During my undergraduate studies in sports science, and even now as part of my postgraduate research in the medical field, I continue to encounter blood flow restriction (BFR) as a tool.
“Tool for what?”, you might be wondering.
I intentionally keep that sentence vague because BFR seems to serve multiple purposes, depending on how it’s applied. I have seen it being used in both sports settings to enhance muscle growth and in cardiovascular rehabilitation settings where it can offer a protective effect against injury incurred by ischaemia (loss of blood supply) and reperfusion (regained blood circulation) in events, such as an acute myocardial infarction, otherwise known as a heart attack.
Blood flow restriction is a technique used in exercise and rehabilitation to enhance muscle growth and strength (hypertrophy) by limiting blood flow to specific muscles.
Today, I’d like to explore one of the uses of BFR that you might find beneficial. However, I’ll start with an important disclaimer: always consult a doctor before incorporating BFR into your routine, as it may not be suitable for everyone.
If you’re a gym-goer interested in building muscle mass, you’ve probably come across products like AirBands or similar devices. There are a range of cuffs one can use, from pneumatic, inflatable cuffs with a pressure gauge (like AirBands), to simpler elastic strap-like cuffs that can be tightened around your limbs.
These bands are inflated around your arms or legs to restrict blood flow, resulting in increased muscle hypertrophy (muscle growth).
But how exactly do blood flow restriction bands help us build muscle?
When we inflate a blood pressure cuff around the limb to around 60-80% limb occlusion pressure (the lowest pressure at which blood flow to the limb is restricted), and exercise is performed, it creates a hypoxic environment in the muscle. This lack of oxygen, combined with reduced blood flow, leads to a build-up of metabolites that aren’t cleared away.
This metabolic accumulation forces muscle fibres to work harder with a lower weight (approximately 20% of your 1RM is sufficient), resulting in several changes that stimulate hypertrophy. These mechanisms are explained in detail in Pearson & Houssain’s (2014) review paper, but I’ll briefly go over them here.
What are the mechanisms behind this increased hypertrophy?
One key factor is the increased muscle activation brought about by BFR. This happens primarily through the build-up of metabolites.
An increase in lactate creates an acidic environment and promotes the accumulation of growth hormone, which may contribute to muscle hypertrophy (Loenneke & Pujol, 2009). However, it’s important to note that a localised increase in hormones doesn’t seem to directly cause muscle hypertrophy, as growth appears to occur independently of hormone levels associated with metabolic stress (Pearson & Houssain, 2014). Therefore, the role of these hormones remains unclear.
BFR also causes cell swelling due to metabolite accumulation, resulting in a pressure gradient that enhances blood flow toward the muscle fibres.
The mechanical tension from resistance training also triggers mechanotransduction, a process in which mechanosensors are activated. These sensors convert mechanical energy into chemical signals that regulate muscle build-up and breakdown within cells, shifting the muscle protein balance to stimulate protein synthesis and reduce protein breakdown.
Additionally, mechanical tension – especially during eccentric training – often results in muscle damage due to microtears. As these microtears heal, hypertrophy occurs, leading to muscle growth.
Mechanical load and BFR training can also cause a build-up of reactive oxygen species (ROS), which has been linked to increased muscle cell growth.
BFR seems to increase one particular type of ROS: nitric oxide (NO). NO can stimulate the activation and proliferation of satellite cells (muscle stem cells responsible for muscle regeneration) and mediate protein synthesis.
This ROS build-up may also mediate the proliferation of heat shock proteins (HSPs), which help assemble proteins and neutralise oxidative damage caused by ROS. However, the nature of BFR – specifically factors like heat, ischemia, hypoxia, and acidosis – may also contribute to HSP accumulation, stimulating hypertrophy.
Evidence on this is mixed, with some studies reporting increased HSPs while others do not. This suggests that only certain HSPs may be elevated, and more research is needed to clarify this.
Finally, BFR means that even at lower contraction intensities, more type II muscle fibres (fast-twitch muscle fibres) may be recruited. This could be due to reduced oxygenation of type I muscle fibres and the accumulation of metabolites. The increased recruitment of type II fibres may contribute to a greater hypertrophic effect.
How BFR Increases Hypertrophy, Even at Lower Contraction Intensities
An interesting thing to note is that under BFR conditions, exercise intensity is typically lower. In fact, while hypertrophy generally requires training at 65% of 1RM, BFR allows for muscle adaptations at even 20% of 1RM (Loenneke & Pujol, 2009; Pearson & Houssain, 2014; Scott et al., 2016)! This means that mechanical stress and tension are lower when using BFR.
Normally, it’s usually high mechanical tension and strain that drive muscle hypertrophy during traditional training. In fact, more type II muscle fibers are recruited at higher contraction intensities with higher mechanical tension compared to BFR at lower intensities (Pearson & Houssain, 2014).
So, if mechanical tension is lower with BFR, how does it still promote hypertrophy?
It’s possible that the effects of metabolic stress and mechanical tension are additive. In other words, the combination of slight mechanical tension with high metabolic stress might produce a greater adaptation and promote muscle hypertrophy (Pearson & Houssain, 2014).
Now that we understand the science behind BFR, how can you incorporate it into your own training?
How to Use BFR for Maximum Benefits
To induce BFR effectively, it appears that inflating a 5 cm-wide cuff to around 200 mmHg (between 160-240 mmHg) provides sufficient pressure. If a wider cuff is used, the pressure can be reduced. Conversely, thinner cuffs require higher pressure to achieve the same effect, which could be dangerous and increase the risk of injury. For elastic strap-type cuffs, aim to tighten them to a 6-7 out of 10 on a scale of tightness. The cuff should be strapped around the upper limbs (upper arms and thighs).
For significant benefits, complete 3-5 sets of 15-30 reps or until failure, using approximately 20% of your 1RM, with 30-45 seconds of rest between sets (Scott et al., 2016).
The duration of BFR training can vary from acute to chronic. While some studies have employed twice-daily training for one to two weeks, others have taken a more gradual approach, with 2-4 sessions per week over 3-8 weeks. Some studies inflate the cuff at the start of the session and keep it inflated until the session ends, while others use intermittent hypoxia, deflating the cuff between sets to allow metabolite clearance, although the intermittent method is less commonly used (Scott et al., 2016).
Scott et al. (2016) also report that increased hypertrophy can occur when BFR is combined with moderate- and high-intensity exercise (i.e. at higher percentages of your 1RM).
In some cases, low-load BFR training has been combined with standard high-load training to achieve greater hypertrophic benefits. Combining BFR with other training modalities may be especially useful if you’re looking to train your entire body, as it’s not possible to apply BFR to trunk muscles. Therefore, BFR could be a good add-on during accessory exercises rather than for one’s main lifts. Good exercises to use BFR with include squats, leg presses, bicep curls, and leg extensions.
That’s a lot of information, so here’s a step-by-step guide to help you implement BFR into your own training:
Step-by-Step Guide to Using BFR
- Apply a 5-10 cm-wide cuff around your upper limbs (arms or thighs).
- Inflate the cuff to approximately 200 mmHg (adjust based on cuff size).
- Perform 3-5 sets of 15-30 repetitions, with 30-45 seconds of rest between sets.
- Use 20% of your 1RM for the exercise (about 20% of the weight you can lift for 1 rep max).
- Start with 2-4 sessions per week and adjust as needed.
With the wide range of training protocols used in the literature, how will you know if your BFR training is successful?
As you can see, there is no single “perfect” way to implement BFR. Ultimately, you’ll need to assess whether the stimulus you’re providing is enough to elicit an increased hypertrophic response.
Can BFR actually help you?
What seems evident is that is that BFR can provide hypertrophic benefits for elite athletes, sedentary individuals, the so-called “man on the street”, and even astronauts in space! Its effects have also been observed in elderly populations. In older adults, using BFR during low-load training and walking has been shown to significantly improve muscle strength and size (Centner et al., 2018).
Research suggests that BFR may work particularly well for individuals who struggle to lift heavy weights due to injury, age, or strength limitations. Since BFR uses low loads, it reduces mechanical stress on bones and joints, making it a valuable tool for those with such restrictions (Centner et al., 2018).
BFR is also an excellent option for maintaining training during an injury, as it requires lower loads to achieve adaptation. Additionally, athletes recovering from injury can use BFR to reduce stress on joints while preserving and maintaining muscle mass.
Moreover, athletes may incorporate BFR into their training regimen to stimulate muscle hypertrophy while minimizing muscle damage (Scott et al., 2016). This reduces recovery time after BFR sessions, which is crucial for elite athletes on a strict training programme.
Are There Any Risks Associated with Using BFR?
While BFR can be incredibly effective for muscle growth, it’s crucial to take precautions to avoid potential risks, especially if you have pre-existing health conditions.
The process of limiting blood flow to and from a limb is what allows these hypertrophic adaptations to occur with low training loads. However, the very nature of blood flow restriction can carry risks if not applied properly.
The truth is, there isn’t enough research on the adverse effects of BFR, and many studies do not report any at all. The question then arises: is this because no adverse events occur, or because they haven’t been reported?
What is currently recommended is that you should avoid BFR if you have the following conditions (AIS):
- Peripheral vascular disease
- Previous vascular surgery on the affected limb
- An arteriovenous fistula (an irregular connection between an artery and a vein) in the affected limb
Additionally, if you have any of the following conditions, you should consult a doctor before trying BFR (AIS):
- Cardiovascular disease
- Hypertension
- Venous thromboembolism (including deep vein thrombosis or pulmonary embolism)
- Sickle cell disease
- Hemophilia or other bleeding and clotting disorders
- Previous stroke
- Peripheral neuropathy
If you do not have any of these conditions and decide to try BFR, you should still exercise caution. Avoid over-restriction, as excessive pressure can lead to tissue damage, nerve compression, or blood clot risks. Other potential side effects include rhabdomyolysis (rapid breakdown of damaged muscle), dizziness, and fainting, particularly if you’re unaccustomed to this type of training or use improper techniques.
Should You Stay Away from BFR then?
I don’t mention these risks to deter you from trying BFR. In fact, it can be incredibly safe and effective for many people. Its ability to increase muscle mass, especially in untrained individuals and the elderly, even by lifting lower loads, can be life-changing for those who struggle with physical activity.
Perhaps you have limited mobility or suffer from osteoarthritis and can’t do heavy, weight-bearing exercises without pain. Or maybe you’re older and are at risk of developing sarcopenia due to low muscle size, quality, and function. BFR can be an excellent way to increase muscle mass and size, improve muscle function, and ultimately enhance your quality of life.
However, if you have pre-existing conditions or are unsure whether it’s right for you, it’s best to consult a physician before starting. The benefits of BFR can be immense, but only if it’s safe for you to train in this way.
Conclusion
Blood flow restriction training can be a valuable addition to your workout regimen to promote hypertrophy. It’s especially beneficial for those who find lifting heavy loads challenging. While it does come with some risks, it is safe for most people and could be a great way to switch up your training, so consider giving it a try! As always, please consult with a medical professional before trying any new training methods to ensure they’re safe for you.
Let me know in the comments if you’ve tried BFR training or if you have any questions, and stay tuned for next week’s post!
References
Australian Sports Commission. (2021, February). Blood flow restriction training guidelines. Australian Institute of Sport. https://www.ais.gov.au/position_statements/best_practice_content/blood-flow-restriction-training-guidelines
Centner, C., Wiegel, P., Gollhofer, A., & König, D. (2018). Effects of Blood Flow Restriction Training on Muscular Strength and Hypertrophy in Older Individuals: A Systematic Review and Meta-Analysis. Sports Medicine, 49(1), 95–108. https://doi.org/10.1007/s40279-018-0994-1
Loenneke, J. P., & Pujol, T. J. (2009). The Use of Occlusion Training to Produce Muscle Hypertrophy. Strength and Conditioning Journal, 31(3), 77–84. https://doi.org/10.1519/ssc.0b013e3181a5a352
Pearson, S. J., & Hussain, S. R. (2014). A Review on the Mechanisms of Blood-Flow Restriction Resistance Training-Induced Muscle Hypertrophy. Sports Medicine, 45(2), 187–200. https://doi.org/10.1007/s40279-014-0264-9
Scott, B. R., Loenneke, J. P., Slattery, K. M., & Dascombe, B. J. (2016). Blood flow restricted exercise for athletes: A review of available evidence. Journal of Science and Medicine in Sport, 19(5), 360–367. https://doi.org/10.1016/j.jsams.2015.04.014