Blood Flow Restriction Training

Original Editor - Vidya Acharya

Top Contributors - Vidya Acharya, Mandy Roscher, Tarina van der Stockt and Kim Jackson  


Introduction

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. The problem that exists is that in certain populations that require muscle strengthening eg Chronic Pain Patients 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, HIV/AIDS, diabetes and COPD could potentially benefit from muscle strengthening and muscle hypertrophy but cannot tolerate high intenstity/ loaded exercises[1]. 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.[2][3]

Blood Flow Restriction (BFR) Training

BFR training was initially developed in the 1960’s in Japan and known as KAATSU training. [4] 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) [5]

BFR and Strength Training

Understanding the Physiology of Muscle Hypertrophy.

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. [6]

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

Mechanical Tension & Metabolic Stress

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. [7][8]

Release of hormones, hypoxia and cell swelling occur when a muscle is under metabolic stress.[9] These factors are all part of the anabolism of muscle tissue. 

Activation of myogenic stem cells

Myogenic stem 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[6].

Release of hormones

Any exercise, resistance or aerobic, brings about a significant increase in growth hormone. 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.[10] The accumulation of lactate and hydrogen ions (eg in hypoxic training) further increases the release of growth hormone. [8]

High intensity training has been shown to down regulate myostatin and thereby provide an environment for muscle hypertrophy to occur.[7] Myostatin controls and inhibits cell growth in muscle tissue. It needs to be essentially shut down for muscle hypertrophy to occur. 

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.[9] 

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.[11] The cell swelling may actually cause mechanical tecnsion which will then activate the myogenic stem cells as discussed above.

Effects of Blood Flow Restriction on Muscle Strength

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.[11]

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).[11] It also speeds up the recruitment of fast-twitch muscle fibres.[12] It is also hypothesised that once the cuff is removed a hyperemia (excess of blood in the blood vessels) will form and this will cause further cell swelling.[5] 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[12]

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 reigmes produced increases in torque, muscle activations and muscle endurance over a 6 week period. The high intensity and BFR groups (1,3 and 4) produced the  greatest effect size and were comparable to each other. [13]

Equipment

BFR Cuff

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.[14] 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

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.[15]

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.[16]

Elastic cuffs have been shown to provide a significantly greater arterial occlusion pressure as opposed to nylon cuffs. [17]

BFR Cuff Pressure

Different blood flow restriction cuff pressure prescription methods:[15]

  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.[15]

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.[15]

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 [18]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.  [19][20]

Clinical Application

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. [21]. Examples of BFR training in the clinic:

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. 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

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)[25]
Model of exercise prescription with BFR-RE[26]

BFR-RE (resistance training)

Model of exercise prescription with BFR-AE[27]
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.[25] 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.[25]
Model of Exercise Prescription with P-BFR[28]
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%.[25]

BFR-AE (aerobic training)

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 standardisation of cuff pressures during BFR-AE.[25]

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.[25]

Side Effects

Reported side effects while performing BFR exercises are fainting and dizziness, numbness, pain and discomfort, delayed onset muscle soreness[29].

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 circulatory systems, obesity, diabetes, arterial calcification, sickle cell trait, severe hypertension, or renal compromise[30]. 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[8].

Safety Implications

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.[15] Different safety concerns and implications are discussed below.

Blood hemostasis

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.[31]

In this review, they raised concerns about the following[31]

  • Adverse effects were not always reported on
  • 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:[31]

“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?" [31]
[32]

Muscle Damage

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.[25] 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. [25]

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[8] are:

  • Nerve injury: Mechanical compression and neural ischemia play an important role.[33] 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 haematological effects caused by prolonged ischaemia
  • Temperature changes

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[2]. "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."[15] 


[34]

Additional Resources

References

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