Blood Flow Restriction
INTRODUCTION:
It has been established that in order to gain muscular strength and hypertrophic adaptations individuals must engage in moderate-to-high resistance exercises at intensities >65% of their 1-repitition maximum (1RM) (5-7, 10-14, 18, 21-23). Blood Flow Restriction Training (BFR) involves restricting blood flow proximal to an exercising muscle in an attempt to reduce venous return from the limb, resulting in an accumulation of metabolites that increase muscle force and promotes muscle growth (25). Combined with low-intensity <50% resistance exercises BFR has been demonstrated to effectively take advantage of normal physiological adaptations to exercise by mimicking the metabolic environment necessary to stimulate muscle growth via inducing the same mechanisms of mod-to-high-intensity resistance training through the artificial method of restricting blood flow (22, 25), resulting in muscular strength and hypertrophic adaptations.
Originally, BFR was established as KAATSU training which involves low-intensity exercise and a KAATSU cuff, which is a specified airbag-contained belt that connects to an electric pressure control system to allow monitoring of restriction pressure (32). However, due to issues such as practicality (i.e. cost) blood pressure cuffs, and now more popularised knee wraps, are largely utilised methods for occlusion training (15). One of the most important factors of BFR was indeed the cuff width. Wider cuffs are renown for a higher perceived pain ratings, can inhibit functionality and they also transmit pressure differently to narrower cuffs (22, 31). In regards to restrictive pressure, the perceived pressure rating of 7 out of 10 is generally considered as the practical method of effective occlusion (31), but pressure should vary relative to each individual. Exercise protocols of BFR generally coincide with the following guidelines; Both single and multi-joint exercises can be utilised, 3-5 sets ranging in-between 50-80 reps per exercise, with 30 seconds to a 1 minutes rest, at a low-load intensity <50% 1RM or MVC, 2-3 sessions per-week (22). Essentially, KAATSU training, Vascular Occlusion Training (VOT) and BFR are now protocols of the same nature. The purpose of this review was to discuss the concepts of BFR, to analyse, and to provide coaches, athletes and strength and conditioning professionals with information on the mechanisms of BFR, a greater knowledge of the benefits of BFR as well as the potential issues associated with blood flow restriction training systems.
DISCUSSION:
There are a vast amount of populations that require muscular strength and hypertrophic adaptations for overall health and wellness. Various exercise modalities required to induce strength and hypertrophic muscular adaptations can be deemed too difficult to induce for specific populations, i.e. the elderly. Effectively, this results in many insufficient and poor training programs being undertaken, negatively impacting health and wellness. The use of BFR as an alternative method to combat issues related to exercising impairment for certain populations is becoming more widely explored, and the mechanisms and adaptive responses associated with its protocols are being further researched and developed. The following information will provide and discuss the potential issues associated with blood flow restriction training systems.
Morphological and Neurological Adaptations
BFR has a copious number of mechanisms involved in its application. The external pressure applied induces an ischemic/hypoxic environment and an accumulation of metabolites that enhances the training effect in exercising muscles leading to increased muscle mass and strength (7, 21, 22). This hypoxic environment and metabolic accumulation results in mechanical tension and metabolic stress.
Metabolic stress was magnified under ischemic/hypoxic conditions, such as during BFR, and has demonstrated to significantly increase muscle cross-sectional area (CSA) similarly to non-BFR training (21), induce muscle growth via increased cell swelling, intramuscular anabolic/anti-catabolic signalling, muscle fast-twitch fibre recruitment, elevations in systemic hormones, increased production of reactive oxygen species (ROC) (which mediates post-workout anabolic adaptations) and the activation and proliferation of myogenic stem cells, enhancing hypertrophic responses (10, 11, 14, 21, 22, 31). Increases in strength via hypoxic conditions are also seen with excessive secretion of neurohumoral factors such as lactate norepinephrine, vascular endothelial growth factor (VEGF) and growth hormone (GH) response (20, 23).
Growth hormone stimulates secretion of Insulin-Like Growth factor-1 (IGF-1), which increases protein synthesis and activates satellite cells, all of which cause myofibril muscle hypertrophy (18). It’s also known to increase glucose and amino acid uptake and promotes protein synthesis for muscle hypertrophy (28). BFR training induced hypoxia accelerates the endothelial nitric oxide synthase (eNOS) expression, which results in an amelioration of endothelial dysfunction (23). This stress to the vascular endothelial cells created by BFR increases eNOS via up-regulation of VEGF and was an important modulator for vasculogenesis, arteriogenesis and angiogenesis essential for hypertrophy, as well as, BFR being shown to improve peripheral blood circulation (18, 20, 23).
Reactive oxygen species may influence anabolism via heat shock protein (HSPs), which act as chaperones aiding in the assembly and translocation of proteins when the body is subjected to stress to maintain cellular homeostasis (14, 21). Specifically, heat shock protein 72 (HSP 72), nitric oxide synthase-1 (NOS-1) and myostatin contribute to increases in CSA (14). Heat shock protein 72 is responsive to BFR induced by heat, hypoxia, free radicals, acidosis, and ischemic-reperfusion (14, 21). NOS-1 stimulates muscle growth through increased satellite cell activation (14). And myostatin (a negative regulator of muscle growth that inhibits cell proliferation (10, 21)) is decreased in response to BFR by increased activation of the mammalian target of rapamycin (mTOR) pathway (14, 21).
Mechanical tension mechanisms that induce muscle hypertrophy include; mechanotransduction (which involves sarcolemmal-bound mechanosensors to convert mechanical energy into chemical signals. These mediate intracellular anabolic and catabolic pathways leading to a shift in muscle protein balance that favours synthesis over degradation (21)), increased localised hormone production, muscle damage, ROS production and fast-twitch fibre recruitment. These factors increase protein synthesis through activation of signalling pathways or satellite cell activation and proliferation for the induction of muscle growth (21). Satellite cells are muscle specific stem cells located under the basal lamina of muscle fibres and responsible for muscle regeneration (21). BFR training has shown increases in satellite cell proliferation, which increases muscle protein synthesis as well as hypertrophy via cell swelling - the phenomenon of increases in intracellular hydration (21). Increases of metabolites from BFR creates a pressure gradient favouring blood flow into muscle fibres, resulting in a greater hyperaemia after reperfusion and subsequent intracellular swelling, which initiates signalling responses that lead to reinforcements of the cell membranes ultrastructure (7, 21). Cell swellings thought to activate an intrinsic volume sensor that results in concurrent activation of mTOR and Mitogen-activated protein kinase (MAPK) signalling pathways. These pathways inhibit catabolism and atrophy associated with Muscle RING-finger protein-1 (MuRF1) and Muscle atrophy Fbox protein (MAFbx) activity, as well as, shifting protein to anabolism, positively affecting metabolism through the sparring of protein and promotion of lipolysis. Thus, leading to greater muscle adaptation and induced hypertrophy (7, 21, 31).
The hypoxic and accumulative metabolic environment has shown EMG activity to be high in BFR, resulting in an increased higher-threshold fast-twitch fibre recruitment by inhibiting the alpha motor neuron. This is achieved through the stimulation of III and IV afferent neurons to maintain force against conduction failure (7, 10, 14, 21, 31), and activation of metaboreceptors increasing sympathetic nerve activity to the muscle, referred to as metaboreflex (14, 28). Increased metabolites also contribute to driving the exercise pressor reflex, which increases both HR and BP (7). For instance, Moore et al. (17) described neuromuscular adaptations to BFR as a task-specific motor unit activation to improve muscle coordination. This was seen by improvements in 1RM and isometric strength, increased EMG activity and increased motor unit synchronisation leading to overall electromyography (EMG) interference amplitude. These increased EMG signals and a rise in recruitment.
Changes in bone mass are a result of bone formation and resorption, regulated by hormones, growth factors, cytokines and mechanical loading. Loenneke et al. (13) found significant increases in serum bone specific alkaline phosphate (BAP) with BFR Training. BAP levels are considered to reflect osteoblastic activity and can therefore be used as a proxy marker of bone formation (13). These BAP levels suggest there was bone adaptations associated with BFR, which could lead to beneficial use of the BFR training modality for populations such as; athletes returning from broken bone injuries, or older women suffering from osteoporosis.
Possible Causes for Concern
There have been a number of safety issues highlighted by multiple researchers, concerned with the long-term effects that may be harmful with BFR. It’s suggested that severely restricting blood flow, or complete occlusion to the muscle may cause necrosis, blood coagulation and reduced endothelia function (4). Homeostasis is maintained through a balance between coagulation and fibrinolytic activity - exercise is shown to affect both of these processes (12). As exercise activates fibrinolysis, strenuous exercise increases the activity of coagulation, resulting in thrombosis (12). With complete occlusion the formation of thrombosis can induce microvascular occlusion even after reperfusion. This post-reperfusion occlusion can result in muscle damage and necrosis (12). However, coagulation activity does not appear to increase after low-intensity BFR and it appears that BFR actually enhances fibrinolytic potential (12).
Muscle damage increases with elevating intensity and is impacted by the type of muscular contraction, more significantly by eccentric contractions (9, 12). As well as, the amount of strain placed on the muscle, initial muscle length, the force per active area and peak force produced during exercise (9). BFR training has been suggested to result in ischemia-reperfusion muscle damage. This effect however is dependent on the duration and severity of ischemia. During this ischemic period the decrease in muscle oxygen and depletion in energy stores produces an accumulation of metabolites, decreases pH and can also eventuate to cell necrosis (9). Typically, ischemic-reperfusion is used during surgeries to decrease bleeding and is likely minimal in BFR on the basis that occlusion exercise lasts roughly 5-15 minutes, followed by complete reperfusion (9).
It’s been demonstrated that low-intensity exercise combined with partial occlusion has no impact on blood clotting function. It’s assessed by the changes in fibrin D-dimer and fibrin degradation products, and, has no effect on markers of oxidative stress based on the amounts of plasma lipid peroxide, blood glutathione status, plasma protein carbonyls and plasma makers of muscle damage (4).
In regards to restriction and cuff tightness, excessive restriction could lead to over-activation of muscles reflexes and central command, with consequent development of sympathetic hyperactivity, increasing the risk of cardiovascular-related events (25). This is activated by the skeletal muscle exercise pressor reflex (EPR), which functions via two components – the muscle metaboreflex and muscle mechanoreflex (25). Along with central command (feed forward neural signalling from the cerebral cortex) and the arterial baroreflex (neural signal from carotid sinus and aortic arch), the EPR mediates the autonomic cardiovascular system by enhancing sympathetic output while reducing parasympathetic output during exercise. This results in the elevation of mean arterial pressure (MAP) (25). Clearly, the EPR plays a role in regulating the cardiovascular systems; therefore, concerns are raised in regards to individuals performing BFR diagnosed with diseases such as hypertension, heart failure and peripheral artery disease (PAD). The metaboreflex-mediated responses are altered in these diseased individuals, resulting from a generation of sympathetic overactivity (25), as well as, the mechanoreflexs being over-activated in these disease states showing an increase in blood pressure (25). These EPR responses to exercise increases the risk for an occurrence of deleterious cardiovascular or cerebrovascular events (25). Although BFR is performed with light loads, muscle perfusion is mechanically attenuated, therefore engaging EPR responses, and is effectively putting individuals with diagnosed cardiovascular diseases at risk of sympathetic nerve activity (SNA). This can generate abnormal elevations in MAP and coronary vasomotor tone resulting in adverse cardiovascular events such as stroke, aneurysms and myocardial infarctions (12, 25). As pointed out above, excessive restriction could lead to significant ischemia, but also muscle cell swelling secondary to edema, both of which stimulate the EPR. This excessive venous restriction elevates blood pressure, which can damage valves in veins and lead to chronic venous insufficiency (12, 25).
Oxidative stress is a biological phenomenon marked by an imbalance between reactive free radicals and antioxidant defences (12). Severe acute or prolonged chronic oxidative stress can lead to oxidatively modified lipids, proteins and DNA (12), resulting from high-intensity exercise (>70%) and ischemic-reperfusion or hypoxic conditions. However, it has been shown that muscle contractions during BFR were able to overcome venous outflow and thus helped remove oxidative stress markers from circulation, as well as, pressures during contractions being sufficient in enhancing blood flow during muscle contractions, enabling adequate flow delivery to overcome partial vascular restriction (12). A survey of 105 Japanese facilities utilising BFR techniques reported that numbness was sometimes a response to blood flow restrictive exercise (12). Out of 30,000 sessions there were a reported 1.6% of transient side effects to the BFR modality, raising the issue of possible nerve conduction blockage. However this issue potentially was not alarming because BFR lasts 5-15 minutes and the effects of numbness and nerve conduction blockage is usually seen to occur after surgery (12).
One incident of an acute case of Rhabdomyolysis has also been reported (26). Rhabdomyolysis is a serious and life threatening condition that can be associated with resistance training. According to the U.S National Library of Medicine, it’s the breakdown of muscle tissue that leads to the release of muscle fiber contents into the blood. These substances are harmful to the kidney and often cause kidney damage. In the acute case identified, a 30 year old obese Japanese man was admitted to hospital after his first blood flow restricted training session, with complaints of serious muscle pain, high fever and pharyngeal pain (26). Based on a serum creatine phosphokinase level of 56,475 U/l, a urine myoglobin level >3000 ng/ml, an apparent onset of tonsillitis based on a white blood cell count of 17,390 and C-reactive protein level of 10.43 mg/dl, he was diagnosed with Rhabdomyolysis (26). There are a number of factors that can exacerbate rhabdomyolysis, such as; trauma, drugs/medication, genetic muscle disease, extreme body temperature, ischemia, low phosphate levels, seizures and excessive muscular training and severe dehydration. However, this incident was the only reported case in regards to Rhabdomyolysis with BFR (26) and the individual recovered after 10 days without complaints.
An issue that’s raised was the differences in cuff pressures, in that, wider restrictive devices transmit pressure differently to narrower cuffs (12). Applying a 200 mmHg across 50mm KAATSU cuff will produce a different stimulus to 200 mmHg applied with a 135 mm wrap (12). As noted, some of the issues raised can potentially be induced by high-intensity or strenuous exercise, however, manipulating the bodies natural process associated with high-intense exercise via blood flow restriction was inclined to have a call for concern.
Effects on Different Populations
VOT was performed over 4 weeks with National Collegiate Athletic Association Division IA football athletes to investigate its effectiveness on inducing strength and hypertrophy (32). Athletes underwent 1RM testing for the bench press and squat, then were divided into a BFR group, and a non-BFR group, where they then performed 1 set of 30 repetitions at 20% 1RM, followed by 3 sets of 20 repetitions at 20% 1RM in the bench press and squat, with 45 seconds rest between sets, over 3 days a week for a total of 4 weeks, in conjunction to their regular resistance training regime (32). The BFR group achieved significantly greater increases in muscular strength, with an average increase of 7% for the bench press and 8% increase for the squat, compared to that of the 3.2% and 4.9% which was achieved by the non-BFR group, in the bench and squat respectively (32). This is indicative of how BFR can initiate strength and hypertrophy gains via the hypoxic and acidic environment it creates, recruiting additional fast-twitch motor units to maintain force production.
Similarly, other findings reported low-intensity resistance training combined with BFR resulted in muscle size, strength and endurance increases in full trained athletes (27). BFR of the lower extremities caused a 290-fold increase in plasma concentration of growth hormone in the BFR group, a 14.3% increase in strength, as well as approximately 12.3% increase in CSA of the knee extensors (27). Fatigue indices were also measured by the amount of work and average peak torque, comparing the initial 10 contractions and the final 10 contractions during 50 dynamic knee extensions, to determine muscular endurance. Both indices decreased significantly from 63.7% to 58.7%, and 61.3% to 53.7% respectively, indicating a greater efficiency of muscular endurance after BFR (27).
Cook et al. (1) investigated training effects and salivary hormonal responses to an intermittent blood flow restriction training program across an eight week pre-season period for trained rugby athletes. The occlusion cuff consisted of a 10.5cm width, inflated at 180 mmHg, but was only inflated during exercise and deflated during inter-exercise rest periods (1). This form of BFR stimulated exercise significantly, enhancing strength, power and speed due to the resulting hypoxic and acidic intramuscular milieu from the BFR. It increased motor unit recruitment, potentiating the skeletal muscle expression of mRNA responsible for angiogenesis and attenuated the mRNA expression of proteolytic transcripts. Also, it enhanced phosphorylation of downstream targets of the mTOR-signalling pathway and extracellular signal-regulated kinases, increasing muscle protein synthesis (1). The saliva samples displayed elevations in testosterone concentration during exercise, which is related to improved adaptations, indicating the hormones permissive role in actualising specific functional adaptations.
It has been shown that BFR can benefit individuals suffering from Idiopathic body myositis (IMB), a rare idiopathic inflammatory myopathy, known to produce remarkable muscle weakness and greatly compromise function and quality of life (2). Unfortunately the majority of IBM patients are non-responsive to treatments with immunosuppressive or immunomodulatory drugs to counteract the disease (2). IBM patients were recently observed to respond with significant gains in muscle mass, function and quality of life, as a result of BFR in association with moderate resistance training (2). After a 12-week program working with a leg-press, leg extension and half-squat, using the 3 sets of 15 reps, with a 30 seconds rest between sets protocol, IBM patients improved 1RM leg press scores by 15.9%, improved balance and mobility function by 60% and increased thigh CSA by 4.7% (2). Moreover, health survey questionnaires demonstrated improvements ranging from 18% to 600%, indicating a boost in the patient’s quality of life, as well as, mRNA expression of mechanogrowth factor increasing 3.97-fold (2).
These findings are supported by another study that looked at a supervised 12-week low-intensity resistance-training program combined with partial blood flow restriction on patients suffering from Polymyositis (PM) and Dermatomyositis (DM), which are also rare idiopathic inflammatory myopathy conditions, associated with proximal muscle weakness, muscle atrophy, fatigue, myalgia and impairments in distal lower-limb muscle function (16). Again, the leg press and knee extension exercise protocols were utilised, with an occlusion pressure cuff (width 175mm x length 920mm) placed at the inguinal fold of both thighs (16). During first 4-weeks, 4 sets of 15 reps at 30% 1RM was required, followed by 5 sets of 15 reps at 30%1RM from the fifth week onwards (16). The pressure of the cuff was set at 70% of patients predetermined pulse eliminating pressure, with a mean pressure of 94 mmHg (16). Findings demonstrated a 19.6% improvement in the leg press and 25.2% increase in the knee extension. Timed stand-up test scores increased by 15.1% and timed up-and-go test scores improved by -4.5% (decrease in time, meaning they got quicker), CSA significantly increased by 4.57% and there was significant improvements in quality of life measurements (16). These results indicated that BFR is an effective protocol in counteracting muscle weakness, muscle dysfunction, atrophy and quality of life in PM/DM patients. It was also suggested that no exacerbation of the disease was observed which collectively implies BFR to be a safe and effective method for use with PM/DM patients (16).
A comparison study between 2 groups looked at of BFR with elastic bands at low load intensities, matched against mod-to-high intensity elastic band exercises in postmenopausal women (29). The BFR group was assigned to KAATSU-master cuffs (3.3cm x 58cm), where pressure was gradually increased over the course of the study starting at 80 mmHg in the first week, elevating to 120mmHg by the last week (29). Interestingly, performing low-intensity elastic band training with blood flow restriction resulted in similar changes to muscle thickness, total bone-free lean body mass and strength compared with mod-high intensity elastic band exercises (29). Strength increased for all lower body exercises that were tested (leg-press, hip extension, hip flexion, knee extensions and knee flexion), as well as, significant average increases resulting in the chest press (increase of 3.7kgs), the seated row (2.2kgs increase) and shoulder press (1.4kgs increase). However, no differences were found between groups (29). One interesting finding was that the pectoralis major induced the greatest muscle thickness during the BFR, with a 17% increase, even though the pectorals were not occluded. From the findings it was concluded that BFR with bands at low-load intensities could be utilised to improve strength in postmenopausal women, or during rehabilitation when additional stress to joints is contraindicated (29).
Osteoporosis is a metabolic bone disorder characterised by decreased bone mineral density (BMD), with deterioration of bone microarchitecture, most frequently occurring in post menopause (24). With decreases in muscle mass and an associated decreased capacity to produce strength, BMD leads to an increased likely hood of skeletal fragility and fractures due to falls (24). It was noted that resistance training improves the performance of older individuals with osteoporosis, however some of these people cannot endure the high-intensity loads required to impose improvements in muscular strength, joint strength and bone strength, therefore, low-load BFR has been suggested. Silva et al. (24) used a tourniquet pressure cuff at an average tightness of 105 mmHg during a study looking at BFR combined with strength training (ST) on osteoporotic women (24). The main finding was that BFR combined with ST induced a 10.59% increase in maximal dynamic strength in elderly women with osteoporosis over 12 weeks, and that combining BFR with ST two times or more per week will induce gains in maximal dynamic strength, resulting in significant improvements living with osteoporosis (24).
Sarcopenia is a condition associated with the loss of muscle strength and mass with age. It’s a detrimental issue leading to a decline in functional capacity, mobility, endurance, loss of bone-mineral density and an increased rate of falls in the elderly (8, 18, 19, 30). Decreased vascular function and reductions in limb blood flow at rest, during exercise and after reactive hyperaemia, are also seen with ageing, and are associated with metabolic syndrome and impaired clearance of atherogenic lipids that contribute to dyslipidaemia (19). This decreased vascular function can also result in the decline in limb venous compliance, which prevents the elderly from responding to acute deterioration of cardiovascular homeostasis. Further, reduced venous compliance may add to the risk factors of varicose veins and deep vein thrombosis (3). The aim for the ageing individual is to maintain skeletal muscle mass, because skeletal muscle functions as the largest disposal site of ingested glucose, plays an important role in lipid oxidation and contributes to resting metabolic rate (8). Many elderly are contraindicated to the recommendations of high load resistance training >70% 1RM, resulting in a failure to recruit fast twitch fibres and a 20-50% reduction in fast twitch CSA (8). The effects of resistance training may also increase central and peripheral arterial stiffness and sympathetic activity, leading to increase risk of cardiovascular dysfunction (18). BFR is the proposed exercise modality to combat these issue via the variety of mechanisms (fast-twitch fibre recruitment, stimulation of protein synthesis pathway mTOR, increase in GH response) it can stimulate at low-load intensities (8).
It’s been reported that BFR improves strength (3, 18, 19, 23, 30), reduces arterial stiffness, improves cardiovascular function, and is shown to up-regulate mTOR and IGF-1 measurements, which improves muscle protein synthesis (18). It also improves lower limb post-occlusive blood flow (19), improves limb venous compliance and improves maximal venous outflow after 6 weeks of BFR with walking (3). Increases of 18% in MVC have been shown after BFR, as well as increases in isokinetic torque, and BFR has demonstrated to be a tolerable and safe training modality. This is confirmed from reports of elderly participants completing BFR with no complications or complaints and no effects on vascular nerve function or markers of coagulation, fibrinolysis or inflammation (19).
Patients following surgery or serious injury, such as an ACL tear, generally exhibit a loss of function due to the injury, resulting in disuse atrophy. Typically BFR has shown to be beneficial to this population of people, because BFR allows an individual to train at low intensities with the benefits of high-intensities, improving the muscular function lost from previous time spent bedridden (14). Also, in regards to disuse, Astronauts have been deemed to benefit from BFR training. During spaceflight several health concerns arise due to the changes in cardiovascular function from weightlessness (14). When gravitational hydrostatic gradients are abolished, there’s a shift of intravascular fluid from capacitance vessels of the lower body centrally towards the head (14). Almost every astronaut will experience orthostatic hypotension and reduced upright exercise capacity, due to microgravity-induced hypovolemia, decreased baroreflex responsiveness, decrease muscle tone and increased venous compliance (14). BFR was introduced as a countermeasure to combat orthostatic intolerance and muscle atrophy from spaceflight by inducing hemodynamic, hormonal and autonomic alterations.
CONCLUSION AND PRACTICAL APPLICATIONS:
Based on the review of literature, BFR, combined with low-load resistance training <50% 1RM, was deemed a safe, effective and efficient exercise/training modality. Therefore the general population, post-rehabilitative individuals, athletes, coaches, strength and conditioning professionals and the elderly can employ BFR modalities for positive adaptations to muscle strength and hypertrophy. It has been identified that BFR stimulates similar morphological and neurological adaptations that are seen with regular high-intensity resistance training >70% that has previously been determined the benchmark percentage for muscle strength and hypertrophy. Although there are causes for concern associated with VOT, these issues are just as prevalent in regular high-intensity exercise.
Practical Recommendations
For practicality use: Standard knee wraps 5 – 10cm in width or medical tourniquets to be used for both lower and upper limbs. Cuffs should be applied for the duration of the BFR protocol utilised, sets of 30-15-15-15 reps at <50% of 1RM, 30secs rest between sets, with an individual perceived pressure rating of 7/10. For athletes, BFR can be used in conjunction with their regular training schedule as a finisher for muscle hypertrophy, during general preparation. In pre-season BFR can be substituted in on a de-load week or added as variety, again in conjunction to there periodised training program. During, or in-season, BFR can be undertaken to maintain physiological performance gains acquired during the pre-seasonal preparation stages. The amount of sessions of BFR per-week may vary, but 2-3 sessions over a cycle, no longer than 4 - 8 weeks, should be utilised. BFR can also be performed to assist individual with an inability to engage in physical activity, such as the elderly and post operative or return to play/health individuals, via reducing muscle atrophy, following the same protocols. However exercise selection and duration may vary, depending on the individual’s needs, therefore these guidelines are susceptible to change. If available, medical pressurised cuffs can be utilised, and pressures subject to target each individual’s specific arterial flow.
Further research needs to be conducted in regards to the ideal occlusion pressure to stimulate the greatest adaptive responses, and should specifically investigate long term effects (>16 weeks) of BFR as well as different modalities of BFR training, as opposed to the standard modality of 30-15-15-15 with 30 seconds rest between sets. BFR at intensity loads >50% should also be conducted and the effects associated with BFR at these higher loads needs to be addressed.
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