Blood Flow Restriction Training
What is it?
Blood flow restriction (BFR) training is a method used to increase muscle mass and strength, without requiring a large mechanical load. A pressurized cuff is placed around the active limb proximal to the working muscle to restrict blood flow. You have probably seen crude versions of this technique, where makeshift tourniquets are haphazardously applied to either arm or leg. While this effort may appear to do the trick, it gives a poor estimate of blood occlusion and can be dangerous.
If available, it is recommended to use a designated blood flow restriction device, as they automatically adjust cuff pressure to the appropriate amount and are much safer. Blood flow restriction training offers potential benefits to those with load bearing limitations such as post-operation patients, the elderly, or anyone with limited gym access. The objective of this blog post is to better understand the method of blood flow restriction and how it can be useful to you.
The Biochemical (brief) Deep Dive
The scientific literature1 2 comparing BFR and heavy load training, has found comparable results in outcome regarding muscle size and strength. This is shocking and makes BFR feel like a physiological cheat code. My intention is to provide a reasonably coherent summary, of the current biochemical processes, thought to be driving the success of blood flow restriction training. Under traditional resistance exercise muscle growth occurs through a process termed mechanotransduction 3, where mechanical stress is converted into a chemical signal in the muscle cell. Certain proteins allow the tension placed on the muscle cell to be sent to the cell's nucleus, where new muscle proteins are coded for production.
However, it is argued that BFR training, independent of mechanical load, cannot access the same metabolic pathway. It is postulated that BFR training uses an alternative pathway for muscle growth related to the accumulation of chemicals released during the training, triggering the physiological response. Lactate, one of these chemicals, has been shown to recruit muscle activation and subsequently growth. Through the accumulation of lactate and many other chemicals, low load BFR seems to hold its key through its ability to fatigue lower threshold motor units that are usually skipped over during heavy load resistance training.
Pouring Through the Literature: The Systematic Review
A systematic review consolidates relevant research to a specific question, distilling many studies' findings into a comprehensive paper, looking at any large-scale trends or patterns. Because of their extensiveness, if done well, systematic reviews are regarded as highly reliable sources. A systematic review 4 published in one of the world's top physiology journals, Frontiers in physiology, measured the recuperation of physical function, rather than the usual metric of muscle mass and strength outcomes, using blood flow restriction therapy. Some of the more clinically relevant daily living tasks measured in these studies included performance on the sit-to-stand test, timed up and go test, and variations of walking tests. The study poured through 4,563 articles, finding only 12 studies that passed their inclusion criteria.
All individuals tested had physical deficiencies deeming heavy resistance training unwise, making them good candidates for BFR training. The BFR intervention spanned from 6 to 12 weeks, testing older adults and patients in need of musculoskeletal rehabilitation. The BFR occlusion range was between 20-30% of their one repetition max (1RM) and most studies used around 75 repetitions per session. The review found that the 30 second sit to stand (30STS) test and the timed up and go (TUG) test, being two prominent measures of physical function required for daily living, both greatly improved.
The 30STS test improved with BFR interventions in four of the six included studies. Furthermore, the TUG test improved with BFR interventions in seven of the eight included studies. Following BFR intervention, improvements were seen in the 30STS and TUG tests in four of six studies and seven of the eight studies respectively. This systematic review has documented compelling evidence supporting the use and benefits of blood flow resistance training in populations aimed towards improving physical functions with everyday tasks.
Can BFR be useful for ACL Rehabilitation?
An article 5 published in Sports Medicine, in 2019, researched the effectiveness of blood flow restriction resistance training in post-surgery anterior cruciate ligament reconstruction (ACLR) patients. One of the difficulties with ACL rehab is the considerable risk of re-injury, of which the large mechanical stress from heavy load resistance training may impose. This introduces BFR resistance training as a potential suitor to those pursuing a full recovery, without adopting the risk from heavy load resistance training (HL-RT). In this study 24 patients completed 8 weeks of biweekly leg press training on both limbs, accompanied by standard hospital rehabilitation. Metrics such as muscle strength, knee joint pain, swelling, and range of motion were collected before and after analysis.
Primarily, this study found that blood flow restriction training and heavy load resistance training yielded similar results in terms of skeletal muscle hypertrophy and strength gains throughout ACL surgery rehabilitation. Furthermore, the blood flow restriction training had a greater reduction in knee joint pain, swelling and a larger increase in range of movement and physical function. This study claims to be the first research comparing blood flow restriction and heavy load resistance training on ACL recovery, it will be interesting to see if these results are replicated going forward.
Farup, J., de Paoli, F., Bjerg, K., Riis, S., Ringgard, S. and Vissing, K. (2015), Fatigue and muscle hypertrophy. Scand J Med Sci Sports, 25: 754-763. https://doi.org/10.1111/sms.12396
Fahs, C.A., Loenneke, J.P., Thiebaud, R.S., Rossow, L.M., Kim, D., Abe, T., Beck, T.W., Feeback, D.L., Bemben, D.A. and Bemben, M.G. (2015), Muscular adaptations to fatiguing exercise with and without blood flow restriction. Clin Physiol Funct Imaging, 35: 167-176. https://doi.org/10.1111/cpf.12141
Dankel SJ, Mattocks KT, Jessee MB, Buckner SL, Mouser JG, Loenneke JP. Do metabolites that are produced during resistance exercise enhance muscle hypertrophy? Eur J Appl Physiol. 2017 Nov;117(11):2125-2135. doi: 10.1007/s00421-017-3690-1. Epub 2017 Aug 3. PMID: 28776271.
Clarkson MJ, May AK, Warmington SA. Chronic Blood Flow Restriction Exercise Improves Objective Physical Function: A Systematic Review. Front Physiol. 2019 Aug 21;10:1058. doi: 10.3389/fphys.2019.01058. PMID: 31496953; PMCID: PMC6712096.
Hughes L, Rosenblatt B, Haddad F, Gissane C, McCarthy D, Clarke T, Ferris G, Dawes J, Paton B, Patterson SD. Comparing the Effectiveness of Blood Flow Restriction and Traditional Heavy Load Resistance Training in the Post-Surgery Rehabilitation of Anterior Cruciate Ligament Reconstruction Patients: A UK National Health Service Randomised Controlled Trial. Sports Med. 2019 Nov;49(11):1787-1805. doi: 10.1007/s40279-019-01137-2. PMID: 31301034.