Blood Flow Restriction Training

Blood Flow Restriction training (BFR) is a novel training strategy that involves the use of an inflatable cuff around the upper thigh or arm which partially restrict arterial inflow during exercise. (1-9)

Traditional strength training requires heavy loads > 60-70% of your 1 repetition maximum (1RM) in order to enhance muscle hypertrophy (size) and strength. (10-14)

The restriction of arterial inflow during BFR is thought to create high levels of metabolic stress and mechanical tension, which are primary mechanisms to induce muscle hypertrophy (size) and strength gains.

BFR training creates a relatively anaerobic (muscle building) environment, allowing muscle size and strength gains to occur at significantly lighter loads of 20-30% 1RM. (1-9)

Photo credit: ESPN Outside the Lines, 2016

Secondary mechanisms of BFR: (1-4,6-8)

• Elevated growth hormone production

• Increased anabolic cell signalling

• Hypoxia

• Cell swelling

• Greater Type II fibre recruitment

• Enhanced protein synthesis

• Proliferation of myogenic stem cells

Benefits of BFR: (2-5,7-9,15-20)

• Improve muscle mass and strength

• Reduce stress on joints, bones, soft tissue

• Allow people who normally couldn’t tolerate weights to strength train

• Analgesic effect

Clinical Populations to Target with BFR: (1-5,7-9,16-19,21-30)

• Post-surgical

• Elderly

• Injured

• Knee Osteoarthritis

• Pain inhibited (i.e. Patellofemoral pain)

• Persistent strength deficits

• Tendinopathies (Achilles, Elbow, Patellar)

Safety of BFR: (4,8,16,19,24,31-40)

Individuals respond similarly to BFR training and regular exercise. Therefore, anyone not appropriate for regular exercise should not commence BFR training.

The collective literature appears to indicate that a proper prescription of BFR poses little risk of directly causing a venous thromboembolism event.

When compared to resistance training, BFR produces no or insignificant change in:

• Peripheral flow

• Central cardiovascular responses

• Coagulation

• Oxidative stress

• Muscle damage

• Nerve conduction velocity

The literature does make certain safety recommendations:

• Use personalized arterial occlusive pressures (AOP)

• Stay at or below 5-10min of total time under restriction per exercise
  -Allow 3-5 min of reperfusion between exercises

• Wider cuffs restrict blood flow at lower overall pressures with improved comfort (cuffs range from 3-18cm in the literature)

• Follow the low load BFR protocol and do not exercise clients to failure
  -Prevents the risk of exercise induced muscle damage

*There are inherent risks with BFR and thus all patients should be assessed for the risks and potential contraindications prior to BFR application

Comparing BFR to Strength Training (ST)

Training Load:

• BFR: Low = 20-40% 1RM (1-9)

• ST: High = 60-90% 1RM (10-14)

Recovery:

• BFR: <24 hours (4)

• ST: Up to 72 hours (41,42)

Muscle Growth:

• BFR: 1-3 weeks (2,4)

• ST: 6-12 weeks (43)

Exercise-Induced Muscle Damage:

• BFR: Only produces muscle soreness (for ~24 hours post workout (4,7,8,35,40,44)

• ST: All factors increased post workout (4,40,45)

*Exercise-induced muscle damage (EIMD) creates temporary: (44,45)

• Delayed-onset muscle soreness

• Swelling of exercises limb

• Decreased range of motion

• Reduced force production (strength)

• Increased creatine kinase and myoglobin levels (markers of skeletal muscle damage)

Low Load BFR Protocol (1-5,8)

BFR Pressure Assessment

In order to standardize the application of BFR practitioners should use a percentage of arterial occlusion pression (the amount of pressure required to cease blood flow to a limb) when in the clinical setting. Since individualized cuff pressures are the safest method of application, allowing for proper progression of BFR. (4,36,38)

AOP (Arterial Occlusion Pressure) is influenced by: (4,38,46)

• Blood pressure and body temperature

• BFR cuff shape, width, and length

• Body position

• Limb circumference

• Time of day

AOP can be determined by inflating the cuff being used during exercise up to the point where blood flow ceases (100% AOP) and using a percentage of that pressure (e.g., 50–80% of AOP) during exercise.  

AOP can be established quickly and reliably using Doppler Ultrasound or built in pressure sensors of several commercially available devices. (4,38)

AOP is body position dependent with AOP being highest in standing compared to seated, and lowest in supine. Thus, for accurate prescription during exercise, BFR should be measured in the intended exercise position. (46)

Areas of concern relating to BFR training identified in the literature:

1. Venous Thromboembolism (VTE) (4,24,31-40)

• The collective literature appears to indicate that a proper prescription of BFR poses little risk of directly causing a VTE event

• It’s important to note that the risk of VTE is increased nearly 100-fold in the first 6 weeks following surgery

• Direct blood markers for coagulation are not increased post BFR

• BFR stimulates the fibrinolytic system (controls the advancement of thrombus formation) increasing the secretion and expression of tissue plasminogen activator (which is a marker of fibrinolysis)

• Cuffs or tourniquets do not appear to be an independent risk factor for a VTE

• In the only epidemiological study of BFR in 12 642 participants in Japan
  -Incidence of 0.055% of VTE or 7 who received BFR
  -Lower rate than that reported for the general Asian population (0.2–0.26%)

2. Stasis (31)

• When considering the mechanisms of stasis, and its contribution to the development of VTE, it seems that the very finite use of a wide, partially occluding cuff would likely be of small risk

3. Endothelial Injury (31,33)

• By using proper BFR cuffs and individualized occlusion pressures it safely disperses the compressive cuff pressures over a larger surface area and most likely does not cause focal stresses on the vasculature that could lead to permanent damage

4. Hypercoagulability (4,31)

• BFR does not appear to lead to hypercoagulability, and a proper prescription of BFR may result in fibrinolysis or a prevention of blood clots

5. Potentially excessive hemodynamic/cardiovascular responses (4,35,38)

• When comparing BFR to heavy load strength training, the hemodynamic response appears to increase in a similar manner during both

• Despite the elevations in hemodynamics, the responses appear to be within normal, tolerable limits – even for those with medical comorbidities

• Whilst there is an increase in the central cardiovascular response during exercise, this returns to baseline acutely (5–10 min) post-exercise cessation

6. Muscle damage (32,35,37,38)

• Delayed onset muscle soreness (DOMS) seems to be commonly reported following BFR exercise, and can persist for 24-72 hours post exercise

• It is imperative to note that an episode of DOMS is relatively normal following unaccustomed exercise bouts, or due to higher than expected increases in exercise intensity (ie, external load) or volume (ie, total exercise volume)

• However it is a transient response to the exercise stimulus and not to BFR per se, before muscle soreness levels return to resting levels

• Given that DOMS is often associated with several markers of exercise-induced muscle damage, several different measures for muscle damage have been examined following BFR exercise

• Overall, the affiliated markers of muscle damage appear only slightly increased and/or rapidly return to resting levels

Absolute Contraindications for BFR: (require 3 or more risk factors present) (31)

• Thrombophilia

• Current hospital admission

• >48 hours of immobility in the past month

• In the past 3 months
  -Hospital admission
  -Surgery
  -Malignancy
  -Infection

Potential Contraindications to consider: (24,31-34,38,47)

• Cardiovascular Disease
  E.g. atherosclerotic vessels causing poor blood circulation, cardiopulmonary conditions, coronary artery disease, hemophilia, hypercoagulable states (blood clotting disorders), peripheral vascular disease, unstable hypertension, varicose veins or vascular endothelial dysfunction

• Cancer or Tumor

• Extremity Infection

• Family medical history
  E.g. Atrial fibrillation or heart failure, cancer, clotting disorders, Connective tissue disorders, sickle cell anemia

• Lifestyle factors
  E.g. obesity, pregnancy, smoking or uncontrolled diabetes mellitus

• Lymphadenectomy

• Medications known to increase clotting risk

• Musculoskeletal injury
  E.g. open fracture, open soft tissue injury, postsurgical excess swelling, recent muscle trauma / crush injury, or skin graft

• Post Surgery
  The risk of VTE is increased nearly 100-fold in the first 6 weeks following surgery

• Renal compromise or Chronic Kidney Disease

• Rheumatoid arthritis

• Venous thromboembolism (current or history)

*This is not an exhaustive list, and it is recommended that all patients be screened before BFR

When to begin BFR Post Surgery

Post-surgery, the primary goal is to resolve pain while re-establishing normal joint movement, muscle hypertrophy (size), strength, and function.

A serious issue during early stages of rehabilitation post-surgery is that patients are often restricted by pain, joint limitations, swelling, weakness and weight-bearing status. (31)

Resulting in patients being unable to fully participate in strength training, as it requires heavy loads of > 60-70% of their 1 repetition maximum (1RM) in order to enhance muscle hypertrophy (size) and strength. (10-14)

BFR training creates a relatively anaerobic (muscle building) environment, allowing muscle size and strength gains to occur at significantly lighter loads of 20-30% 1RM.(1-9) This makes BFR an appealing tool to optimize the post-surgical rehabilitation process. Notably since BFR is generally well tolerated and regarded as safe for most healthy active adults. Along with the fact that advancements in the research surrounding BFR, technology, standardized protocols and individualized cuff pressure prescriptions have markedly enhanced safety. (31) 

Yet the concern regarding the potential for BFR to increase the risk of venous thromboembolism (VTE) which may present as deep vein thrombosis (DVT) or pulmonary embolism (PE) remains for some clinicians, especially for their post-surgical patients.

The collective literature appears to indicate that a proper prescription of BFR poses little risk of directly causing a VTE event. (31)

 It’s important to note that the risk of VTE is increased nearly 100-fold in the first 6 weeks following surgery.  Since VTE risk is highest in the first 6 weeks following surgery, some health care providers may choose to wait until after this period of elevated risk to provide BFR. (31) However, this is also a time frame in which the patient may stand to benefit the most from BFR, as in the first 5 days post-surgery there can be significant muscular atrophy, leading to a 20-30% loss of muscular size and strength during the first 12 weeks post-surgery. (48)

All surgeries will cause some degree of vascular damage no matter if they are open or arthroscopic. However arthroscopic surgeries are less invasive, which could explain which the incidence of VTE is lower following arthroscopic procedures. (31)

When examining the literature surround BFR post arthroscopic ACL repair, it appears to be introduced as early as 7-14 days post-surgery with no reported adverse effects or detrimental consequences to knee joint laxity. Further BFR helped to improve muscle hypertrophy and strength with a greater reduction in knee joint pain and effusion, leading to greater overall improvements in physical function. (48-52)

This makes BFR a vital tool during post-surgical rehab, as a major consequence of ACL injury and surgery is skeletal muscle atrophy and muscle weakness, which occurs postoperatively and can remain for several years. (48)

In fact, weakness of the Quadriceps muscle group in the operated limb is quite substantial in the first 12 weeks following surgery, often exceeding a 20% loss of size and a 30% loss of strength. This will persist for months to years’ post-surgery, with arthrogenic inhibition (decrease in the recruitment of high threshold type II motor units) and weakness being observed 6 months post-surgery. Further the loss of muscle size or atrophy when compared to the contralateral limb has been found to be 7% at 12 months and 3% at 18 months post-surgery. (48)

Finally for the chronic post knee surgery cases (ACL repair, partial or total knee replacements, meniscus repairs and others) that don’t respond to traditional rehabilitation, BFR can help to produce significant improvements in Quadriceps and Hamstring strength. Even in patients who have failed to respond to months of standard post-surgical rehabilitation. Helping them to return to normal ambulation, activities of daily living, occupations and/or athletics. (29)

Anabolic Resistance

Anabolic resistance (AKA disuse atrophy) is the reduction in muscle protein synthesis (MPS) that occurs with physical inactivity.(1,53)  Physical inactivity is common following injury or surgery, leading to a loss of both the quantity and quality of muscle (atrophy) and bone.(16)  Creating a reduced exercise capacity, impaired immune system, increased risk of chronic diseases and numerous other health consequences. (3,10,53-59)

Strength training acutely increases MPS, although the anabolic response is blunted with aging. This may be due to the elderly typically lifting a significantly lower volume and intensity of weights than younger individuals. (53)

Often post injury or surgery there needs to be a delay in high intensity training to allow healing of damaged or repaired areas.  With early rehabilitation typically involving low-load exercises which are insufficient to stimulate MPS or reverse the state of anabolic resistance. (1)

BFR creates a substantial increase in MPS in both young and elderly subjects, that lasts >24 hours post session. (1,2,4,5,7,8,16,60)  Helping to reverse the state of anabolic resistance in those who are physically inactive (injury, post-surgical) and/or elderly.

Furthermore, since the elderly often cannot train as comfortably at the relatively high loads (>60-70% 1RM) required to build muscle size and strength. BFR offers a novel and exciting strategy to prevent anabolic resistance, remove the high joint forces associated with traditional heavy load strength training and enhance health across the entire lifespan.(16,53)

Aging and Osteoarthritis

Aging is generally related to a loss of muscle mass and strength, leading to: (53,61)

• Falls

• Feelings of weakness

• Functional decline

• Loss of independence

However, the decline may be more due to a sedentary lifestyle or periods of muscle disuse (i.e. illness or injury) than actual muscular aging. (53,61)

Exercise can mitigate the loss of muscle mass and strength, along with reducing the risk of: (10,54-59)

• Anxiety and Depression

• Cognitive decline

• Coronary heart disease

• Diabetes

• Falling

• Hypertension

• Obesity

• Stroke

• Some forms of Cancer

Challenging the belief that aging represents an inevitable decline from able to frail. (61)

Photo credit Wroblewski et al. 2011

Quadricep weakness is one of the earliest clinical findings in knee osteoarthritis (OA). In fact, the quadriceps will be 15-38% weaker than age matched healthy knees. With the weakness gradually occurring, leading to: (62-64)

• Joint pain

• Instability

• Stiffness

• Reduced physical activity

• Functional disability 

Increasing quadricep strength had been shown to improve function, reduce pain and potentially prevent the onset of OA symptoms in the knee. Unfortunately, joint pain due to OA symptoms often prevents full activation of the muscles (arthrogenic inhibition) making it difficult to use enough load to build strength. (16,62-64)

Thus, BFR is a useful tool to help increase strength with low loads, while simultaneously reducing pain, swelling, and anabolic resistance. (3-5,8,16,62)

BFR Clinical Pathway

1. Attempt traditional heavy load strength training

2. Educate on BFR safety concerns and benefits

3. Clear potential contraindications

4. Measure Arterial Occlusion Pressure (AOP) with machine or handheld doppler

5. Implement low load BFR protocol 2-3x/week
   -Start at 50% AOP to mitigate DOMS
   -Ensure concurrent home program

6. Advance patient to traditional strength training when able

7. Use experience of metabolic stress to anchor patient’s future expectations of exercise intensity

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