What is BFR (Blood Flow Restriction) Training?
Blood Flow Restriction (BFR) training, also known as “muscle blood flow restriction” in the Arab world, is a training method where a tight band is placed above a muscle, near the heart (e.g., between the biceps and shoulder to restrict blood flow to the biceps and triceps, or above the thigh to restrict blood flow to the leg muscles). The band restricts or blocks the return of blood from the muscle to the heart, trapping metabolic acids and metabolites in the muscle, which increases muscle hypertrophy.
This method is also known as Occlusion Training, Hypoxic Training, or Kaatsu in Japan.
The concept originated in Japan in the 1960s when Dr. Yoshiaki Sato, during a Buddhist ceremony, noticed a burning sensation in his calf muscle due to blood restriction. This sensation was similar to the feeling experienced during resistance training. He experimented by tying his muscles to simulate this effect and found an increase in muscle mass.
The restriction is applied by tightening the band enough to not significantly reduce arterial blood flow (blood entering the muscle) but to limit venous blood flow (blood leaving the muscle). This reduction in oxygen supply to the muscle (hence the term Hypoxic Training) shifts the focus to anaerobic fast-twitch type II muscle fibers and reduces the involvement of aerobic slow-twitch type I fibers. It also increases the buildup of metabolites like Myokines and Lactic Acid in the muscle, which causes the burning sensation in the last few reps of a set.
When lactic acid accumulates in the muscle, it triggers the release of growth hormone and activates the central nervous system (CNS) to recruit as many fast-twitch muscle fibers as possible. Lactic acid also increases fluid retention in muscle cells, causing them to swell (cell swelling). The muscle cells recognize this swelling as a threat and begin altering their structure, which stimulates protein synthesis.
In other words, BFR training maximizes metabolic stress on the muscle, one of the three mechanisms for muscle growth, alongside mechanical tension and muscle damage. Mechanical tension refers to lifting heavy weights through a full range of motion, while muscle damage involves causing microtears in muscle fibers, particularly during the eccentric phase of repetition.
What Weights Should You Use in BFR Training?
BFR training is typically done with very light weights, around 40% of your 1RM (the maximum weight you can lift for one repetition). For simplicity, consider using half the weight you would normally lift. For example, if you can lift 40kg for a bicep curl, you should use 20kg with the band.
Scientific studies have shown that the most effective muscle contractions for fast-twitch fibers occur when lifting around 40% of your 1RM. Another study found no significant difference in muscle contraction between lifting 40% and 80% of your 1RM during BFR training. However, lifting 80% of your 1RM reduces metabolic stress, which is why 40% of 1RM is generally recommended.
BFR training became popular in the field of physical therapy for rehabilitation purposes and is also beneficial for individuals with chronic joint injuries or older adults.
How to Apply the Band?
You can purchase a specialized BFR band or use a knee wrap above the muscle near the heart. For example, above the biceps, calves, or thighs.
The band should be tightened to a pressure level of 7 out of 10, where 1 represents no pressure and 10 represents maximum tightness, causing numbness in the extremities. Research has found that tightening the band too much (above 7) reduces arterial blood flow into the muscle, making the exercise less effective. The goal is to restrict venous blood flow leaving the muscle, not to block arterial blood flow entering the muscle.
If you tighten the band to a level lower than 7, there’s no problem; studies have shown that bands tightened to levels of 4 or 8 have the same effect on muscle growth and training effectiveness. Therefore, it’s better to err on the side of being too loose than too tight.
The band should cover an area of 5-9 cm. If using a knee wrap, don’t wrap it in a spiral fashion but instead layer it over itself to avoid exceeding 9 cm. If the band covers more than 13 cm, it can restrict arterial blood flow and reduce the effectiveness of the exercise.
How to Perform the Exercise?
BFR exercises involve high repetitions, typically 15-30 reps, since the weight used is light (40% of 1RM), with short rest periods. This allows for maximum accumulation of lactic acid.
The best approach is to perform supersets, such as combining biceps and triceps exercises or front and rear leg exercises (e.g., leg curls and leg extensions) at the end of your training session.
For example, regardless of your muscle-building or strength program, perform 3-4 supersets of isolation exercises for the biceps and triceps or 3-4 supersets for the front and rear thighs (e.g., leg presses and leg curls), with the prescribed weights and repetitions.
It’s recommended not to push to muscular failure until the final set of your workout to avoid overloading the central nervous system (CNS), which can reduce the effectiveness of your workout.
If your joints are healthy and you want to add this method to your program, it’s best to use it at the end of your workout. Additionally, since BFR training does not cause significant fatigue or impair recovery, it’s an excellent tool for deload weeks or lighter training phases.
Does BFR Only Work for Limbs?
I’ve discussed applying the band to the biceps, thighs, and calves, but what about other muscles like the chest, back, shoulders, and glutes?
Yes, all muscles can benefit from BFR when applied at the joints. Research has shown that applying the BFR band to the arms during a bench press with light weights increases chest activation by 16%. This is known as the Cross Transfer Effect, where the CNS compensates for fatigue in the arms by increasing chest activation to lift the weight.
Another explanation is that your blood becomes rich in metabolites and growth factors, benefiting all the muscles of your body.
A study also found that trainees who applied BFR to their arms after leg training experienced greater arm muscle growth.
Is BFR Training Safe?
A 2014 review found that long-term BFR training does not damage muscles or reduce strength or function. It also found that the muscle soreness (DOMS) caused by BFR is similar to the soreness from traditional resistance training without the band.
If you’re not accustomed to high-repetition training, it’s best to start with BFR exercises once or twice a week at most until your body adjusts.
There was a theory that BFR could cause narrowing or obstruction of blood flow in veins due to the band, but research has shown that after four weeks of BFR training, blood vessels expanded and blood flow increased more than with traditional resistance training.
BFR for Tendon Strength:
A December 2019 study divided volunteers into two groups: one performed heavy weight training (75% of 1RM) and progressively increased the weight to 85% of 1RM over four weeks, while the other performed BFR training at 20% of 1RM, progressively increasing to 35% over the same period.
Both groups saw the same increase in muscle strength and hypertrophy, as well as tendon thickness and strength! This indicates that BFR training is not only beneficial for muscles but also for tendon strength, making it an excellent tool for rehabilitation in physical therapy clinics.
