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== Introduction ==
== Introduction ==
Muscle weakness is a common occurrence in clinical musculoskeletal conditions worldwide. To improve muscular strength and hypertrophy the American College of Sports Medicine recommends moderate to high load resistance training. The use of moderate to high loads is often not feasible in clinical populations. Furthermore, a number of disease states result in frailty including HIV/AIDS, cancer, sepsis, COPD, and diabetes. This frailty is largely due to the loss of muscle mass. Treatments that prevent muscle wasting or stimulate muscle growth would improve the quality of countless lives<ref>Hamilton, David & MacKenzie, Matthew & Baar, Keith. (2009). Molecular mechanisms of skeletal muscle hypertrophy Using molecular biology to understand muscle growth. Accessed from<nowiki/>https://www.researchgate.net/publication/235702201_Using_molecular_biology_to_understand_muscle_growth/stats</ref>.  Therefore, the emergence of blood flow restriction (BFR) therapy with low intensity training as a rehabilitation tool for clinical populations is becoming popular<ref name=":3">VanWye WR, Weatherholt AM, Mikesky AE. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5609669/ Blood flow restriction training: Implementation into clinical practice.] International journal of exercise science. 2017;10(5):649.</ref>. Training with low loads in combination with venous blood flow occlusion from the working muscle and arterial blood flow restriction to the working muscle (BFR) may be beneficial for such populations<ref>Loenneke JP, Fahs CA, Rossow LM, Sherk VD, Thiebaud RS, Abe T, Bemben DA, Bemben MG. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4133131/ Effects of cuff width on arterial occlusion: implications for blood flow restricted exercise]. European journal of applied physiology. 2012 Aug 1;112(8):2903-12.</ref>.  
[[Muscle]] weakness commonly occurs in a variety of conditions and pathologies. High load [[Strength Training|resistance training]] has been shown to be the most successful means in improving muscular strength and obtaining muscle hypertrophy. However, in certain populations that require muscle strengthening, eg individuals with [[Chronic Pain|chronic pain]] or post-operative patients, high load and high intensity exercises may not be clinically appropriate. Conditions that result in loss of muscle mass such as [[Oncology|cancer]], [[Human Immunodeficiency Virus (HIV)]], [[diabetes]] and [[COPD (Chronic Obstructive Pulmonary Disease)|COPD]] could potentially benefit from muscle strengthening and muscle hypertrophy but cannot tolerate high intensity/ loaded exercises.<ref>Hamilton, David & MacKenzie, Matthew & Baar, Keith. (2009). Molecular mechanisms of skeletal muscle hypertrophy Using molecular biology to understand muscle growth. Accessed from https://www.researchgate.net/publication/235702201_Using_molecular_biology_to_understand_muscle_growth/stats</ref><ref>Miller BC, Tirko AW, Shipe JM, Sumeriski OR, Moran K. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8329318/ The systemic effects of blood flow restriction training: a systematic review]. Int J Sports Phys Ther. 2021 Aug 2;16(4):978-90. </ref><ref>Wooten SV, Fleming RYD, Wolf JS Jr, Stray-Gundersen S, Bartholomew JB, Mendoza D, et al. [https://www.sciencedirect.com/science/article/abs/pii/S0748798321005333 Prehabilitation program composed of blood flow restriction training and sports nutrition improves physical functions in abdominal cancer patients awaiting surgery]. Eur J Surg Oncol. 2021 Nov;47(11):2952-8. </ref><ref>Alves TC, Pugliesi Abdalla P, Bohn L, Da Silva LSL, Dos Santos AP, et al. [https://www.nature.com/articles/s41598-022-19857-3 Acute and chronic cardiometabolic responses induced by resistance training with blood flow restriction in HIV patients]. Sci Rep. 2022 Oct 10;12(1):16989.</ref><ref>Jones MT, Aguiar EJ, Winchester LJ. [https://www.mdpi.com/2673-4540/2/4/16/htm Proposed mechanisms of blood flow restriction exercise for the improvement of type 1 diabetes pathologies]. ''Diabetology''. 2021; 2(4):176-89.</ref><ref>Pitsillides A, Stasinopoulos D, Mamais I. [https://www.sciencedirect.com/science/article/abs/pii/S1360859221000899 Blood flow restriction training in patients with knee osteoarthritis: Systematic review of randomized controlled trials]. J Bodyw Mov Ther. 2021 Jul;27:477-86. </ref>


== Blood flow restriction (BFR) training ==
'''Blood Flow Restriction (BFR) training''' is a technique that combines low intensity exercise with [[blood]] flow occlusion that produces similar results to high intensity training. It has been used in the gym setting for some time but it is gaining popularity in clinical settings.<ref name=":3">VanWye WR, Weatherholt AM, Mikesky AE. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5609669/ Blood flow restriction training: Implementation into clinical practice.] International journal of exercise science. 2017;10(5):649.</ref><ref>Loenneke JP, Fahs CA, Rossow LM, Sherk VD, Thiebaud RS, Abe T, Bemben DA, Bemben MG. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4133131/ Effects of cuff width on arterial occlusion: implications for blood flow restricted exercise]. European journal of applied physiology. 2012 Aug 1;112(8):2903-12.</ref>    
Blood flow restriction training was originally conceived and developed in Japan in the late 1960’s by Yoshiaki Sato and termed KAATSU training<ref name=":5">Accessed from<nowiki/>https://www.sportsmed.org/AOSSMIMIS/members/downloads/SMU/2017Spring.pdf</ref>. Blood flow restriction (BFR) as a modification to traditional exercise modalities, such as resistance training or walking, has become an area of research interest. This technique utilises the application of a pneumatic cuff, similar to a blood pressure cuff, on the proximal aspect of an upper (i.e. distal to the deltoid muscle) or lower extremity (i.e. inguinal crease). A selected pressure is used to provide partial arterial and complete venous occlusion to the distal aspect of the limb. The patient then performs resistance exercises at relatively ''low intensities'' (i.e., 20–30% of 1 repetition maximum [1RM]), ''high repetitions per set'' (i.e., 15–30), and ''short rest intervals between sets'' (i.e., 30 seconds). Research has commonly examined single joint exercises (e.g., plantar flexion, elbow flexion, leg extension) to minimize the complexity of the movement pattern with the blood flow partially restricted<ref name=":4">Pope ZK, Willardson JM, Schoenfeld BJ. [https://journals.lww.com/nsca-jscr/fulltext/2013/10000/Exercise_and_Blood_Flow_Restriction.37.aspx Exercise and blood flow restriction.] The Journal of Strength & Conditioning Research. 2013 Oct 1;27(10):2914-26.</ref>.


== BFR and Strength training ==
== Blood Flow Restriction (BFR) Training ==
BFR training was initially developed in the 1960s in Japan and known as '''KAATSU training'''.<ref name=":5">Accessed from<nowiki/>https://www.sportsmed.org/AOSSMIMIS/members/downloads/SMU/2017Spring.pdf</ref> It involves the application of a pneumatic cuff (tourniquet) proximally to the muscle that is being trained. It can be applied to either the upper or lower limb. The cuff is then inflated to a specific pressure with the aim of obtaining partial arterial and complete venous occlusion. The patient is then asked to perform [[Strength Training|resistance exercises]] at a low intensity of '''20-30% of 1 repetition max''' (1RM), with high repetitions per set (15-30) and short rest intervals between sets (30 seconds) <ref name=":4">Pope ZK, Willardson JM, Schoenfeld BJ. [https://journals.lww.com/nsca-jscr/fulltext/2013/10000/Exercise_and_Blood_Flow_Restriction.37.aspx Exercise and blood flow restriction.] The Journal of Strength & Conditioning Research. 2013 Oct 1;27(10):2914-26.</ref>


=== Understanding the physiology of Muscle Hypertrophy. ===
== BFR and Strength Training ==
Muscle hypertrophy is characterised by an increase in diameter and in total protein content of fibres. It occurs as a result of an enhanced rate of protein synthesis. Muscle atrophy is induced by a decrease in activity and load. Catabolic loss of muscle mass is a decrease in the size of pre-existing muscle fibers, resulting from a dramatic increase in protein degradation and turnover<ref name=":1" />. A strong relationship exists between the cross-sectional area of the muscle and its strength. The greater the cross-sectional area of the muscle  the greater the strength of that muscle. The two primary factors which are important for muscle hypertrophy are <u>mechanical tension</u> and <u>metabolic stress</u>. And when both are combined an environment for muscle hypertrophy is created. Both are necessary to get the effects.  


'''1. Mechanical tension''': Growth and repair of adult skeletal muscle requires the action of a population of normally quiescent myogenic precursors called satellite cells.<ref name=":1">Bonnieu A, Carnac G, Vernus B. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2647158/ Myostatin in the pathophysiology of skeletal muscle]. Current genomics. 2007 Nov 1;8(7):415-22.</ref> These reside between the basal lamina and the plasma membrane of the myofibres.  In response to muscle injury or increased muscle tension, these cells become activated, start proliferating, and are responsible for the repair of damaged muscle fibres as well as the growth of muscle fibres. This sets up a building block for greater muscle hypertrophy and increased cross-sectional area. According to the American College of Sports Medicine (ACSM), optimising muscular strength and hypertrophy can be achieved through moderate to high intensities of resistance exercises. A sufficient load must be placed in the muscle to induce adaptive changes. The target muscles must be subjected to substantially increased load. The ACSM recommends that the load should exceed 70% of the one repetition maximum to achieve maximum hypertrophy.<ref name=":2">Johnny Owens. Owens Recovery Science. Blood Flow Restriction Rehabilitation Accessed from www.owensrecoveryscience.com</ref> 
=== Understanding the Physiology of Muscle Hypertrophy ===
Muscle hypertrophy is the increase in diameter of the muscle as well as an increase of the [[Muscle Proteins|protein]] content within the [[Muscle Fibre Types|fibres]]. An increase in cross-sectional area of the muscle directly correlates with an increase in [[Muscle Strength Testing|strength]]. <ref name=":1">Bonnieu A, Carnac G, Vernus B. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2647158/ Myostatin in the pathophysiology of skeletal muscle]. Current genomics. 2007 Nov 1;8(7):415-22.</ref>


'''2. Metabolic Stress:''' Additionally, under appropriate mechanical loading stress, anabolic hormone concentration levels elevate. The combination of myogenic stem cell activation and anabolic hormone elevation results in protein metabolism and muscle growth. This sets up an environment for muscle hypertrophy. Researchers have suggested that metabolic stress has an important impact on <u>hormonal release</u>, <u>hypoxia</u>, <u>cell swelling</u> and <u>production of reactive oxygen species (ROS).</u> All of these components can initiate anabolic signalling for muscle growth and adaptations on energy metabolism.<ref name=":0">de Freitas MC, Gerosa-Neto J, Zanchi NE, Lira FS, Rossi FE. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5489423/#B11 Role of metabolic stress for enhancing muscle adaptations: practical applications.] World journal of methodology. 2017 Jun 26;7(2):46.</ref> 
'''Muscle tension''' and '''metabolic stress''' are the two primary factors responsible for muscle hypertrophy. 
* During resistance training, muscle contractions compress blood vessels in active muscles, and this occlusion can lead to a reduction of oxygen levels and, consequently, result in a hypoxic environment. <u>Intramuscular hypoxia during exercise can increase the necessity of anaerobic lactic metabolism</u> by activation of hypoxia-inducible factor (HIF-1α) that regulates the expression of glycolytic enzymes. Thus, an exercise that produces high levels of lactate can be associated with hypoxia<ref name=":0" />.


* Scientific evidence shows that <u>load, number of repetitions, and reset between intervals are important factors to induce metabolite accumulation.</u> Gonzalez et al found that acute resistance training with moderate repetitions combined with short rest intervals (70% 1RM, 10-12 repetitions and one minute rest interval) shows an increase in blood lactate, serum concentration of lactate dehydrogenase, growth hormone and cortisol as compared to higher loads, low repetitions combined with longer rest intervals (90% 1RM, 3-5 repetitions and three minute rest intervals). Concerning these findings, <u>duration of rest intervals may reflect directly on the magnitude of metabolic stress</u>. In a review study, researchers demonstrated that short interval sets (less than one minute) are essential in increasing blood lactate and growth hormone production, mainly because of insufficient recovery of phosphocreatine and H+ accumulation.
==== Mechanical Tension and Metabolic Stress ====
* Exercise is a potent physiological stimulus for <u>growth hormone secretion.</u> Both aerobic and resistance exercise results in significant, acute increases in growth hormone secretion.<ref>Wideman L, Weltman JY, Hartman ML, Veldhuis JD, Weltman A. [https://www.ncbi.nlm.nih.gov/pubmed/12457419 Growth hormone release during acute and chronic aerobic and resistance exercise.] Sports medicine. 2002 Dec 1;32(15):987-1004.</ref> Accumulation of lactate and hydrogen ions within the muscle results in an augmented growth hormone release. According to Doessing et al, growth hormone plays a direct role in <u>increased collagen synthesis</u> after exercise<ref name=":2" />.
When a muscle is placed under mechanical stress, the concentration of anabolic [[Hormones|hormone]] levels increase. The activation of myogenic stem cells and the elevated anabolic hormones result in protein metabolism and as such muscle hypertrophy can occur. <ref name=":10">Luke O'Brien. [https://members.physio-pedia.com/learn/blood-flow-restriction-therapy/ Blood Flow Restriction Therapy Course]. Plus. 2019</ref><ref name=":2">Johnny Owens. Owens Recovery Science. Blood Flow Restriction Rehabilitation Accessed from https://www.owensrecoveryscience.com/?gclid=EAIaIQobChMIoda_9I6q8AIVxgorCh0YFgd2EAAYASAAEgK3APD_BwE</ref>


* Lifting heavy loads or doing powerful activities such as sprinting, forces our body to <u>switch from slow twitch oxidative fibres to fast twitch anaerobic fibres</u>. Anaerobic metabolism produces very strong contractions and is very short lived and creates subsequent byproducts. The byproduct of this action lactate and hydrogen ions create the subsequent burn you feel in your muscle
Release of hormones, hypoxia and cell swelling occur when a muscle is under metabolic stress.<ref name=":0">de Freitas MC, Gerosa-Neto J, Zanchi NE, Lira FS, Rossi FE. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5489423/#B11 Role of metabolic stress for enhancing muscle adaptations: practical applications.] World journal of methodology. 2017 Jun 26;7(2):46.</ref> These factors are all part of the anabolism of muscle tissue. 
* Additionally, Nishimura et al demonstrated higher effects of muscle hypertrophy when resistance training is performed during hypoxia, possibly because of the strong influence of hormonal release, the recruitment of fast-twitch muscle fibres, ROS production and cell swelling<ref name=":0" />


* Additional traits during muscle hypertrophy during resistance training or high-intensity training are <u>upregulation of insulin-like growth factor and downregulation of myostatin</u>. Myostatin has an inhibitory effect on myogenic stem cells, so decreased myostatin is a key for muscular hypertrophy<ref name=":2" />.
===== Activation of myogenic stem cells =====
[[File:Myogenesis Schematic of satellite cell myogenesis and markers typical of each stage.jpg|thumb|Myogenesis]]
Myogenic stem cells ([[Satellite Cell|satellite cells]]), are found between the basal lamina and plasma membrane of myofibres. They are normally inactive and become activated in response to [[Muscle Injuries|muscle injury]] or increased muscle tension. These cells are responsible for both repair of damaged muscle fibres and also the growth of the fibres themselves<ref name=":1" />.


=== Effects of Blood Flow Restriction on Muscle Strength ===
===== Release of hormones =====
[[File:HGH function.jpg|thumb|HGH function]]
Any exercise, resistance or [[Aerobic Exercise|aerobic,]] brings about a significant increase in [[Growth Hormone|human growth hormone (HGH)]]. Insulin-like growth factor and growth hormone are responsible for increased [[collagen]] synthesis after exercise and aids muscle recovery. Growth hormone itself does not directly cause muscle hypertrophy but it aids muscle recovery and thereby potentially facilitates the muscle strengthening process.<ref>Wideman L, Weltman JY, Hartman ML, Veldhuis JD, Weltman A. [https://www.ncbi.nlm.nih.gov/pubmed/12457419 Growth hormone release during acute and chronic aerobic and resistance exercise.] Sports medicine. 2002 Dec 1;32(15):987-1004.</ref> The accumulation of lactate and hydrogen ions (eg in hypoxic training) further increases the release of growth hormone. <ref name=":2" />


BFR training is designed to take advantage of these normal physiological adjustments/adaptations to exercise. With BFR training, ''high-intensity exercise is'' ''simulated'' by artificially reducing blood flow to active skeletal muscle during periods of low-intensity exercise. Blood flow is decreased mechanically by placing flexible pressurizing cuffs or elastic-bands around the active limb proximal to the exercising muscle. This technique selectively <u>reduces the outflow from the muscle</u>, thereby '''causing pooling of capillary blood of low oxygen tension.''' This markedly enhances the production of protons and lactic acid. The intent of the manoeuver is to mimic the metabolic environment necessary to stimulate muscle growth while concomitantly recruiting muscle fibres possessing the greatest force-generating capacity.  
High intensity training has been shown to down regulate myostatin and thereby provide an environment for muscle hypertrophy to occur.<ref name=":10" /> Myostatin controls and inhibits cell growth in muscle tissue. It needs to be essentially shut down for muscle hypertrophy to occur. 


Loenneke et al. postulated that low-intensity BFR (LI-BFR) results in '''increased water content of the muscle cells.''' This induces a cascade of anabolic intracellular signalling to occur. This postulation is supported in part by Fry et al. who observed <u>greater increases in muscle size (measured by circumference)</u> with ''LI-BFR'' compared with ''low-intensity resistance exercise without BFR''. The authors suggested that this acute swelling might mechanistically explain part of the increase in muscle protein synthesis observed after LI-BFR. According to Haussinger et al., cell swelling shifts protein balance toward anabolism and thus induces hypertrophy<ref>Wilson JM, Lowery RP, Joy JM, Loenneke JP, Naimo MA. [https://journals.lww.com/nsca-jscr/fulltext/2013/11000/Practical_Blood_Flow_Restriction_Training.20.aspx Practical blood flow restriction training increases acute determinants of hypertrophy without increasing indices of muscle damage.] The Journal of Strength & Conditioning Research. 2013 Nov 1;27(11):3068-75.</ref>.
===== Hypoxia =====
Resistance training results in the compression of blood vessels within the muscles being trained. This causes an hypoxic environment due to a reduction in oxygen delivery to the muscle. As a result of the hypoxia hypoxia-inducible factor (HIF-1α) is activated. This leads to an increase in '''anaerobic lactic metabolism''' and the '''production of lactate'''.<ref name=":0" /> 


In addition, BFR ''hastens'' '''the recruitment of fast-twitch muscle fibres'''. As a result, the functional and metabolic adjustments known to occur during high-intensity exercise without BFR are reproduced during low-intensity exercise with BFR<ref name=":6">Spranger MD, Krishnan AC, Levy PD, O'Leary DS, Smith SA. [https://www.physiology.org/doi/full/10.1152/ajpheart.00208.2015?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed Blood flow restriction training and the exercise pressor reflex: a call for concern]. American Journal of Physiology-Heart and Circulatory Physiology. 2015 Sep 4;309(9):H1440-52.</ref>. Research has demonstrated that BFR exercise training resulted in increased muscular strength, hypertrophy, localized endurance, and cardiorespiratory endurance<ref name=":4" />.
===== Cell Swelling =====
When there is blood pooling and an accumulation of metabolites cell swelling occurs. This swelling within the cells causes an anabolic reaction and results in muscle hypertrophy.<ref name=":9">Wilson JM, Lowery RP, Joy JM, Loenneke JP, Naimo MA. [https://journals.lww.com/nsca-jscr/fulltext/2013/11000/Practical_Blood_Flow_Restriction_Training.20.aspx Practical blood flow restriction training increases acute determinants of hypertrophy without increasing indices of muscle damage.] The Journal of Strength & Conditioning Research. 2013 Nov 1;27(11):3068-75.</ref> The cell swelling may actually cause mechanical tension which will then activate the myogenic stem cells as discussed above.


Hypothetically speaking, the potential mechanisms for these adaptations may include<ref name=":4" />
=== Effects of Blood Flow Restriction on Muscle Strength ===
* hypoxia-induced additional or preferential recruitment of fast-twitch (FT) muscle fibres,
* greater duration of metabolic acidosis via the trapping and accumulation of intramuscular protons (H+ ions) and stimulation of metaboreceptors, possibly eliciting an exaggerated acute systemic hormonal response,
* external pressure-induced differences in contractile mechanics and sarcolemmal deformation, resulting in enhanced growth factor expression and intracellular signalling,
* metabolic adaptations to the fast glycolytic system that stem from compromised oxygen delivery,
* production of reactive oxygen species (ROS) that promotes tissue growth,
* gradient-induced reactive hyperemia after removal of the external pressure, which induces intracellular swelling and stretches cytoskeletal structures that may promote tissue growth, and
* activation of myogenic stem cells with subsequent myonuclear fusion with mature muscle fibres.
Relatively short-duration (4–6 wk) low-intensity BFR training has been associated with a consistent, 10–20% relative increase in muscle strength compared with baseline. Differences were noted based on age, sex, and muscle group being studied. Of importance, the increases in muscle strength were generally comparable to high-intensity exercise without BFR, suggesting that similar gains can be achieved with lower loads using Kaatsu techniques.<ref name=":6" />.


Another study <ref>Sousa, Jbc et al. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5377566/ “Effects of strength training with blood flow restriction on torque, muscle activation and local muscular endurance in healthy subjects.”] ''Biology of sport'' vol. 34,1 (2016): 83-90. doi:10.5114/biolsport.2017.63738</ref>aimed to analyse the effects of six weeks of strength training with and without blood flow restriction (BFR), on torque, muscle activation, and local muscular endurance (LME) of the knee extensors. 37 healthy young individuals were divided into ''four groups'': <u>high intensity (HI)</u>, <u>low-intensity with BFR (LI+BFR)</u>, <u>high intensity and low intensity combined + BFR (COMB)</u>, and <u>low intensity (LI)</u>. Torque, muscle activation and local muscle endurance were evaluated before the test and at the 2nd, 4th and 6th weeks after exercise. All groups had increased torque, muscle activation and local muscle endurance (p<0.05) after the intervention, but the effect size and magnitude were greater in the HI, LI+BFR and COMB groups. In conclusion, the groups with BFR (the LI+BFR and COMB) produced magnitudes of muscle activation, torque and muscle endurance similar to those of the HI group.
The aim of BFR training is to '''mimic the effects of high intensity exercise''' by recreating a hypoxic environment using a cuff. The cuff is placed proximally to the muscle being exercise and low intensity exercises can then be performed. Because the outflow of blood is limited using the cuff capillary blood that has a low oxygen content collects and there is an increase in protons and lactic acid, the same physiological adaptations to the muscle (eg release of hormones, hypoxia and cell swelling) will take place during the BFR training and low intensity exercise as would occur with high intensity exercise.<ref name=":9" />
* '''Low intensity BFR training''' results in greater muscle circumference when compared with normal low intensity exercise. (1)
* '''Low intensity BFR (LI-BFR)''' results in an increase in the water content of the muscle cells (cell swelling).<ref name=":9" /> It also speeds up the recruitment of fast-twitch muscle fibres.<ref name=":6">Spranger MD, Krishnan AC, Levy PD, O'Leary DS, Smith SA. [https://www.physiology.org/doi/full/10.1152/ajpheart.00208.2015?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed Blood flow restriction training and the exercise pressor reflex: a call for concern]. American Journal of Physiology-Heart and Circulatory Physiology. 2015 Sep 4;309(9):H1440-52.</ref> It is also hypothesized that once the cuff is removed a hyperemia (excess of blood in the blood vessels) will form and this will cause further cell swelling.<ref name=":4" />
* '''Short duration, low intensity BFR training''' of around 4-6 weeks has been shown to cause a 10-20% increase in muscle strength. These increases were similar to gains obtained as a result of high-intensity exercise without BFR<ref name=":6" />
A study comparing (1) high intensity, (2) low intensity, (3) high and low intensity with BFR and (4) low intensity with BFR. While all 4 exercise regimes produced increases in torque, muscle activations and muscle endurance over a 6 week period - the high intensity (group 1) and BFR (groups 3 and 4) produced the  greatest effect size and were comparable to each other. <ref>Sousa, Jbc et al. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5377566/ “Effects of strength training with blood flow restriction on torque, muscle activation and local muscular endurance in healthy subjects.”] ''Biology of sport'' vol. 34,1 (2016): 83-90. doi:10.5114/biolsport.2017.63738</ref>


== Equipment ==
== Equipment ==
The BFR technique involves applying a tourniquet cuff to a limb. The cuff is manually tightened or pneumatically inflated to a pressure that occludes venous flow yet allows arterial inflow during rehabilitative exercise.<ref name=":3" /> Some clinicians may use rudimentary techniques to achieve occlusion, such as surgical tubing or elastic straps wrapped tightly around the proximal portion of the exercising limb. This method may or may not completely occlude all arterial and venous blood flow, and there is no way of knowing what occlusive pressure the vessels experience. Further, the relatively thin diameter of the tubing or straps may cause highly localized stresses and ineffective transmission of pressure, potentially causing direct damage to the soft tissues and structures underneath the application site. Review of BFR rehabilitation literature<ref name=":8" /> shows that inconsistencies exist in methodology, equipment and in levels of restriction pressure used. Current non-personalized methodologies of setting BFR pressure may occlude rather than restrict blood flow, increasing the risk of injury during rehabilitation. Furthermore, these non-personalized methods of setting pressure do not provide a consistent stimulus within and across patients, reducing the efficacy of the BFR rehabilitation and inhibiting the meaningful comparison of a full range of BFR studies. James A McEwen et al suggest the use of surgical-grade tourniquet technology with automatic Limb Occlusion Pressure (LOP) measurement capability. These are adapted to incorporate and deliver optimal protocols, for safe and effective application of BFR to consistently achieve optimal patient outcomes in rehabilitation<ref name=":8">McEwen JA, Owens JG, Jeyasurya J. [https://link.springer.com/article/10.1007/s40846-018-0397-7#Sec8 Why is it Crucial to Use Personalized Occlusion Pressures in Blood Flow Restriction (BFR) Rehabilitation?.] Journal of Medical and Biological Engineering. 2019 Apr 2;39(2):173-7.</ref>. 


==== BFR cuff width ====
=== BFR Cuff ===
The cuffs developed for BFR are wider than those traditionally used. The most frequently used cuff width is 10 to 12 cm, although cuffs greater than 15 cm may be more desirable.  Additionally, cuffs are now tapered to conform with the natural proximal-to-distal narrowing of the thigh or upper arm and are limb-circumference specific, which allows them to be fitted to various limb circumferences. Together, these advances enhance the transmission of pressure, and may appropriately mitigate complications caused by finely localized stresses from the cuff itself and reduce the pressure required to reach the same level of occlusion achieved with narrower cuffs.<ref name=":7">Bond CW, Hackney KJ, Brown SL, Noonan BC. [https://www.jospt.org/doi/full/10.2519/jospt.2019.8375 Blood Flow Restriction Resistance Exercise as a Rehabilitation Modality Following Orthopaedic Surgery: A Review of Venous Thromboembolism Risk]. journal of orthopaedic & sports physical therapy. 2019 Jan;49(1):17-27.</ref>
BFR requires a '''tourniquet''' to be placed on a limb. The cuff needs to be tightened to a specific pressure that occludes venous flow while still allowing arterial flow whilst exercises are being performed.  


==== BFR cuff material ====
Simple pieces of equipment such as '''surgical tubing or elastic straps''' have been used in gym settings to achieve this result.<ref name=":8">McEwen JA, Owens JG, Jeyasurya J. [https://link.springer.com/article/10.1007/s40846-018-0397-7#Sec8 Why is it Crucial to Use Personalized Occlusion Pressures in Blood Flow Restriction (BFR) Rehabilitation?.] Journal of Medical and Biological Engineering. 2019 Apr 2;39(2):173-7.</ref> These are not advisable as you are unable to monitor the amount of blood flow occlusion. A thin diameter may also cause too much local pressure and result in tissue damage. 
Many of the narrow cuffs used are made of elastic material whereas the wider cuffs are made of nylon. The '''difference in the material''' may result in differences in the ability to restrict blood flow and some of this difference may be due to differences in initial pressure<ref>Loenneke JP, Fahs CA, Rossow LM, Thiebaud RS, Mattocks KT, Abe T, Bemben MG. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3767914/#B8 Blood flow restriction pressure recommendations: a tale of two cuffs.] Frontiers in physiology. 2013 Sep 10;4:249</ref>. The initial pressure is the pressure applied to the limb by the elastic cuffs prior to actual inflation. Research suggests that arterial occlusion pressure was significantly greater when using the elastic cuff as opposed to the nylon cuff. <ref>Buckner SL, Dankel SJ, Counts BR, Jessee MB, Mouser JG, Mattocks KT, Laurentino GC, Abe T, Loenneke JP. [https://www.researchgate.net/publication/303378637_Influence_of_cuff_material_on_blood_flow_restriction_stimulus_in_the_upper_body Influence of cuff material on blood flow restriction stimulus in the upper body.] The Journal of Physiological Sciences. 2017 Jan 1;67(1):207-15.</ref>


==== BFR cuff pressure ====
=== BFR Cuff Width ===
Blood flow restriction cuff pressure prescription methods have included a standard pressure for all patients, such as 180 mmHg; a pressure relative to the patient's systolic blood pressure, such as 1.2- or 1.5-fold greater than systolic blood pressure; or a pressure relative to the patient's thigh circumference. A pressure specific to each individual would be the safest prescription method, because the same pressure may not necessarily occlude the same amount of blood flow for all individuals under the same conditions.<ref name=":7" />
A wide cuff is preferred in the correct application of BFR. 10-12cm cuffs are generally used. A wide cuff of 15cm may be best to allow for even restriction. Modern cuffs are shaped to fit the natural contour of the arm or thigh with a proximal to distal narrowing. There are also specific upper and lower limb cuffs that allow for better fitment.<ref name=":7">Bond CW, Hackney KJ, Brown SL, Noonan BC. [https://www.jospt.org/doi/full/10.2519/jospt.2019.8375 Blood Flow Restriction Resistance Exercise as a Rehabilitation Modality Following Orthopaedic Surgery: A Review of Venous Thromboembolism Risk]. journal of orthopaedic & sports physical therapy. 2019 Jan;49(1):17-27.</ref>  


Devices and procedures specifically designed for BFR have been developed to individualize the pressure for each patient using plethysmography or Doppler ultrasound to detect blood flow. At rest, the cuff pressure is slowly increased until the flow of blood is no longer detected, a term frequently referred to as total limb occlusion pressure (LOP) or arterial occlusion pressure (AOP). A submaximal percentage (eg, 40%–80%) of that pressure is prescribed for the exercise session. This pressure prescription method ensures that patients are not exercising with a pressure that is too high relative to their systolic blood pressure and accounts for the volume and density of soft tissue underneath the cuff. Further, this method allows for appropriate progression of the pressure, similar to the way a clinician would progress resistive load, repetitions performed per set, and total number of sets performed for a resistance exercise.<ref name=":7" />
=== BFR Cuff Material ===
BFR cuffs can be made from either elastic or nylon. The narrower cuffs are normally elastic and the wider nylon. With elastic cuffs there is an initial pressure even before the cuff is inflated and this results in a different ability to restrict blood flow as compared with nylon cuffs.<ref>Loenneke JP, Fahs CA, Rossow LM, Thiebaud RS, Mattocks KT, Abe T, Bemben MG. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3767914/#B8 Blood flow restriction pressure recommendations: a tale of two cuffs.] Frontiers in physiology. 2013 Sep 10;4:249</ref>


The literature suggests that the pressure applied largely depends upon the '''width of the cuff''' applying the stimulus as well as the '''size of the limb''' to which the stimulus is applied. The pressure applied should be high enough to occlude venous return from the muscle but low enough to maintain arterial inflow into the muscle.<ref>Loenneke JP, Thiebaud RS, Abe T, Bemben MG. [https://www.ncbi.nlm.nih.gov/pubmed/24636784 Blood flow restriction pressure recommendations: the hormesis hypothesis.] Medical hypotheses. 2014 May 1;82(5):623-6.</ref> Loenneke JP et al in the study<ref>Loenneke JP, Kim D, Fahs CA, Thiebaud RS, Abe T, Larson RD, Bemben DA, Bemben MG. [https://www.ncbi.nlm.nih.gov/pubmed/25187395 Effects of exercise with and without different degrees of blood flow restriction on torque and muscle activation]. Muscle & nerve. 2015 May;51(5):713-21.</ref> found that an arterial occlusion of  40% to 50% causes increase in muscle activation [66% vs. 87% maximal voluntary contraction (30% 1RM)]  but no further increase in strength was seen with a higher pressure. It would, therefore, appear that a pressure level that results in 40% to 50% arterial occlusion is optimal. However, Wilson et al. (2013) found that in practical blood flow restriction (where wraps are used to apply pressure), a perceived ''wrap tightness of 7 out of 10 results in complete venous'', but not arterial, occlusion. This is consistent with the stated aim of blood flow restriction training to maintain arterial inflow while occluding venous return during exercise. Furthermore, this level of perceived wrap tightness has also been used by Lowery et al. (2014) in an investigation demonstrating the efficacy of blood flow restriction training in eliciting hypertrophy<ref>Accessed from  https://www.strengthandconditioningresearch.com/blood-flow-restriction-training-bfr/#5 on 16/04/19</ref><ref>Lowery RP, Joy JM, Loenneke JP, de Souza EO, Machado M, Dudeck JE, Wilson JM. [https://www.ncbi.nlm.nih.gov/pubmed/24188499 Practical blood flow restriction training increases muscle hypertrophy during a periodized resistance training programme]. Clinical physiology and functional imaging. 2014 Jul;34(4):317-21.</ref>.
Elastic cuffs have been shown to provide a significantly greater arterial occlusion pressure as opposed to nylon cuffs. <ref>Buckner SL, Dankel SJ, Counts BR, Jessee MB, Mouser JG, Mattocks KT, Laurentino GC, Abe T, Loenneke JP. [https://www.researchgate.net/publication/303378637_Influence_of_cuff_material_on_blood_flow_restriction_stimulus_in_the_upper_body Influence of cuff material on blood flow restriction stimulus in the upper body.] The Journal of Physiological Sciences. 2017 Jan 1;67(1):207-15.</ref>


== Clinical Application ==
=== BFR Cuff Pressure ===
Available scientific data has reported multiple benefits of low-intensity-Blood Flow Restriction (LI-BFR) in health outcomes and rehabilitation: reduce muscle atrophy, increases in muscular strength and hypertrophy improvements in elderly, vascular function and cardiovascular system. Thus, this training methodology results very useful for a large range of populations from athletes, recreationally training to clinical exercise<ref>PICÓN MM, CHULVI IM, CORTELL JM, Tortosa J, Alkhadar Y, Sanchís J, Laurentino G. [https://www.ncbi.nlm.nih.gov/pubmed/29795722 Acute cardiovascular responses after a single bout of blood flow restriction training.] International Journal of Exercise Science. 2018;11(2):20.</ref>.
Different blood flow restriction cuff pressure prescription methods:<ref name=":7" />
# a standard pressure (used for all patients) for e.g. 180 mmHg;
# a pressure relative to the patient's systolic blood pressure, for e.g. 1.2- or 1.5-fold greater than systolic blood pressure;
# a pressure relative to the patient's thigh circumference.  
It is the safest to use a pressure specific to each individual patient, because different pressures occlude the amount of blood flow for all individuals under the same conditions.<ref name=":7" />


=== Procedure ===
A Doppler ultrasound or plethysmography can be used to determine the blood flow to the limb. The cuff is inflated to a specific pressure where the arterial blood flow is completely occluded. This known as limb occlusion pressure (LOP) or arterial occlusion pressure (AOP). The cuff pressure is then calculated as a percentage of the LOP, normally between 40%-80%. 
The tourniquet is placed on the proximal arm for upper limb and proximal thigh for the lower limb. Inflate the cuff to an appropriate level of safety and effectiveness. For lower extremity,  the cuff is inflated to restrict 80% of the arterial blood flow and 100% of the venous blood flow and for the upper extremity, the cuff is inflated to restrict 50%of the arterial blood flow and 100% of the venous blood flow. With the cuff in place and appropriate pressure applied, the patient carries out standard upper extremity or lower extremity exercises. The intensity of the exercise is 20-30% of 1 RM in BFR training.


=== Exercise Prescription<ref name=":2" /> ===
Using this method is preferable as it ensures patients are  exercising at the correct pressure for them and the type of cuff being used. It is safer and makes sure that they are exercising at optimal pressures, not too high to cause tissue damage and also not too low to be ineffective.<ref name=":7" />


===== 1. Training Frequency =====
The pressure of the cuff depends upon the width of the cuff as well as the size of the limb on which the cuff is applied. 
In theory, strength training with BFR can be done daily and in some studies, Nielsen et al suggest that it has been done twice a day. Several studies looking at Endurance training and BFR has shown effects with 4 - 6 days of training.  


===== 2. Training Duration =====
The key to BFR is that the pressure needs to be high enough to occlude venous return and allow blood pooling but needs to be low enough to maintain the arterial inflow <ref>Loenneke JP, Kim D, Fahs CA, Thiebaud RS, Abe T, Larson RD, Bemben DA, Bemben MG. [https://www.ncbi.nlm.nih.gov/pubmed/25187395 Effects of exercise with and without different degrees of blood flow restriction on torque and muscle activation]. Muscle & nerve. 2015 May;51(5):713-21.</ref>Perceived wrap tightness, on a scale of 0-10 has also been used to conduct BFR training. Wilson et al (2013) found that a perceived wrap tightness of 7 out of 10 resulted in total venous occlusion but still allowed arterial inflow.  <ref>Accessed from  https://www.strengthandconditioningresearch.com/blood-flow-restriction-training-bfr/#5 on 16/04/19</ref><ref>Lowery RP, Joy JM, Loenneke JP, de Souza EO, Machado M, Dudeck JE, Wilson JM. [https://www.ncbi.nlm.nih.gov/pubmed/24188499 Practical blood flow restriction training increases muscle hypertrophy during a periodized resistance training programme]. Clinical physiology and functional imaging. 2014 Jul;34(4):317-21.</ref>
The effect's size for training duration demonstrates that longer duration up to 10 weeks has the largest effect size. Early hypertrophy is observed with BFR  and this may be from increased satellite fusion and resultant hypertrophy. It is common that the patient notices hypertrophy within the first 2 weeks of BFR training.


===== 3. Rest Periods =====
== Clinical Application ==
The largest effect size is seen with rest periods of 30 seconds. It is important to keep the cuff inflated during the rest periods to capture the metabolites.
BFR has been used in athletes and recreational training to obtain muscle hypertrophy. It can also be used in clinical populations that cannot perform high intensity exercises because of the stage of their condition or pathology involved.<ref>PICÓN MM, CHULVI IM, CORTELL JM, Tortosa J, Alkhadar Y, Sanchís J, Laurentino G. [https://www.ncbi.nlm.nih.gov/pubmed/29795722 Acute cardiovascular responses after a single bout of blood flow restriction training.] International Journal of Exercise Science. 2018;11(2):20.</ref>


===== 4. Tourniquet Cuff Pressure =====
The amount of pressure needed to occlude blood flow in the limb depends on the limb size, underlying soft tissue, cuff width and device used.


===== 5. Limb Occlusion Pressure =====
Examples of BFR training in the clinic:
It is the minimal amount of pressure needed to occlude arterial blood flow. 3rd Generation Tourniquet System features a built-in system to measure vascular flow, which allows personalised tourniquet pressure for each individual patient and eliminates the need to account for cuff width, limb size or blood pressure. A pressure of 80% occlusion for lower extremities and 50% for the upper extremities is recommended.


===== 6. Training Intensity =====
<div class="row">
A load of 15-30% 1RM has the largest size effect. A Higher load may have actually pumping effect to eliminate the metabolites and blunt the response. Lower intensities  such as cycling, walking and isometrics have a lower response than 15-30% load.
  <div class="col-md-4"> {{#ev:youtube|FbXSdCm8Q6U|250}} <div class="text-right"><ref>NovaCare SelectPT TV. The ACL Road to Recovery - Blood Flow Restriction. Available from: https://youtu.be/FbXSdCm8Q6U</ref></div></div>
  <div class="col-md-4">{{#ev:youtube|2fMUpxqJq48|250}} <div class="text-right"><ref>Performance Physical Therapy & Wellness - Blood Flow Restriction Therapy (BFR). Available from: https://youtu.be/2fMUpxqJq48</ref></div></div>
<div class="col-md-4">{{#ev:youtube|pDiLSj6ixTo|250}} <div class="text-right"><ref>Kate Warren. Blood Flow Restriction Training and Physical Therapy | Breaking Athletic Barriers | EVOLVE PT. Available from: https://youtu.be/pDiLSj6ixTo</ref></div></div>
</div>
=== Procedure ===
'''Upper Limb:'''  The tourniquet is placed on the upper arm. The cuff is inflated to restrict 50% of the arterial blood flow and 100% of the venous flow.   


===== 7. Exercise Selection =====
'''Lower limb:''' The tourniquet is placed on the upper thigh. The cuff is inflated to restrict 80% of the arterial blood flow and 100% of the venous flow. With the cuff inflated to the correct pressure normal exercises are performed at about 20-30% of 1RM.  
BFR is typically a single joint exercise modality for strength training or low-level cardio exercise.
* The standard repetition scheme used in BFR is a set of 30 repetitions followed by a 30-second rest followed by 3 more sets of 15 with 30 second rests in between (30/15/15/15). This gives us the target 75 repetitions. The first set of 30 can be seen as the priming load to begin the Cori cycle or the Lactic acid cycle. This first set is typically tolerated well by the patient and they often feel like it is too easy. The tourniquet is left inflated during the rest period, this is very important in order to trap metabolites.  


* The following 3 sets and rest periods will feel very difficult because of the subsequent lactate build up. The RPE is closely related to lactate accumulation. Also, the patients may feel their heart rate raise somewhat during the exercise. This is normal because of the reduced venous return, subsequent decreased stroke volume and increased HR to maintain cardiac output. If at anytime the patient becomes faint, dizzy has moderate to severe pain under the tourniquet cuff or begins to feel numbness or paresthesia in the limb '''stop''' the exercise session.  
=== Exercise Prescription  ===
Exercise prescription for BFR varies, this is dependent on whether it is being applied during resistance training (BFR-RE), aerobic training (BFR-AE) or passively without exercise (P-BFR)<ref name=":12">Patterson SD, Hughes L, Warmington S, Burr J, Scott BR, Owens J, Abe T, Nielsen JL, Libardi CA, Laurentino G, Neto GR. Corrigendum: [https://pdfs.semanticscholar.org/3522/8993adf1ab323d3dd53bb6371ad9beaf43a0.pdf Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety.] Frontiers in physiology. 2019;10.</ref>[[File:BFR1.jpg|thumb|Model of exercise prescription with BFR-RE<ref name=":12" />|500x500px]]
==== BFR-RE (resistance training) ====
[[File:BFR2.jpg|thumb|Model of exercise prescription with BFR-AE<ref name=":12" />|500x500px]]For optimal results, resistance training should ideally be done 2-4 times per week. In theory, strength training with BFR can be done daily, however, this may not be the best long term strategy and training 1-2 times per day should only be done for shorter time periods of 1-3 weeks.  BFR-RE is typically a single joint exercise modality for strength training.<ref name=":12" />


* Once the patient finishes the exercise session the reperfusion of blood into the limb flushes out the lactate and the lactate “burn” in the limb generally goes away relatively quickly. They do often feel very fatigued in the limb and studies measuring force production immediately after BFR even at low loads have demonstrated significantly reduced force. Because of this high intensity exercises such as olympic lifts, plyometrics, agility work should not be done immediately after BFR. These same exercises should also not be done while using BFR. However, there will be times when the patient is unable to hit the target volume. Remember volume is key for strength and hypertrophy in BFR training. 
Muscle hypertrophy can be observed during BFR-RE within a 3 week period but most studies advocate for longer training durations of more than 3 weeks.  
* Exercises: 
Upper extremity: Upper body ergometer, isometrics, scapular rows, serratus punches, shoulder exercises, PNF patterns, bench press, push-up, elbow flexion, elbow extension, elbow supination, elbow pronation, wrist and all hand gripping exercises.


Lower extremity: Walking, cycling, isometrics, leg extension, hamstring curl, straight leg raises, terminal knee extension, hip range of motion exercises, leg press,   squat, lunge, ankle and all Foot Exercises.
A load of 20-40% 1RM has been shown to produce consistent muscle adaptations for BFR-RE. 
* The most commonly used training volume in literature is 75 repetitions across 4 sets (30, 15, 15, 15).
* Rest periods between sets are normally about 30-60 seconds.
* It is important to keep the cuff inflated during the rest periods to capture the metabolites. Intermittent pressure can be applied however this is not as effective as continuous.<ref name=":12" />
[[File:BFR3.jpg|thumb|Model of Exercise Prescription with P-BFR<ref name=":12" />|500x500px]]The amount of pressure needed to occlude blood flow in the limb depends on the limb size, underlying soft tissue, cuff width and device used. The arterial occlusion pressure applied is dependent on whether it is an upper or lower limb and should be between 40%-80%.<ref name=":12" />


===== 8. Exercise Progression =====
==== BFR-AE (aerobic training) ====
Below are guidelines to follow concerning exercise progression and difficulties with volume achievement: Load: 20-30% 1RM (Determined, Estimated). If the patient achieves:
BFR can be applied during aerobic exercise and in research has normally been applied during walking or cycling. It is somewhat more difficult to maintain cuff pressures and literature lacks standardization of cuff pressures during BFR-AE.<ref name=":12" />Also, there is limited evidence that BFR training improves aerobic capacity and performance in trained athletes.<ref>Castilla-López C, Molina-Mula J, Romero-Franco N. [https://www.sciencedirect.com/science/article/pii/S1728869X2200020X?via%3Dihub#sec2 Blood flow restriction during training for improving the aerobic capacity and sport performance of trained athletes: A systematic review and meta-analysis.] Journal of Exercise Science & Fitness. 2022 Mar 22.</ref>


75 Repetitions = Continue with training, re-assess 1RM within 1-3 sessions. Reestablish new 20-30% range as strength improves.  
==== P-BFR (passively without exercise) ====
Passively applied BFR (i.e. BFR is applied and no exercise is performed) has not been widely researched. However, it has shown positive results in reducing muscle atrophy post ACL surgery. The studies conducted did not use standardised pressures and some pressures used were high enough to possibly completely occlude blood flow, which poses safety risks. P-BFR could potentially be beneficial in postoperative patients however more research is needed in this field.<ref name=":12" />


60-74 Repetitions = Continue with training, but extend rest period between sets 3 and 4 to 45 seconds. Until 75 repetitions is completed.
== Side Effects ==
 
Reported side effects while performing BFR exercises are fainting and dizziness, numbness, pain and discomfort, delayed onset muscle soreness<ref>Brandner, Christopher & May, Anthony & Clarkson, Matthew & Warmington, Stuart. (2018). [https://www.researchgate.net/publication/324233071_Reported_Side-effects_and_Safety_Considerations_for_the_Use_of_Blood_Flow_Restriction_During_Exercise_in_Practice_and_Research Reported Side-effects and Safety Considerations for the Use of Blood Flow Restriction During Exercise in Practice and Research.] Techniques in Orthopaedics. 33. 1. 10.1097/BTO.0000000000000259.</ref>.
45-59 Repetitions = Continue with training, but extend rest period between all sets to 45- 60 seconds.
 
<44 Repetitions = Reduce the load by approximately 10% until 75 repetitions are achieved.
 
Forced to stop before 75 repetitions because of undue pain, soreness or general uncomfortable feeling underneath the tourniquet cuff = Reduce tourniquet pressure by 10mmHg at each training session until cuff tolerance is achieved. Ramp cuff pressure back up 10 mmHg to target limb occlusion pressure if patient can tolerate.
 
===== 9. Rehabilitation Guidelines =====
* In the very early phases of rehab after injury or surgery, the goal is to mitigate atrophy and promote a healing environment. During this phase simply performing BFR with low-level exercises such as isometrics with or without electrical-stimulation, mat exercises (SLR/4-way hip) or no exercise can achieve this. For example, researchers in the UK are beginning a study using BFR in the ICU to decrease muscle atrophy.  
 
* Once the patient moves into a more sub-acute stage, BFR can be used for slightly higher loads such as walking and cycling. This has been shown to increase strength, hypertrophy and endurance. As the patient can tolerate additional load, he can move into isotonic exercises with a 15-30% load. This will produce even more substantial gains.  


* As the patient transitions into the later phases of rehab, a typical transition to BFR and HIT training on alternating days can be made. This has demonstrated even larger gains than BFR alone. This also acts as a bridge for the patient to discharge to a home strengthening program consisting of just HIT training.  
== Contraindications ==
All patients should be assessed for the risks and contraindications to tourniquet use before BFR application.
* Patients possibly at risk of adverse reactions are those with poor [[Cardiovascular System|circulatory system]]<nowiki/>, [[obesity]], diabetes, arterial calcification, [[Sickle Cell Anemia|sickle cell]] trait, severe [[hypertension]], or renal compromise<ref>DePhillipo NN, Kennedy MI, Aman ZS, Bernhardson AS, O'Brien L, LaPrade RF. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6203234/ Blood Flow Restriction Therapy After Knee Surgery: Indications, Safety Considerations, and Postoperative Protocol]. Arthroscopy techniques. 2018 Oct 1;7(10):e1037-43.</ref>.
* Potential contraindications to consider are venous thromboembolism, peripheral vascular compromise, sickle cell anemia, extremity infection, lymphadenectomy, cancer or tumor, extremity with dialysis access, acidosis, open fracture, increased intracranial pressure vascular grafts, or medications known to increase clotting risk<ref name=":2" />.


* The initial training with BFR has made permanent anatomical changes through increased myocyte incorporation and thus improving the patient's muscle protein synthesis potential. BFR can also be used as a form of strength and endurance training to supplement the patient while they are working on a higher-level program such as plyometrics, running and agility into the late phases of rehab. In cases of setbacks due to reinjury, BFR is a great modality to start back up during these times to diminish the losses the patient might have during this setback. The patients really appreciate the fact that they are maintaining or increasing their strength while they are recovering instead of meds and RICE while they watch their gains atrophy daily.
== Safety Implications ==
 
Safety implications around BFR are conflicting. Safety concerns are mainly around the formation of venous thromboembolism ([[Deep Vein Thrombosis|deep vein thrombosis]] and [[Pulmonary Embolism|pulmonary embolism]]) and muscle damage.<ref name=":7" /> Different safety concerns and implications are discussed below:
=== Side Effects ===
Reported side effects while performing BFR exercises are fainting and dizziness, numbness, pain and discomfort, delayed onset muscle soreness<ref>Brandner, Christopher & May, Anthony & Clarkson, Matthew & Warmington, Stuart. (2018). [https://www.researchgate.net/publication/324233071_Reported_Side-effects_and_Safety_Considerations_for_the_Use_of_Blood_Flow_Restriction_During_Exercise_in_Practice_and_Research Reported Side-effects and Safety Considerations for the Use of Blood Flow Restriction During Exercise in Practice and Research.] Techniques in Orthopaedics. 33. 1. 10.1097/BTO.0000000000000259.</ref>.


=== Contraindications ===
==== '''Blood hemostasis and BFR''' ====
All patients should be assessed for the risks and contraindications to tourniquet use before BFR application. Patients possibly at risk of adverse reactions are those with poor circulatory systems, obesity, diabetes, arterial calcification, sickle cell trait, severe hypertension, or renal compromise<ref>DePhillipo NN, Kennedy MI, Aman ZS, Bernhardson AS, O'Brien L, LaPrade RF. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6203234/ Blood Flow Restriction Therapy After Knee Surgery: Indications, Safety Considerations, and Postoperative Protocol]. Arthroscopy techniques. 2018 Oct 1;7(10):e1037-43.</ref>. Potential contraindications to consider are venous thromboembolism, peripheral vascular compromise, sickle cell anaemia, extremity infection, lymphadenectomy, cancer or tumor, extremity with dialysis access, acidosis, open fracture, increased intracranial pressure vascular grafts, or medications known to increase clotting risk<ref name=":2" />.
Blood has the ability to clot through various systems of coagulation. Blood coagulation is kept in check in part by the fibrinolytic system. Fibrinolysis can help prevent the progression of a blood clot into a venous thromboembolism.


=== Safety Implication ===
A systematic review conducted by da Cunha Nascimento et al in 2019 examined the long and short term effects on blood hemostasis (the balance between fibrinolysis and coagulation). It concluded that more research needs to be conducted in the field before definitive guidelines can be given.<ref name=":11">da Cunha Nascimento D, Petriz B, da Cunha Oliveira S, Vieira DC, Funghetto SS, Silva AO, Prestes J. [https://www.dovepress.com/effects-of-blood-flow-restriction-exercise-on-hemostasis-a-systematic--peer-reviewed-article-IJGM Effects of blood flow restriction exercise on hemostasis: a systematic review of randomized and non-randomized trials.] International Journal of General Medicine. 2019;12:91.</ref>
# Thrombus Formation
Although speculative, an initial safety concern regarding LL-BFR training included thrombus formation (i.e., blood clot). Research examining LL-BFR training with healthy individuals and older adults with heart disease found no change in blood markers for thrombin generation or intravascular clot formation. Furthermore, data from two surveys of nearly 13,000 individuals utilizing BFR training found that the incidence of deep venous thrombosis was <.06% and pulmonary embolism was <.01%.<ref name=":3" />  The systematic review<ref>da Cunha Nascimento D, Petriz B, da Cunha Oliveira S, Vieira DC, Funghetto SS, Silva AO, Prestes J. [https://www.dovepress.com/effects-of-blood-flow-restriction-exercise-on-hemostasis-a-systematic--peer-reviewed-article-IJGM Effects of blood flow restriction exercise on hemostasis: a systematic review of randomized and non-randomized trials.] International Journal of General Medicine. 2019;12:91.</ref> to examine the safety along with short- and long-term effects of BFR exercise on blood hemostasis in healthy individuals and patients demonstrate that short-term BFR exercise does not exacerbate the activation of the coagulation system nor enhance fibrinolytic activity in young healthy subjects. The findings posit that BFR would be relatively safe for adults considered young and healthy, those who are middle-aged with stable ischemic heart disease, and older healthy adults. But the review also suggests the need to verify the effects of BFR exercise on hemostasis and its safety of BFR exercise on hemostasis as there is limited evidence available.


In this review, they raised concerns about the following<ref name=":11" />
* Adverse effects were not always reported
* The level of prior training of subjects was not indicated which makes a significant difference in physiological response
* Pressures applied in studies were extremely variable with different methods of occlusion as well as criteria of occlusion
* Most studies were conducted on a short-term basis and long term responses were not measured
* The studies focused on healthy subjects and not subjects with risk for thromboembolic disorders, impaired fibrinolysis, diabetes and obesity
Their final conclusion on the safety of BFR was as such:<ref name=":11" />


'''“Thus practitioners must consider the evidence available and ask'''
#'''If the client is sufficiently similar to the subjects in the studies you have examined'''
#'''Does the treatment have a clinically relevant benefit that outweighs the potential risk?'''
#'''Is another treatment available that would provide greater results?" <ref name=":11" />'''
{{#ev:youtube|watch?v=OZjn6vAXJSE}}<ref>Resistance training and coagulation system - Video Abstract ID 194883 Dove Medical Press Available at https://www.youtube.com/watch?v=OZjn6vAXJSE </ref>
{{#ev:youtube|watch?v=OZjn6vAXJSE}}<ref>Resistance training and coagulation system - Video Abstract ID 194883 Dove Medical Press Available at https://www.youtube.com/watch?v=OZjn6vAXJSE </ref>


==== '''Muscle Damage''' ====
In general, it is well established that unaccustomed exercise results in muscle damage and [[Delayed onset muscle soreness (DOMS)|delayed onset muscle soreness]] (DOMS), especially if the exercise involves a large number of eccentric actions. DOMS is normal after unaccustomed exercise, including after LL-BFR training, and should subside within 24–72 hours[[Blood Flow Restriction Training|[2]]].


2. Muscle Damage
High-load Resistance exercise in any form can result in muscle damage. Excessive breakdown of striated muscle is known as exertional [[rhabdomyolysis]] and can result in organ damage.<ref name=":12" /> The incidence of rhabdomyolysis from BFR-RE is very low at approximately 0,07%-0,2%. This seems to be similar to the occurrence of rhabdomyolysis during normal high load resistance training. There is concern that even with low-load BFR, the increased metabolic stress may trigger rhabdomyolysis but the incidence levels are so low the current evidence does not suggest there is increased risk of rhabdomyolysis during BFR-RE compared to other forms of resistance exercise. <ref name=":12" /> However, a recent systematic review analyzing the evidence about muscle damage after resistance training sessions with blood flow restriction suggests that the use of BFR at high loads of training until muscle failure leads to marked levels of muscle damage, and should be avoided. The findings emphasizes that the magnitude of the muscle damage seems to be attenuated after a first session of resistance training with BFR, demonstrating a protective load effect through this type of exercise. Therefore, professionals can use a principle of progressive overload in structuring resistance training with BFR programs in clinical contexts.<ref>de Queiros VS, Dos Santos ÍK, Almeida-Neto PF, Dantas M, de França IM, Vieira WH, Neto GR, Dantas PM, Cabral BG. [https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0253521 Effect of resistance training with blood flow restriction on muscle damage markers in adults]: A systematic review. Plos one. 2021 Jun 18;16(6):e0253521.</ref>
 
Data from the aforementioned surveys found the incidence of excessive muscle damage (i.e., rhabdomyolysis) to be <0.01%. The amount of muscle damage associated with BFR training is conflicting; however, a comparison between maximal eccentric actions and LL-BFR training to exhaustion in untrained individuals revealed comparable amounts of exercise-induced muscle damage. However, performing LL-BFR training to exhaustion in clinical populations is not recommended, therefore, it appears the risk of LL-BFR training resulting in excessive muscle damage is minimal. In general, it is well established that unaccustomed exercise results in muscle damage and delayed onset muscle soreness (DOMS), especially if the exercise involves a large amount of eccentric actions. DOMS is normal after unaccustomed exercise, including after LL-BFR training, and should subside within 24–72 hours<ref name=":3" />.
 
3. Central Cardiac Responses
 
Research studies suggest <ref>Bunevicius K, Sujeta A, Poderiene K, Zachariene B, Silinskas V, Minkevicius R, Poderys J. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5276745/ Cardiovascular response to bouts of exercise with blood flow restriction]. Journal of physical therapy science. 2016;28(12):3288-92.</ref> that the cardiovascular system during exercise does not experience higher overload, which could be a risk factor for cardiac patients and physically inactive persons. This type of exercising could be considered safe.
 
4. Peripheral Vascular Changes
 
The effects of exercise on peripheral vascular changes are mixed. With ageing, the arterial compliance decreases and the resistance exercise may increase arterial stiffness in the elderly. Ozaki et al (Ozaki 2011) found significantly improved arterial compliance after 10 weeks of BFR walking in the elderly population. Clark et al (Clark 2011) found no change in arterial stiffness after 4 weeks of BFR training<ref name=":2" />.
 
5. Tourniquets


==== '''Use of Tourniquets''' ====
By using the 3rd generation system the risk of tourniquet complication is very low, ranging from 0.04% to 0.8%. However, there is an inherent risk to tourniquet use. Some of the common complications<ref name=":2" /> are:
By using the 3rd generation system the risk of tourniquet complication is very low, ranging from 0.04% to 0.8%. However, there is an inherent risk to tourniquet use. Some of the common complications<ref name=":2" /> are:
* Nerve injury: Mechanical compression and neural ischemia play an important role.<ref>JP Sharma, R Salhotra - Indian journal of orthopaedics, 2012 [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3421924/ Tourniquets in orthopaedic surgery]. Indian J Orthop.Jul-Aug 2012, v.46(4).
* [[Nerve Injury Rehabilitation Physiotherapy|Nerve injury]]: Mechanical compression and neural ischemia play an important role.<ref>JP Sharma, R Salhotra - Indian journal of orthopaedics, 2012 [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3421924/ Tourniquets in orthopaedic surgery]. Indian J Orthop.Jul-Aug 2012, v.46(4).
</ref> Nerve injury can range from mild transient loss of function to irreversible damage and paralysis.  
</ref> Nerve injury can range from mild transient loss of function to irreversible damage and paralysis.
* Skin injury
* [[Skin]] injury
* Tourniquet pain
* Tourniquet pain
* Chemical Burns
* Chemical Burns
* Respiratory, Cardiovascular, Cerebral circulatory and haematological effects caused by prolonged ischaemia
* Respiratory, Cardiovascular, Cerebral circulatory and hematological effects caused by prolonged ischemia
* Temperature changes
* Temperature changes


== Summary ==
== Summary ==
BFR training can be viewed as an emerging clinical modality to achieve physiological adaptations for individuals who cannot safely tolerate high muscular tension exercise or those who cannot produce volitional muscle activity. However, continued research is needed to establish parameters for safe application prior to widespread clinical adoption<ref name=":3" />. 
BFR training can be viewed as an emerging clinical modality to achieve physiological adaptations for individuals who cannot safely tolerate high muscular tension exercise or those who cannot produce volitional muscle activity. However, continued research is needed to establish parameters for safe application prior to widespread clinical adoption<ref name=":3" />. "Health care professionals must also make sure they have the proper training and are using the correct BFR equipment and pressure prescription techniques to ensure their patients' safety."<ref name=":7" /> 
 
 




{{#ev:youtube|watch?v=FZWhPx5u9K0}}<ref>Blood Flow Restriction Training American Physical Therapy Association Available at https://www.youtube.com/watch?v=FZWhPx5u9K0</ref>
== Additional Resources ==
<div class="row">
<div class="col-md-4"> {{#ev:youtube|watch?v=FZWhPx5u9K0|250}} <div class="text-right"><ref>Blood Flow Restriction Training American Physical Therapy Association Available at https://www.youtube.com/watch?v=FZWhPx5u9K0</ref></div></div>
  <div class="col-md-4"> {{#ev:youtube|WyQN8ct-TsU|250}} <div class="text-right"><ref>Sports Kongres. Symposium: Blood flow restricted exercise in rehabilitation. Available from: https://youtu.be/WyQN8ct-TsU</ref></div></div>
  <div class="col-md-4">{{#ev:youtube|0umm5WJBNZc|250}} <div class="text-right"><ref>TheIHMC. Jim Stray-Gundersen - Blood Flow Restriction Training: Anti-aging medicine for the busy baby boomer. Available from: https://youtu.be/0umm5WJBNZc</ref></div></div>


== References ==
== References ==
<references />
<references />
[[Category:Course Pages]]
[[Category:Plus Content]]
[[Category:Rehabilitation]]
[[Category:Sports Medicine]]
[[Category:Musculoskeletal/Orthopaedics]]
[[Category:Health Promotion]]
[[Category:Procedures]]

Revision as of 10:30, 8 November 2022

Original Editor - Vidya Acharya

Top Contributors - Vidya Acharya, Mandy Roscher, Kim Jackson, Tarina van der Stockt, Chelsea Mclene, Lucinda hampton, Jess Bell and Olajumoke Ogunleye  


Introduction[edit | edit source]

Muscle weakness commonly occurs in a variety of conditions and pathologies. High load resistance training has been shown to be the most successful means in improving muscular strength and obtaining muscle hypertrophy. However, in certain populations that require muscle strengthening, eg individuals with chronic pain or post-operative patients, high load and high intensity exercises may not be clinically appropriate. Conditions that result in loss of muscle mass such as cancer, Human Immunodeficiency Virus (HIV), diabetes and COPD could potentially benefit from muscle strengthening and muscle hypertrophy but cannot tolerate high intensity/ loaded exercises.[1][2][3][4][5][6]

Blood Flow Restriction (BFR) training is a technique that combines low intensity exercise with blood flow occlusion that produces similar results to high intensity training. It has been used in the gym setting for some time but it is gaining popularity in clinical settings.[7][8]

Blood Flow Restriction (BFR) Training[edit | edit source]

BFR training was initially developed in the 1960s in Japan and known as KAATSU training.[9] It involves the application of a pneumatic cuff (tourniquet) proximally to the muscle that is being trained. It can be applied to either the upper or lower limb. The cuff is then inflated to a specific pressure with the aim of obtaining partial arterial and complete venous occlusion. The patient is then asked to perform resistance exercises at a low intensity of 20-30% of 1 repetition max (1RM), with high repetitions per set (15-30) and short rest intervals between sets (30 seconds) [10]

BFR and Strength Training[edit | edit source]

Understanding the Physiology of Muscle Hypertrophy[edit | edit source]

Muscle hypertrophy is the increase in diameter of the muscle as well as an increase of the protein content within the fibres. An increase in cross-sectional area of the muscle directly correlates with an increase in strength. [11]

Muscle tension and metabolic stress are the two primary factors responsible for muscle hypertrophy. 

Mechanical Tension and Metabolic Stress[edit | edit source]

When a muscle is placed under mechanical stress, the concentration of anabolic hormone levels increase. The activation of myogenic stem cells and the elevated anabolic hormones result in protein metabolism and as such muscle hypertrophy can occur. [12][13]

Release of hormones, hypoxia and cell swelling occur when a muscle is under metabolic stress.[14] These factors are all part of the anabolism of muscle tissue. 

Activation of myogenic stem cells[edit | edit source]
Myogenesis

Myogenic stem cells (satellite cells), are found between the basal lamina and plasma membrane of myofibres. They are normally inactive and become activated in response to muscle injury or increased muscle tension. These cells are responsible for both repair of damaged muscle fibres and also the growth of the fibres themselves[11].

Release of hormones[edit | edit source]
HGH function

Any exercise, resistance or aerobic, brings about a significant increase in human growth hormone (HGH). Insulin-like growth factor and growth hormone are responsible for increased collagen synthesis after exercise and aids muscle recovery. Growth hormone itself does not directly cause muscle hypertrophy but it aids muscle recovery and thereby potentially facilitates the muscle strengthening process.[15] The accumulation of lactate and hydrogen ions (eg in hypoxic training) further increases the release of growth hormone. [13]

High intensity training has been shown to down regulate myostatin and thereby provide an environment for muscle hypertrophy to occur.[12] Myostatin controls and inhibits cell growth in muscle tissue. It needs to be essentially shut down for muscle hypertrophy to occur. 

Hypoxia[edit | edit source]

Resistance training results in the compression of blood vessels within the muscles being trained. This causes an hypoxic environment due to a reduction in oxygen delivery to the muscle. As a result of the hypoxia hypoxia-inducible factor (HIF-1α) is activated. This leads to an increase in anaerobic lactic metabolism and the production of lactate.[14] 

Cell Swelling[edit | edit source]

When there is blood pooling and an accumulation of metabolites cell swelling occurs. This swelling within the cells causes an anabolic reaction and results in muscle hypertrophy.[16] The cell swelling may actually cause mechanical tension which will then activate the myogenic stem cells as discussed above.

Effects of Blood Flow Restriction on Muscle Strength[edit | edit source]

The aim of BFR training is to mimic the effects of high intensity exercise by recreating a hypoxic environment using a cuff. The cuff is placed proximally to the muscle being exercise and low intensity exercises can then be performed. Because the outflow of blood is limited using the cuff capillary blood that has a low oxygen content collects and there is an increase in protons and lactic acid, the same physiological adaptations to the muscle (eg release of hormones, hypoxia and cell swelling) will take place during the BFR training and low intensity exercise as would occur with high intensity exercise.[16]

  • Low intensity BFR training results in greater muscle circumference when compared with normal low intensity exercise. (1)
  • Low intensity BFR (LI-BFR) results in an increase in the water content of the muscle cells (cell swelling).[16] It also speeds up the recruitment of fast-twitch muscle fibres.[17] It is also hypothesized that once the cuff is removed a hyperemia (excess of blood in the blood vessels) will form and this will cause further cell swelling.[10]
  • Short duration, low intensity BFR training of around 4-6 weeks has been shown to cause a 10-20% increase in muscle strength. These increases were similar to gains obtained as a result of high-intensity exercise without BFR[17]

A study comparing (1) high intensity, (2) low intensity, (3) high and low intensity with BFR and (4) low intensity with BFR. While all 4 exercise regimes produced increases in torque, muscle activations and muscle endurance over a 6 week period - the high intensity (group 1) and BFR (groups 3 and 4) produced the  greatest effect size and were comparable to each other. [18]

Equipment[edit | edit source]

BFR Cuff[edit | edit source]

BFR requires a tourniquet to be placed on a limb. The cuff needs to be tightened to a specific pressure that occludes venous flow while still allowing arterial flow whilst exercises are being performed.  

Simple pieces of equipment such as surgical tubing or elastic straps have been used in gym settings to achieve this result.[19] These are not advisable as you are unable to monitor the amount of blood flow occlusion. A thin diameter may also cause too much local pressure and result in tissue damage. 

BFR Cuff Width[edit | edit source]

A wide cuff is preferred in the correct application of BFR. 10-12cm cuffs are generally used. A wide cuff of 15cm may be best to allow for even restriction. Modern cuffs are shaped to fit the natural contour of the arm or thigh with a proximal to distal narrowing. There are also specific upper and lower limb cuffs that allow for better fitment.[20]

BFR Cuff Material[edit | edit source]

BFR cuffs can be made from either elastic or nylon. The narrower cuffs are normally elastic and the wider nylon. With elastic cuffs there is an initial pressure even before the cuff is inflated and this results in a different ability to restrict blood flow as compared with nylon cuffs.[21]

Elastic cuffs have been shown to provide a significantly greater arterial occlusion pressure as opposed to nylon cuffs. [22]

BFR Cuff Pressure[edit | edit source]

Different blood flow restriction cuff pressure prescription methods:[20]

  1. a standard pressure (used for all patients) for e.g. 180 mmHg;
  2. a pressure relative to the patient's systolic blood pressure, for e.g. 1.2- or 1.5-fold greater than systolic blood pressure;
  3. a pressure relative to the patient's thigh circumference.

It is the safest to use a pressure specific to each individual patient, because different pressures occlude the amount of blood flow for all individuals under the same conditions.[20]

A Doppler ultrasound or plethysmography can be used to determine the blood flow to the limb. The cuff is inflated to a specific pressure where the arterial blood flow is completely occluded. This known as limb occlusion pressure (LOP) or arterial occlusion pressure (AOP). The cuff pressure is then calculated as a percentage of the LOP, normally between 40%-80%. 

Using this method is preferable as it ensures patients are  exercising at the correct pressure for them and the type of cuff being used. It is safer and makes sure that they are exercising at optimal pressures, not too high to cause tissue damage and also not too low to be ineffective.[20]

The pressure of the cuff depends upon the width of the cuff as well as the size of the limb on which the cuff is applied. 

The key to BFR is that the pressure needs to be high enough to occlude venous return and allow blood pooling but needs to be low enough to maintain the arterial inflow [23]Perceived wrap tightness, on a scale of 0-10 has also been used to conduct BFR training. Wilson et al (2013) found that a perceived wrap tightness of 7 out of 10 resulted in total venous occlusion but still allowed arterial inflow.  [24][25]

Clinical Application[edit | edit source]

BFR has been used in athletes and recreational training to obtain muscle hypertrophy. It can also be used in clinical populations that cannot perform high intensity exercises because of the stage of their condition or pathology involved.[26]


Examples of BFR training in the clinic:

[27]
[28]
[29]

Procedure[edit | edit source]

Upper Limb:  The tourniquet is placed on the upper arm. The cuff is inflated to restrict 50% of the arterial blood flow and 100% of the venous flow.  

Lower limb: The tourniquet is placed on the upper thigh. The cuff is inflated to restrict 80% of the arterial blood flow and 100% of the venous flow. With the cuff inflated to the correct pressure normal exercises are performed at about 20-30% of 1RM. 

Exercise Prescription[edit | edit source]

Exercise prescription for BFR varies, this is dependent on whether it is being applied during resistance training (BFR-RE), aerobic training (BFR-AE) or passively without exercise (P-BFR)[30]

Model of exercise prescription with BFR-RE[30]

BFR-RE (resistance training)[edit | edit source]

Model of exercise prescription with BFR-AE[30]

For optimal results, resistance training should ideally be done 2-4 times per week. In theory, strength training with BFR can be done daily, however, this may not be the best long term strategy and training 1-2 times per day should only be done for shorter time periods of 1-3 weeks.  BFR-RE is typically a single joint exercise modality for strength training.[30]

Muscle hypertrophy can be observed during BFR-RE within a 3 week period but most studies advocate for longer training durations of more than 3 weeks.

A load of 20-40% 1RM has been shown to produce consistent muscle adaptations for BFR-RE. 

  • The most commonly used training volume in literature is 75 repetitions across 4 sets (30, 15, 15, 15).
  • Rest periods between sets are normally about 30-60 seconds.
  • It is important to keep the cuff inflated during the rest periods to capture the metabolites. Intermittent pressure can be applied however this is not as effective as continuous.[30]
Model of Exercise Prescription with P-BFR[30]

The amount of pressure needed to occlude blood flow in the limb depends on the limb size, underlying soft tissue, cuff width and device used. The arterial occlusion pressure applied is dependent on whether it is an upper or lower limb and should be between 40%-80%.[30]

BFR-AE (aerobic training)[edit | edit source]

BFR can be applied during aerobic exercise and in research has normally been applied during walking or cycling. It is somewhat more difficult to maintain cuff pressures and literature lacks standardization of cuff pressures during BFR-AE.[30]Also, there is limited evidence that BFR training improves aerobic capacity and performance in trained athletes.[31]

P-BFR (passively without exercise)[edit | edit source]

Passively applied BFR (i.e. BFR is applied and no exercise is performed) has not been widely researched. However, it has shown positive results in reducing muscle atrophy post ACL surgery. The studies conducted did not use standardised pressures and some pressures used were high enough to possibly completely occlude blood flow, which poses safety risks. P-BFR could potentially be beneficial in postoperative patients however more research is needed in this field.[30]

Side Effects[edit | edit source]

Reported side effects while performing BFR exercises are fainting and dizziness, numbness, pain and discomfort, delayed onset muscle soreness[32].

Contraindications[edit | edit source]

All patients should be assessed for the risks and contraindications to tourniquet use before BFR application.

  • Patients possibly at risk of adverse reactions are those with poor circulatory system, obesity, diabetes, arterial calcification, sickle cell trait, severe hypertension, or renal compromise[33].
  • Potential contraindications to consider are venous thromboembolism, peripheral vascular compromise, sickle cell anemia, extremity infection, lymphadenectomy, cancer or tumor, extremity with dialysis access, acidosis, open fracture, increased intracranial pressure vascular grafts, or medications known to increase clotting risk[13].

Safety Implications[edit | edit source]

Safety implications around BFR are conflicting. Safety concerns are mainly around the formation of venous thromboembolism (deep vein thrombosis and pulmonary embolism) and muscle damage.[20] Different safety concerns and implications are discussed below:

Blood hemostasis and BFR[edit | edit source]

Blood has the ability to clot through various systems of coagulation. Blood coagulation is kept in check in part by the fibrinolytic system. Fibrinolysis can help prevent the progression of a blood clot into a venous thromboembolism.

A systematic review conducted by da Cunha Nascimento et al in 2019 examined the long and short term effects on blood hemostasis (the balance between fibrinolysis and coagulation). It concluded that more research needs to be conducted in the field before definitive guidelines can be given.[34]

In this review, they raised concerns about the following[34]

  • Adverse effects were not always reported
  • The level of prior training of subjects was not indicated which makes a significant difference in physiological response
  • Pressures applied in studies were extremely variable with different methods of occlusion as well as criteria of occlusion
  • Most studies were conducted on a short-term basis and long term responses were not measured
  • The studies focused on healthy subjects and not subjects with risk for thromboembolic disorders, impaired fibrinolysis, diabetes and obesity

Their final conclusion on the safety of BFR was as such:[34]

“Thus practitioners must consider the evidence available and ask

  1. If the client is sufficiently similar to the subjects in the studies you have examined
  2. Does the treatment have a clinically relevant benefit that outweighs the potential risk?
  3. Is another treatment available that would provide greater results?" [34]

[35]

Muscle Damage[edit | edit source]

In general, it is well established that unaccustomed exercise results in muscle damage and delayed onset muscle soreness (DOMS), especially if the exercise involves a large number of eccentric actions. DOMS is normal after unaccustomed exercise, including after LL-BFR training, and should subside within 24–72 hours[2].

High-load Resistance exercise in any form can result in muscle damage. Excessive breakdown of striated muscle is known as exertional rhabdomyolysis and can result in organ damage.[30] The incidence of rhabdomyolysis from BFR-RE is very low at approximately 0,07%-0,2%. This seems to be similar to the occurrence of rhabdomyolysis during normal high load resistance training. There is concern that even with low-load BFR, the increased metabolic stress may trigger rhabdomyolysis but the incidence levels are so low the current evidence does not suggest there is increased risk of rhabdomyolysis during BFR-RE compared to other forms of resistance exercise. [30] However, a recent systematic review analyzing the evidence about muscle damage after resistance training sessions with blood flow restriction suggests that the use of BFR at high loads of training until muscle failure leads to marked levels of muscle damage, and should be avoided. The findings emphasizes that the magnitude of the muscle damage seems to be attenuated after a first session of resistance training with BFR, demonstrating a protective load effect through this type of exercise. Therefore, professionals can use a principle of progressive overload in structuring resistance training with BFR programs in clinical contexts.[36]

Use of Tourniquets[edit | edit source]

By using the 3rd generation system the risk of tourniquet complication is very low, ranging from 0.04% to 0.8%. However, there is an inherent risk to tourniquet use. Some of the common complications[13] are:

  • Nerve injury: Mechanical compression and neural ischemia play an important role.[37] Nerve injury can range from mild transient loss of function to irreversible damage and paralysis.
  • Skin injury
  • Tourniquet pain
  • Chemical Burns
  • Respiratory, Cardiovascular, Cerebral circulatory and hematological effects caused by prolonged ischemia
  • Temperature changes

Summary[edit | edit source]

BFR training can be viewed as an emerging clinical modality to achieve physiological adaptations for individuals who cannot safely tolerate high muscular tension exercise or those who cannot produce volitional muscle activity. However, continued research is needed to establish parameters for safe application prior to widespread clinical adoption[7]. "Health care professionals must also make sure they have the proper training and are using the correct BFR equipment and pressure prescription techniques to ensure their patients' safety."[20] 



Additional Resources[edit | edit source]

[38]
[39]
[40]

References[edit | edit source]

  1. ↑ Hamilton, David & MacKenzie, Matthew & Baar, Keith. (2009). Molecular mechanisms of skeletal muscle hypertrophy Using molecular biology to understand muscle growth. Accessed from https://www.researchgate.net/publication/235702201_Using_molecular_biology_to_understand_muscle_growth/stats
  2. ↑ Miller BC, Tirko AW, Shipe JM, Sumeriski OR, Moran K. The systemic effects of blood flow restriction training: a systematic review. Int J Sports Phys Ther. 2021 Aug 2;16(4):978-90.
  3. ↑ Wooten SV, Fleming RYD, Wolf JS Jr, Stray-Gundersen S, Bartholomew JB, Mendoza D, et al. Prehabilitation program composed of blood flow restriction training and sports nutrition improves physical functions in abdominal cancer patients awaiting surgery. Eur J Surg Oncol. 2021 Nov;47(11):2952-8.
  4. ↑ Alves TC, Pugliesi Abdalla P, Bohn L, Da Silva LSL, Dos Santos AP, et al. Acute and chronic cardiometabolic responses induced by resistance training with blood flow restriction in HIV patients. Sci Rep. 2022 Oct 10;12(1):16989.
  5. ↑ Jones MT, Aguiar EJ, Winchester LJ. Proposed mechanisms of blood flow restriction exercise for the improvement of type 1 diabetes pathologies. Diabetology. 2021; 2(4):176-89.
  6. ↑ Pitsillides A, Stasinopoulos D, Mamais I. Blood flow restriction training in patients with knee osteoarthritis: Systematic review of randomized controlled trials. J Bodyw Mov Ther. 2021 Jul;27:477-86.
  7. ↑ 7.0 7.1 VanWye WR, Weatherholt AM, Mikesky AE. Blood flow restriction training: Implementation into clinical practice. International journal of exercise science. 2017;10(5):649.
  8. ↑ Loenneke JP, Fahs CA, Rossow LM, Sherk VD, Thiebaud RS, Abe T, Bemben DA, Bemben MG. Effects of cuff width on arterial occlusion: implications for blood flow restricted exercise. European journal of applied physiology. 2012 Aug 1;112(8):2903-12.
  9. ↑ Accessed fromhttps://www.sportsmed.org/AOSSMIMIS/members/downloads/SMU/2017Spring.pdf
  10. ↑ 10.0 10.1 Pope ZK, Willardson JM, Schoenfeld BJ. Exercise and blood flow restriction. The Journal of Strength & Conditioning Research. 2013 Oct 1;27(10):2914-26.
  11. ↑ 11.0 11.1 Bonnieu A, Carnac G, Vernus B. Myostatin in the pathophysiology of skeletal muscle. Current genomics. 2007 Nov 1;8(7):415-22.
  12. ↑ 12.0 12.1 Luke O'Brien. Blood Flow Restriction Therapy Course. Plus. 2019
  13. ↑ 13.0 13.1 13.2 13.3 Johnny Owens. Owens Recovery Science. Blood Flow Restriction Rehabilitation Accessed from https://www.owensrecoveryscience.com/?gclid=EAIaIQobChMIoda_9I6q8AIVxgorCh0YFgd2EAAYASAAEgK3APD_BwE
  14. ↑ 14.0 14.1 de Freitas MC, Gerosa-Neto J, Zanchi NE, Lira FS, Rossi FE. Role of metabolic stress for enhancing muscle adaptations: practical applications. World journal of methodology. 2017 Jun 26;7(2):46.
  15. ↑ Wideman L, Weltman JY, Hartman ML, Veldhuis JD, Weltman A. Growth hormone release during acute and chronic aerobic and resistance exercise. Sports medicine. 2002 Dec 1;32(15):987-1004.
  16. ↑ 16.0 16.1 16.2 Wilson JM, Lowery RP, Joy JM, Loenneke JP, Naimo MA. Practical blood flow restriction training increases acute determinants of hypertrophy without increasing indices of muscle damage. The Journal of Strength & Conditioning Research. 2013 Nov 1;27(11):3068-75.
  17. ↑ 17.0 17.1 Spranger MD, Krishnan AC, Levy PD, O'Leary DS, Smith SA. Blood flow restriction training and the exercise pressor reflex: a call for concern. American Journal of Physiology-Heart and Circulatory Physiology. 2015 Sep 4;309(9):H1440-52.
  18. ↑ Sousa, Jbc et al. “Effects of strength training with blood flow restriction on torque, muscle activation and local muscular endurance in healthy subjects.” Biology of sport vol. 34,1 (2016): 83-90. doi:10.5114/biolsport.2017.63738
  19. ↑ McEwen JA, Owens JG, Jeyasurya J. Why is it Crucial to Use Personalized Occlusion Pressures in Blood Flow Restriction (BFR) Rehabilitation?. Journal of Medical and Biological Engineering. 2019 Apr 2;39(2):173-7.
  20. ↑ 20.0 20.1 20.2 20.3 20.4 20.5 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. journal of orthopaedic & sports physical therapy. 2019 Jan;49(1):17-27.
  21. ↑ Loenneke JP, Fahs CA, Rossow LM, Thiebaud RS, Mattocks KT, Abe T, Bemben MG. Blood flow restriction pressure recommendations: a tale of two cuffs. Frontiers in physiology. 2013 Sep 10;4:249
  22. ↑ Buckner SL, Dankel SJ, Counts BR, Jessee MB, Mouser JG, Mattocks KT, Laurentino GC, Abe T, Loenneke JP. Influence of cuff material on blood flow restriction stimulus in the upper body. The Journal of Physiological Sciences. 2017 Jan 1;67(1):207-15.
  23. ↑ Loenneke JP, Kim D, Fahs CA, Thiebaud RS, Abe T, Larson RD, Bemben DA, Bemben MG. Effects of exercise with and without different degrees of blood flow restriction on torque and muscle activation. Muscle & nerve. 2015 May;51(5):713-21.
  24. ↑ Accessed from https://www.strengthandconditioningresearch.com/blood-flow-restriction-training-bfr/#5 on 16/04/19
  25. ↑ Lowery RP, Joy JM, Loenneke JP, de Souza EO, Machado M, Dudeck JE, Wilson JM. Practical blood flow restriction training increases muscle hypertrophy during a periodized resistance training programme. Clinical physiology and functional imaging. 2014 Jul;34(4):317-21.
  26. ↑ PICÓN MM, CHULVI IM, CORTELL JM, Tortosa J, Alkhadar Y, Sanchís J, Laurentino G. Acute cardiovascular responses after a single bout of blood flow restriction training. International Journal of Exercise Science. 2018;11(2):20.
  27. ↑ NovaCare SelectPT TV. The ACL Road to Recovery - Blood Flow Restriction. Available from: https://youtu.be/FbXSdCm8Q6U
  28. ↑ Performance Physical Therapy & Wellness - Blood Flow Restriction Therapy (BFR). Available from: https://youtu.be/2fMUpxqJq48
  29. ↑ Kate Warren. Blood Flow Restriction Training and Physical Therapy | Breaking Athletic Barriers | EVOLVE PT. Available from: https://youtu.be/pDiLSj6ixTo
  30. ↑ 30.00 30.01 30.02 30.03 30.04 30.05 30.06 30.07 30.08 30.09 30.10 Patterson SD, Hughes L, Warmington S, Burr J, Scott BR, Owens J, Abe T, Nielsen JL, Libardi CA, Laurentino G, Neto GR. Corrigendum: Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety. Frontiers in physiology. 2019;10.
  31. ↑ Castilla-López C, Molina-Mula J, Romero-Franco N. Blood flow restriction during training for improving the aerobic capacity and sport performance of trained athletes: A systematic review and meta-analysis. Journal of Exercise Science & Fitness. 2022 Mar 22.
  32. ↑ Brandner, Christopher & May, Anthony & Clarkson, Matthew & Warmington, Stuart. (2018). Reported Side-effects and Safety Considerations for the Use of Blood Flow Restriction During Exercise in Practice and Research. Techniques in Orthopaedics. 33. 1. 10.1097/BTO.0000000000000259.
  33. ↑ DePhillipo NN, Kennedy MI, Aman ZS, Bernhardson AS, O'Brien L, LaPrade RF. Blood Flow Restriction Therapy After Knee Surgery: Indications, Safety Considerations, and Postoperative Protocol. Arthroscopy techniques. 2018 Oct 1;7(10):e1037-43.
  34. ↑ 34.0 34.1 34.2 34.3 da Cunha Nascimento D, Petriz B, da Cunha Oliveira S, Vieira DC, Funghetto SS, Silva AO, Prestes J. Effects of blood flow restriction exercise on hemostasis: a systematic review of randomized and non-randomized trials. International Journal of General Medicine. 2019;12:91.
  35. ↑ Resistance training and coagulation system - Video Abstract ID 194883 Dove Medical Press Available at https://www.youtube.com/watch?v=OZjn6vAXJSE
  36. ↑ de Queiros VS, Dos Santos ÍK, Almeida-Neto PF, Dantas M, de França IM, Vieira WH, Neto GR, Dantas PM, Cabral BG. Effect of resistance training with blood flow restriction on muscle damage markers in adults: A systematic review. Plos one. 2021 Jun 18;16(6):e0253521.
  37. ↑ JP Sharma, R Salhotra - Indian journal of orthopaedics, 2012 Tourniquets in orthopaedic surgery. Indian J Orthop.Jul-Aug 2012, v.46(4).
  38. ↑ Blood Flow Restriction Training American Physical Therapy Association Available at https://www.youtube.com/watch?v=FZWhPx5u9K0
  39. ↑ Sports Kongres. Symposium: Blood flow restricted exercise in rehabilitation. Available from: https://youtu.be/WyQN8ct-TsU
  40. ↑ TheIHMC. Jim Stray-Gundersen - Blood Flow Restriction Training: Anti-aging medicine for the busy baby boomer. Available from: https://youtu.be/0umm5WJBNZc
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