Blood Flow Restriction (BFR)
Blood flow restriction (BFR) training induces a hypoxic environment within a muscle group, initiating a metabolic cascade that stimulates muscle protein synthesis, altered gene regulation of muscle satellite cells, and increased muscle fiber recruitment, ultimately resulting in improved strength and endurance.
Blood Flow Restriction Training
Introduction: What is BFR?
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, e.g. 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
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
Muscle hypertrophy is the increase in diameter of the muscle as well as an increase of the protein content within the fibers. 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
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]
Key Benefits:
builds muscle strength with low loads
reduces stress on joints and healing tissues
prevents muscle atrophy after injury or surgery
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 exercised 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 (e.g. 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 fibers.[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
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.[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
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
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 significantly greater arterial occlusion pressure as opposed to nylon cuffs. [22]
BFR Cuff Pressure
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 example 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 is 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
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]
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) [30]
Model of exercise prescription with BFR-RE [30]
BFR-RE (resistance training)
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)
BFR can be applied during aerobic exercise and 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)
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 standardized 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]
Who can Benefit?
It’s versatile! Can be used with post operative rehab patients, athletes returning to sport, those with chronic pain, and older adults who need strength training with less joint stress. It’s important to note that BFR is useful when traditional strength training isn’t in the picture yet.
Side Effects & Contraindications
Reported side effects while performing BFR exercises are fainting and dizziness, numbness, pain and discomfort, delayed onset muscle soreness [32].
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].
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.[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 an 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 emphasize 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]