Exercise Smarter With Blood Flow Restriction Training
What if there was a way to exercise with lower weights and get the same muscular and aerobic benefits as a heavy session? Or a way to recover faster from injury while avoiding stress and potential injury to your joints?
When you exercise, the body undergoes stress and adapts to the demands placed on it. If you could heighten these stress signals you could compensate by lifting less weight. It sounds far-fetched but blood flow restriction (BFR) training has been shown to do just that, with enhanced muscle growth and strength using loads as low as 20% of a person's one-repetition maximum.
What is blood flood restriction training?
Blood flow restriction (BFR) training is placing a cuff on a limb and restricting some portion of blood flow to and from the muscle, like a tourniquet. Since the ability of the blood to escape the limb is dramatically reduced, the muscles have less oxygen to work with, cellular swelling increases, and metabolic stress occurs.
As a result, BFR creates a more stressful physiological environment and stimulates physical adaptation. A cascade of benefits occurs: increased growth hormone, muscle hypertrophy, muscle strength, muscle glycogen, rate of lactate clearance, recruitment of type-2 muscle fibers, capillary density, and VO₂ max.
BFR training can be viewed as an intensity modulator, a way to make exercise more challenging to the body. As such, it is not appropriate for everyone, and there are specific risks and contraindications, but it can be a part of most people's exercise toolkit.
BFR training makes more sense once you see it in action. Here's a demonstration using the Smart Cuffs product described at the bottom of this article.
How is BFR applied?
There are two types of BFR cuffs on the market: the cheap kinds that work like a belt to fasten around your limb and the more professional products that can be inflated to a specific pressure. Anecdotally, the cheap bands work, and I've noticed results myself, but they won't be as effective as pressure-controlled cuffs.
In the professional setting, a cuff with an internal air bladder is used, similar to a blood pressure cuff that is used at a doctor's office. The cuff is usually inflated to a certain percent of your limb occlusion pressure (LOP), which is the minimum amount of pressure required to stop blood flow to and from the limb. This varies from person to person and must be measured before training begins.
There's another BFR protocol called KAATSU that has its own methodology and will be discussed in a separate section below.
BFR cuff placement is at the top of each limb, either at the proximal portion of the humerus (between the bicep and deltoid) or at the proximal portion of the femur (top of the thigh). It's not typically recommended to apply cuffs to all four limbs at the same time, but rather to occlude a single limb at a time or both the upper or lower limbs.
How is limb occlusion pressure calculated?
Limb occlusion pressure (LOP) is determined either with a handheld ultrasound device called a doppler or by an automated device with pressure sensors.
To manually calculate LOP, the BFR cuffs are applied to a limb and the pressure is increased until a pulse is no longer heard on the doppler. For example, on the arm, the cuff would be applied and the pulse would be measured at the radial artery on the wrist until it is no longer heard. For the leg, the posterior tibial artery at the ankle can be used.
After the LOP is calculated for that limb, some percentage can be used during exercise, say 80% occlusion. This allows personalized pressure for each individual and eliminates the need to account for cuff width, limb size, or blood pressure.
The goal during exercise is usually to occlude venous (return) blood flow from the limb while allowing some portion of arterial blood into the limb. To do this, lower extremities need much higher LOP than upper extremities do. One leading company recommends a starting pressure of 80% occlusion for the lower limbs and 50% for the upper.
The science behind BFR
According to the science, the main benefits to BFR appear to be in muscle mass and aerobic performance, and not as much in muscle strength, although strength gains do occur and at a lower weight load. Differences in results exist between young and old, and trained and untrained individuals.
It is believed that several main stress signals are heightened during BFR training which lead to physical adaptation:
- Less oxygen – Less oxygen delivery to the muscles is caused by the occlusion of blood flow to the limb. This dependence on anaerobic metabolism and disturbed oxygen delivery during BFR training may stimulate adaptations that lead to greater anaerobic capacity. Increases in muscle glycogen stores, lactate clearance ability, and increased VO₂ max have all been observed. Oxygen deficiency is also known to increase the recruitment of fast-twitch (type II) muscle fibers to generate force and strength adaptations, which may explain the increases in muscle strength caused by BFR training.
- Less metabolite clearance – Less metabolite clearance from the limb due to the lack of blood flow has been suggested to increase toxicity and metabolite accumulation within the working limb, leading to muscular adaptations. Increases have been observed to muscle buffering capacity, which is the ability of muscles to neutralize the metabolites that accumulate in them during high-intensity exercise, thus delaying the onset of fatigue.
- Increased fluid stress – When a BFR cuff is depressurized, the blood flow that returns to the limb rushes in and causes fluid shear stress on the blood vessels. It's theorized that this stress may be a strong stimulator for the development of new blood vessels, which has been shown to improve aerobic power. KAATSU makes use of cycling between high and low pressures which could take advantage of this benefit of stress on the blood vessels.
What is KAATSU training?
KAATSU is a Japanese company that appears to be the original inventor of BFR training and has been making products since the 1960s. KAATSU is a Japanese word where KA (加) means “additional” and ATSU (圧) means “pressure”.
The latest KAATSU products use a portable electronic device to control the pressure in the cuffs and to run preset programs. One limitation of the product is that the devices don't use the standard mmHg (millimeters of mercury) units, but rather their proprietary unit called SKU (Standardized KAATSU Units). This makes it hard to compare KAATSU training to the scientific literature.
KAATSU is unique in that it uses a protocol called cycling. In the KAATSU cycle, the cuffs apply pressure for 20 seconds, followed by a release for 5 seconds. Pressure is incrementally increased during a 3-minute process to a safe and optimal pressure.
One potential issue with KAATSU is that the cuffs are relatively thin and require higher pressures. It is known in the scientific literature that wide cuffs require significantly less pressure to achieve limb occlusion pressure (LOP). In one study, they were unable to reach LOP with the KAATSU bands and calculated it to be greater than 500 mmHg.
What is BFR best used for?
BFR has a wide range of applications but is especially suited for when high weight loads are not desired or appropriate, such as in the cause of injury, age, or physical limitations. However, even in highly trained individuals, BFR has been shown to cause beneficial adaptations.
Here are some example use cases for BFR training:
- Injury rehabilitation – BFR training has been shown to enhance muscle mass and strength using loads as low as 20–50% of a subject's one-repetition maximum. This enables people who are rehabilitating to get more results in less time. Unlike traditional rehab, BFR can be used for static cellular swelling directly after surgery, taking advantage of some of the physiological stress signals mentioned above.
- Aging population – BFR is an effective approach for increasing muscle strength across a wide spectrum of age and physical capacity, although it's particularly beneficial for those individuals with physical limitations who can't engage in high-load resistance training. The addition of BFR to light resistance training or walking is an effective exercise alternative for older populations, for whom a traditional high-load training program might be contraindicated due to chronic diseases or high mechanical stress to bones and joints.
- Muscle mass / hypertrophy – One meta-analysis concluded that BFR combined with low-weight resistance training induced comparable gains in muscle mass when compared to high-load resistance training without BFR.
- Walking – Normally, walking does not cause physical adaptations in healthy adults. A meta-analysis concluded that during both low-load training and walking, the addition of BFR elicits significantly greater improvements in muscular strength. Muscle mass was also increased when comparing walking with and without BFR. In comparison with high-load training, low-load training combined with BFR promotes similar muscle volume but lower strength gains. Another study of college basketball players showed that walking with BFR at pressures of 140–200 mmHg significantly increases VO₂ and VE max.
- Aerobic performance – At a given exercise intensity, BFR exercise has been suggested to reduce arterial blood flow and increase venous pooling within the limb, decreasing stroke volume and causing a subsequent increase in heart rate, thus placing increased mechanical stress on the heart and driving cardiovascular adaptions. BFR aerobic exercise at light intensities has been shown to cause improvements in both aerobic fitness and aerobic performance in young adults when using higher occlusion pressures (130 mmHg or greater). Conversely, BFR combined with aerobic exercise seems to strictly enhance aerobic performance in older adults, without impacting physiological measures of aerobic fitness.
- VO₂ max & capillary density – In trained individuals, the combination of sprint interval training and BFR (pressure of 130 mmHg) was shown to stimulate large improvements in VO2 max when compared with sprint interval training alone. The authors hypothesized that training with the implementation of BFR during the recovery periods may cause an increase in capillary density within the muscle tissue, leading to a subsequent increase in VO2 max.
Are there systemic benefits to BFR training?
A common question is are there benefits above the cuff? In other words, if you place cuffs on your arms and do a bench press, does your chest benefit?
According to science, yes. This exact scenario was studied: subjects bench pressed at 30% of their one-repetition max with BFR cuffs on their arms. Only the group that used BFR saw increases in their one-rep max weight and thickness of their tricep and pectoral muscles.
The observed effects of BFR include increases in heart rate and intensified systemic hormone production. The increased heart rate places mechanical stress on the heart and could lead to greater cardiovascular health. The increased growth hormone could trigger a larger adaptation response, even for muscles that weren't specifically targeted by BFR.
Risks and contraindications of BFR
BFR is not for everyone. The most at-risk populations are those that wouldn't be in the gym anyway. So if you haven't been cleared to exercise by your doctor I wouldn't recommend this exercise modality. Also, those with weaker cardiovascular systems may want to proceed with caution.
Here are some risks that have been discussed in the scientific literature:
- Clot / thrombosis – The risk of a blood clot caused by BFR is likely similar to that of traditional high-intensity resistance exercise in healthy, active adults. The collective literature suggests that a proper prescription of BFR in the context of the three main triggers (stasis, endothelial injury, and alterations in blood constituents) would not heighten the risk of developing blood clot.
- Rhabdomyolysis – Rhabdomyolysis is the breakdown of muscle tissue that leads to the release of muscle fiber contents into the blood, which are harmful and can cause damage to the kidneys. There have been a handful of reported cases of exertional rhabdomyolysis resulting from strenuous physical exercise with BFR. BFR can place high metabolic stress on skeletal muscle and any exercise protocols should progress gradually.
- Blood pressure issues – A meta-analysis concluded that although resistance exercise with BFR resulted in lower blood pressure after exercise than normal, higher systolic and diastolic values were observed during exercise, especially in hypertensive individuals. Thus, exercise with BFR should be prescribed with caution when blood pressure control is necessary during exercise.
- Injury to a nerve – Tourniquets can cause permanent nerve damage if applied to the wrong spot, kept on too long, or used at too high a pressure. This is why a standardized placement is crucial, the bands should not be left on more than 10-20 minutes, and why you should use wider cuffs because they require less pressure.
Best BFR products to buy
The inexpensive straps
The biggest issue with these low-cost BFR cuffs is that you have to guess how much pressure you're using. Without measuring LOP and inflating to a certain percentage of that, you don't know how much blood flow you're occluding.
Regardless of whether you get the more expensive pressurized cuffs or not, it's recommended to use wide cuffs as they require lower pressures. There are one-inch bands on the market but I recommend getting at least a two-inch size to avoid potential injury.
Keep in mind that the bands will have to be tighter on the legs to get the same amount of blood occlusion, but use common sense and don't exceed a 7/10 on the pain scale.
The professional devices
There's a night-and-day difference between the cheap and professional cuffs. These products hold their pressure very well and the precision of a certain pressure during training can be felt.
The two options below are the only companies making professional-grade consumer products at the time of this article's publication:
- Smart Cuffs – A set of two cuffs and a pressure meter is $350. These are one of the only two FDA-approved products on the market. To reduce the amount of pressure needed, the cuffs are wide. This company also just released a new version that included an automated unit to control the pressure and will retail for $300 with a set of cuffs.
- KAATSU – The least expensive unit is $900. This includes four cuffs (arms and legs) plus the control device. KAATSU is unique in that they offer cycling protocols where the pressure is increased and decreased at certain intervals. Also, the straps are elastic so they stretch with exercise.
There's one other FDA-approved product called the Delfi Personal Tourniquet System. However, a single-cuff system costs roughly $5000 and purchase requires an active medical license and completion of a certification course. Unfortunately, this makes them out of reach for most consumers.
The question is no longer whether BFR training works, but rather what are the best populations to make use of it and what are the specific risks or contraindications.
According to the American Physical Therapy Association, BFR training is part of the professional scope of practice for physical therapists. While still a niche practice, I predict it will continually become more mainstream as people learn about the benefits it offers.