What We Know About Blood Flow Restriction Training
‘Blood flow restriction’ is a term that physios have become more and more aware of over the last decade, and for legitimate reasons. There are well over a thousand research papers investigating the safety and efficacy of blood flow restriction training (BFRT) within the realm of physical rehabilitation and sports performance. There are some who expect BFRT to supplement how we regularly treat certain musculoskeletal conditions, and change post-op rehabilitation protocols. There are others who still question this method, or have never been exposed to it. The goal of this article is to shed light on what BFRT is, different ways to apply BFRT, and most importantly how to use it safely.
BFRT, pioneered by Yoshiaki Sato as Kaatsu training, is the brief and intermittent occlusion of arterial and venous blood flow using a tourniquet while at rest or exercising. Using this technique, you can exercise using significantly less weight (20-30% 1RM) and still achieve significant gains in muscle size and strength.1, 2 BFRT has opened up a window of opportunity to better mitigate the negative effects of injury and surgery during specific rehab phases.
The Current Physio Dilemma: Atrophy
As a physio, it can be extremely challenging to battle one major negative consequence of injury and/or surgery àmuscle atrophy. This is especially true when patients simply cannot tolerate the demands necessary to stimulate muscle growth. This may be secondary to pain, tissue capacity being low, weight-bearing/load precautions, or simply the fact that a person cannot tolerate the effort/fatigue associated with moderate to high exercise intensities. If only there was a way to adequately challenge patients safely with submaximal loads…
A Viable Solution: BFRT
What we know from muscle growth physiology is that we either need to induce enough mechanical OR metabolic stimuli in order to stimulate muscle hypertrophy.3 Think of mechanical stimuli as the external load, thus lifting a heavy weight would increase mechanical tension compared to a light weight. Think of metabolic stimuli as how hard the muscle is working, thus sprinting would increase metabolic stress compared to walking. There is evidence to suggest it typically takes at least 12-16 weeks working at 60-80% 1RM to induce muscle hypertrophy.4 However, muscle hypertrophy can also be attained if working at lower loads (30-50% of 1RM) until failure. It is the relationship between mechanical and metabolic stimuli that can explain this – metabolic stress can make up for low mechanical tension to still induce positive muscle gains.
How does BFRT fit into this equation? Although the mechanisms are not fully understood and we are not certain of the chronological order, we do know BFRT performed at the right dose leads to muscle size and strength gains. Simply putting a tourniquet on a limb and occluding a percentage of arterial inflow and venous outflow induces metabolic stress. Performing BFRT with an appropriate device, which we will get to later, creates an anaerobic environment in the limb due to decreased oxygen supply. When BFRT is performed with low-level exercise, or even at rest, it signals local and systemic adaptations that are beneficial to the musculoskeletal system.
What Are The Different Applications of BFRT?
It is important to note that BFRT does not change anything that we do as physios, it only augments our desired patient outcomes. This is one of the first statements I make about BFRT when introducing it to someone, especially a physio! Our goal is to help people recover from an injury or surgery, move better, perform better, and leave them at a higher capacity. That will never change. HOWEVER, how we get to those desired outcomes and the amount of time it takes can be affected by BFRT. This is especially true when some of our patients can only tolerate very low loads and intensities that we know are not challenging them enough.
What’s amazing about this technique is that it can be beneficial throughout the continuum of care. Whether you use it prior to surgery, immediately after surgery or an injury, during the phases of rehab, and even in the realm of performance and recovery – BFRT can help! There is evidence to support that performing BFRT with low-load resistance training (20-50% 1RM) can lead to gains in muscle size and strength.1, 5 Evidence also suggests BFRT can improve bone health,5improve cardiovascular health including VO2 max,6and can even improve muscle activation, perfusion, and endurance following surgeries such as ACL reconstruction.7
Is BFRT Safe?
Safety first! This technique is not for everyone from a tolerance and safety perspective. All of the early research in BFRT was focused on safety due to the concerns of potential blood clots, muscle damage, blood pressure, etc. So what does the research say?
“The collective literature appears to indicate that a proper prescription of BFRT poses little risk of directly casing a Venous Thromboembolism (VTE).”8
What we have also learned is that tourniquets alone do not pose a risk for clotting. Another study found that tourniquets actually increase levels of tPA antigen (a fibrinolytic enzyme that breaks down clots) immediately after BFRT.9 What the research also suggests is in order to avoid potential tourniquet risks such as nerve tissue injury, skin breakdown, and pain, BFRT needs to be applied with wider cuffs at lower pressures and for specific durations (no more than 20 minutes).
You can learn more about contraindications for BFRT in the table at the bottom of this article. A quick rule of thumb is as long as the person doesn’t have one of these contraindications and can tolerate high-intensity resistance exercise they can likely tolerate BFRT. However, it is important to educate yourself and get BFRT certified. There are only two FDA listed BFRT medical devices on the market that further ensure safety (Smart Cuffs and the Delfi unit). We recommend only performing BFRT with either one of these units as it allows for personalized BFRT. Personalized BFRT is made possible when something called limb occlusion pressure (LOP) is measured. This is the minimal pressure needed to sufficiently occlude the deep arteries and superficial veins. LOP can vary for every individual, even side-to-side. It is imperative that we are performing BFRT at specific percentages of LOP (up to 50% upper extremity, 80% lower extremity) to get the gains seen in the research. This is only possible with BFR tourniquets that are designed to occlude percentages of the arteries and veins.
BFRT is not for everyone, however it is a technique that is quickly gaining popularity in the rehabilitation world. It is important that all physios stay updated on new techniques so that they can educate their patients if questioned. More importantly, if there is a safe technique backed by research that can augment better patient outcomes, it is something we should be providing to our patients when appropriate.
- Slysz J, Stultz J, Burr JF. The efficacy of blood flow restricted exercise: a systematic review and meta-analysis. J Sci Med Sport. 2016;19(8):669–75. doi: 10.1016/j.jsams.2015.09.005.
- Le Cara, E., PhD, MBA, ATC, CSCS, Novo, M., PT, DPT, Rolnick, N., Pt, DPT, MS, & Ascanio, Y., PT, DPT. (n.d.). Blood Flow Restriction Level 1(Vol. 1). Smart Tools.
- Ozaki H, Loenneke JP, Buckner SL, et al. Muscle growth across a variety of exercise modalities and intensities: contributions of mechanical and metabolic stimuli. Med Hypotheses. 2016;88:22–6.
- Garber CE, et al. American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Med Sci Sports Exerc.2011 Jul;43(7):1334-59. doi: 10.1249/MSS.0b013e318213fefb.
- Hughes L, Paton B, Rosenblatt B, et al. Blood flow restriction training in clinical musculoskeletal rehabilitation: a systematic review and meta-analysis. Br J Sports Med 2017:bjsports-2016-097071
- Ozaki H, Sakamaki M, Yasuda T, et al. Increases in thigh muscle volume and strength by walk training with leg blood flow reduction in older participants. J Gerontol 56 2011b;66:275–263.
- Žargi T,Drobnič M, Stražar K, Kacin A.Short-Term Preconditioning With Blood Flow Restricted Exercise Preserves Quadriceps Muscle Endurance in Patients After Anterior Cruciate Ligament Reconstruction. Front Physiol. 2018 Aug 24;9:1150. doi: 10.3389/fphys.2018.01150
- Bond CW, Hackney KJ, Brown SL, Noonan BC. Blood Flow Restriction Resistance Exercise as a Rehabilitation Modality Following Orthopaedic Surgery: A Review of Venous Thromboembolism Risk. J Orthop Sports Phys Ther.2019 Jan;49(1):17-27. doi: 10.2519/jospt.2019.8375
- Clark BC, Manini TM, Hoffman RL, Williams PS, Guiler MK, Knutson MJ, McGlynn ML, Kushnick MR (2010) Relative safety of 4 weeks of blood flow-restricted resistance exercise in young, healthy adults. Scand J Med Sci Sports. doi: 10.1111/j.1600-0838.2010.01100