM) combined with blood flow restriction can similarly induce muscle hypertrophy and strength gains. What we used to know and understand about muscle cell physiology and hypertrophy has been turned upside down through blood flow restriction research. We are learning that metabolic stress can be similarly as effective as mechanical stress in inducing hypertrophic changes.
Blood flow restriction training can be used in any situation where the goal is to increase muscle hypertrophy and strength. While we do not recommend replacing high load resistance training with blood flow restriction training, it can be used in the rehabilitation setting as a bridge to increase muscle strength and size when a person might not be able to lift heavier loads. For example, after most surgeries, there is a period of time that as rehabilitation specialists we must respect the surgical site and healing tissues and employ lower load exercises. These lower load exercises are not heavy enough to induce a hypertrophic or strength stimulus to the exercising muscle. However, by adding blood flow restriction to these same low load exercises we are able to induce significant strength and hypertrophy gains in as little as 4 weeks (it takes 8-12 weeks to gain muscle size with regular high load resistance training)! The rehabilitation setting is where we believe blood flow restriction training will have the greatest impact, speeding up recovery times and getting people stronger, faster, utilizing lower load exercises that are friendly and safe the to healing joint, tendons, or other surgically repaired tissues.
This article was written by a colleague of ours, Dalton and serves as a highlight reel of a recent systemic review titled “Exercise with Blood Flow Restriction: An Updated Evidence-Based Approach for Enhanced Muscular Development” published in the Sports Medicine Journal in 2015 by Scot et al. This review contained fantastic information and guidance as to what the current evidence base suggested to optimize blood flow restriction training applications.
This blog post is meant to be a highlight-reel of the review, offering key take-away points regarding:
- Response & Mechanisms
- Cuff Application
- Exercise Stimulus
- Practical Applications
- Limitations & Contraindications
If you read nothing else, know these key points:
A growing body of evidence now supports blood flow restriction combined with low-load (20-40% 1RM) resistance exercise can enhance morphological and strength responses1. However, some of the variables involved with blood flow restriction are becoming clearer and research is allowing them to be optimized for the best effects.
ADAPTIVE RESPONSES & POTENTIAL MECHANISMS
Using blood flow restriction, muscular hypertrophy and strength benefits are seen in both untrained and athletic populations3,4,7,8,9-15. Interestingly, blood flow restriction creates hypertrophic muscular responses without high mechanical loads, but the underpinning physiological mechanisms are not fully understood.
One theory proposes that downstream of the blood flow restriction cuff, greater accumulation of metabolites act as primary moderators of an anabolic response, due to increased production and limited removal1. Importantly, this accumulation of metabolites may increase muscle cell swelling, intramuscular anabolic/anti-catabolic signaling, and muscle fiber recruitment. Also, blood flow restriction may increase the activation and number of myogenic stem cells, enhancing the hypertrophic response16. All of these responses are thought to be beneficial for muscular adaptation.
Although there is growing interest in the mechanisms by which blood flow restriction can augment resistance training adaptation, we do not yet fully understand all of the physiological processes involved, and further research is required. However, with that said, it is now well acknowledged that blood flow restriction can enhance the adaptive responses to low-load resistance exercise and the adaptations seen are dependent on both the blood flow restriction stimulus itself and the exercise protocol performed.
One of the most important factors to consider when applying BFR is the width of the cuff. Researchers have used a range of cuff widths for both the upper and lower limbs17:
- Legs (4.5–18.5 cm)
- Arms (3–12 cm)
Wider cuffs, up to 13.5 cm, can increase ratings of pain and perceived exertion and limit exercise volume when compared with narrow cuffs, as low as 5.0 cm, when inflated to the same restrictive pressure18. Also, wider cuffs transmit pressure through soft tissue differently to narrow cuffs. Wide cuffs restrict arterial blood flow at lower pressures compared to narrow cuffs. Also, limbs with a larger circumference require higher occlusive pressures to reach the same level of arterial occlusion19. Knowing this, when implementing blood flow restriction training, it is important to consider both cuff width and limb circumference.
It is our recommendation to use a cuff that is as wide as possible, as you need less pressure to the restrict arterial inflow. A wider surface area means lower pressure distributed below the cuff – potentially a safer environment for the more delicate neurovascular structures that are also below the skin.
Another important variable involves the pressure used through the blood flow restriction cuff. Optimal blood flow restriction pressure has been hypothesized to follow a hormetic-like relationship6. If the restrictive pressure is too low, muscular responses may not be significantly augmented1. On the other hand, extremely high pressures can be a safety concern and may not enhance muscular development more than moderate pressures6. This is important to consider; if blood flow restriction stimulus or prescribed training doesn’t follow scientific rationale, sub-optimal training responses could result1.
Blood flow restriction pressure should be high enough to occlude venous return, yet low enough to maintain arterial inflow into the muscle6. Following this, blood flow restriction pressure should vary relative to each individual and be dependent on both cuff width and the size of the limb to which blood flow restriction is being applied.
Some have implemented blood flow restriction as a percentage of estimated total arterial occlusion pressure1. Pressure equivalent to 50–80% of the pressure required to occlude arterial flow is appropriate during low-load resistance exercise.
Blood flow restriction using % of total occlusive pressure can result with20:
80 % – hypertrophic and strength responses similar to traditional high-load training.
50 % – maximize EMG amplitude and increase torque of low-load knee extension exercise.
50 % – maximize acute muscle swelling and blood lactate responses.
We recommend utilizing 80% of limb occlusion pressure in the lower extremity and 50% of limb offclusion presure in the upper extremity.
The only way to calculate a relative pressure is through the use of a doppler. Shown below is an example of utilizing an external dopler with the Generation 2 SmartCuffs.
It’s extremely important to use relative pressure vs absolute pressure. Absolute pressure would the exact amount of mmHg used in the cuff to restrict blood flow whereas relative pressure represents the percentage of blood flow restricted by the cuff. From our friend Dr. Nicholas Rolnik: “Imagine using the same pressure for a geriatric client as a bodybuilder? What would you think the stimulus would be given the same pressure? Might be completely occluding arterial flow for the geriatric client but barely occluding arterial flow for the bodybuilder! This can lead to sub-optimal outcomes and increased risk of adverse events. This is why determining arterial occlusive pressure is CRITICAL to the administration of BFR. Without this knowledge that is easily obtained using a Doppler device, you are guessing and in the dark about the exact stimulus, you are applying to yourself or your clients. Be better than arbitrary. Our clients deserve better.”
EXERCISE Combined with Blood Flow Restriction
Blood flow restriction must be combined with some type of an exercise stimulus to enhance muscular development1. Even simply walking with blood flow restriction has been shown to facilitate small improvements in muscle strength and size21-23. Below you can see the evidence-based recommendations for the application of blood flow restriction with resistance training to enhance hypertrophic and strength adaptations1:
ELDERLY & POST-SURGERY:
Muscular adaptations achieved with blood flow restriction training may benefit populations with compromised strength and/or joint stability25. For example, blood flow restriction alone during periods of cast-immobilization can reduce normal muscle atrophy seen, and limit functional declines in muscular strength2,26,27.
Also, speeding up post-surgery recovery is a potential use, as using light load exercise can reduce risk of injury post-op. For example, simple walking or cycling, when combined with blood flow restriction, can lead to small yet significant improvements in the strength and size of the leg muscles21-24.
HEALTHY & ATHLETIC POPULATIONS:
Due to the low loads used with blood flow restriction and the limited muscle damage that occurs, athletes can benefit from decreased training loads, whilst still gaining a physiological stimulus for muscular adaptation. Similarly, athletes looking to increase their longevity in sport may benefit from the decreases in mechanical stress with BFR training. The changes in muscle strength following blood flow restriction training are more closely related to rapid increases in muscle hypertrophy as opposed to neural adaptations. These adaptive responses can enhance performance across a
range of athletic tasks, including maximum strength5,9,14, countermovement jump power5, maximal and repeated sprint performance5,8,14, agility performance9, and the aerobic shuttle run test9. The research data clearly demonstrates that low-load blood flow restriction training can enhance markers of physical performance in already well-trained athletes.
With blood flow restriction, the biggest concern always brought up includes safety. In a 2006 large survey of Japanese facilities employing blood flow restriction exercise28, the most common side effects included subcutaneous hemorrhage (13.1% of participants), and numbness (1.3 % of participants).
However, these symptoms are often discovered at the beginning of a blood flow restriction training program and dissipate as the individual becomes more accustomed to this training modality. To determine a participant’s level of risk during blood flow restriction exercise, Nakajima et al. have proposed a points system whereby the practitioner assigns each patient a numerical score based on the number and severity of blood flow restriction contraindications they exhibit28. This approach may be beneficial for identifying those at risk of detrimental complications during blood flow restriction, however, general contraindications and precautions should still be considered.
- History of deep-vein thrombosis
- Varicose veins
- High Blood pressure
- Cardiac Disease
- Subcutaneous hemorrhage
- “Feeling Cold”
Nonetheless, when used in a controlled environment by trained and experienced personnel, blood flow restriction training appears to provide a safe training alternative for most individuals regardless of age and training status.
Combining blood flow restriction with low-load resistance exercise enhances hypertrophic and strength responses. Although the driving adaptive mechanisms are not yet clear, blood flow restriction has important implications for individuals who cannot train using heavy loads. Well-trained athletes can benefit from low-load BFR training, either as an independent training method or in combination with traditional high-load resistance training. When implementing blood flow restriction, cuff width must be appropriate and restrictive pressure must be specific to each individual limb. Muscles of the limbs and trunk can benefit from blood flow restriction training, meaning both single- and multi-joint exercises can be prescribed for training programs. To create a sufficient physiological stimulus, training plans should include, low exercise loads (20–40 % 1RM), short inter-set rest periods (30–60 s), and relatively high training volumes (50–80 repetitions per exercise). Because blood flow restriction training does not markedly increase muscle damage, brief periods of high training frequencies may be possible. The research is starting to show the overwhelming positive effects of blood flow restriction training, especially in clinical settings aimed at rehabilitation. BFR is quickly growing in popularity and is one of the most exciting new clinical tools of the decade.
Want to come learn how to safetly and effectively utilize blood flow restrictioning training in your practice? We teach courses around the world! Check out our course dates HERE.
ABOUT THE AUTHOR: DALTON
Growing up in Oregon, Dalton graduated in 2015 with honors from Southern Oregon University earning a Pre-PT Health and Science Bachelor’s degree with a minor in Business. Following a non-traditional route, Dalton then attended Robert Gordon University in the United Kingdom, where he completed a CAPTE accredited Msc in Physical Therapy in 2018, undertaking multiple clinical rotations across Scotland and Sydney, Australia.
Currently, Dalton lives in London and works in a private orthopedic outpatient clinic called Anatomie Physiotherapy. Dalton has a passion in sports orthopedics with a focus on rehabilitation of the knee joint. In Dalton’s spare time, he practices and coaches wrestling and Brazilian jiu-jitzu, and enjoys cycling, weight training, and anything outdoors. Dalton has a strong interest in applying sports biomechanics to his extracurricular activities with a focus on rehab and sports performance for grappling athletes.
Dalton also started and runs the instagram handle @physicaltherapyresearch; where he summarizes physical therapy-based research articles to help himself and others learn and stay up-to-date on recent research, and ultimately bridge the delay between research and clinical practice.
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