Blood Flow Restriction Training

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

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. 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.

Blood Flow Restriction (BFR) Training

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

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. 

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.

Release of hormones, hypoxia and cell swelling occur when a muscle is under metabolic stress. 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.

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. The accumulation of lactate and hydrogen ions (eg in hypoxic training) further increases the release of growth hormone.

High intensity training has been shown to down regulate myostatin and thereby provide an environment for muscle hypertrophy to occur. 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. 

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. 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.

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). It also speeds up the recruitment of fast-twitch muscle fibres. 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. 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

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.

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. 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.

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.

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

BFR Cuff Pressure

Different blood flow restriction cuff pressure prescription methods:

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.

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.

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 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.  

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. . Examples of BFR training in the clinic:

Procedure

Upper Limb:  The tourniquet is placed on the upper arm. The cuff is inflated to resrict 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

1. Training Frequency

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 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

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.

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

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

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.

7. Exercise Selection

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.

• 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.
• Exercises:

Upper extremity: Upper body ergometer, isometrics, scapular rows, serratus punches, shoulder exercises, proprioceptive neuromuscular facilitation (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.

8. Exercise Progression

Below are guidelines to follow concerning exercise progression and difficulties with volume achievement: Load: 20-30% 1RM (Determined, Estimated). If the patient achieves:

75 Repetitions = Continue with training, re-assess 1RM within 1-3 sessions. Reestablish new 20-30% range as strength improves.

60-74 Repetitions = Continue with training, but extend rest period between sets 3 and 4 to 45 seconds. Until 75 repetitions is completed.

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

• Early phase rehab- prevent muscle atrophy and promote healing. BFR training would consist of low intensity isometrics with or without electrical stimulation, easy mat exercises or even no exercise with only BFR. Researchers in the UK are beginning a study using BFR in the ICU to decrease muscle atrophy.

• 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.

• 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.
• 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.

Side Effects

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

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. 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.

Safety Implication

1. 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%.  The systematic review 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.

2. Muscle Damage

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.

3. Central Cardiac Responses

Research studies suggest 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.

5. 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 are:

• Nerve injury: Mechanical compression and neural ischemia play an important role. 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.