Blood flow restriction training

What it is

A cuff at the top of the limb

A 2019 review by a group of BFR researchers sets out guidelines on how BFR is done and how safe it is¹. It defines BFR as partly limiting the blood flowing into working muscles through the arteries¹. At the same time, it fully blocks the blood leaving them through the veins¹. To do this, a cuff goes around the top of the arm or leg and is inflated¹. The cuff affects blood draining out of the limb more than blood flowing in¹.

The method traces back to Yoshiaki Sato in Japan, where it was called kaatsu training, meaning training with added pressure¹. Today it is more often called BFR training and uses an air-filled cuff system¹. It is used in three ways: during resistance exercise, during aerobic exercise, and without exercise¹.

How studies usually set it up

Loads are set against the one-repetition maximum (1RM), the heaviest load a person can lift once¹. A 2018 meta-analysis counted anything under 50% of 1RM as low load for BFR³.

Arterial occlusion pressure is the cuff pressure needed to stop blood flow in the limb¹. It depends on the cuff’s shape, width and length, the limb’s size and the person’s blood pressure¹. A wider cuff needs less pressure¹. The 2019 guidelines describe the method this way¹:

Load. The guidelines suggest 20 to 40% of 1RM, a range they say has produced muscle changes consistently¹.
Cuff pressure. The guidelines recommend basing pressure on arterial occlusion pressure, and report evidence for 40 to 80% of it¹.
Early studies. Most gave everyone one fixed pressure, from 50 to 300 mmHg (millimetres of mercury)¹.
Sets. A scheme often used in research is 75 repetitions over four sets of 30, 15, 15 and 15¹. Three to five sets taken to failure in the lifting phase are also common¹.

What it loads

Light weights, heavy metabolic demand

A review notes that mechanical tension is usually low in BFR resistance exercise, which uses under 50% of 1RM⁹. Squeezing the vessels above the muscle leaves it short of oxygen, called hypoxia¹. Blood pools in the limb’s capillaries (tiny blood vessels), often turning the skin red¹. Another review says the restriction lets by-products such as lactic acid build up in the fluid around muscle cells⁷.

A 2021 systematic review looked at light exercise with a cuff¹⁰. A systematic review is a study that searches for the research on a question in a set, checkable way. Against the same exercise without one, it describes more fatigue, a larger metabolic response and more muscle electrical activity¹⁰. In a meta-analysis of ten studies, light exercise at 60% of arterial occlusion pressure drew more muscle activity than at 40%¹⁰. Yet 80% did not differ from 40%¹⁰.

The library’s one exercise with BFR evidence is the tibialis raise¹¹. In one study, 17 healthy people did four sets of dorsiflexion, pulling the foot up toward the shin, against an elastic band¹¹. The shin muscle was more active over the last 20 lifts when blood flow was restricted¹¹. The same people rated those sessions more painful, difficult and uncomfortable¹¹.

The heart and blood vessels

The 2019 review says BFR affects heart and blood pressure measures during exercise, and even without exercise¹. The rise during exercise returns to resting levels 5 to 10 minutes after stopping¹. Studies that kept the cuff inflated between sets generally found higher heart rate and blood pressure than the same exercise without it¹. Letting the cuff down between sets appeared to reduce those differences¹.

In 19 randomised trials in healthy young people, adding a cuff to light exercise brought no greater short-term effects on the heart and blood vessels¹².
A 2018 meta-analysis looked at diastolic blood pressure, the lower number in a reading¹³. It was higher with BFR than with loads of 60% of 1RM or more¹³.
In people with high blood pressure, that meta-analysis found both numbers higher during BFR exercise¹³.
It also found blood pressure lower after BFR exercise¹³.
In 12 randomised trials of 378 older adults, light BFR training raised heart rate and blood pressure about as much as heavy training¹⁴.

How the body adapts

Muscle size and strength with light loads

A 2012 meta-analysis of lower-body studies compared light training with and without BFR². The effect size, a standard measure of how large a difference is, was 0.58 for strength and 0.39 for size with BFR². Without the cuff, the effect sizes were 0.00 and -0.01². Two to three sessions a week gave larger effects than four to five, and strength gains were linked to programme length².

The 2019 review reports gains in size and strength after as little as 1 to 3 weeks¹. It adds that part of the early rise in size may be oedema, swelling caused by fluid building up in the tissue¹.

Against heavy training: reviews disagree

For muscle size, a 2018 meta-analysis found similar gains with light BFR training and heavy training, whatever the cuff pressure or width³. For strength, reviews differ:

Review	Strength finding
2018 meta-analysis, heavy meaning over 65% of 1RM	Heavy training gave larger gains³
2020 meta-analysis of 310 healthy, habitually active adults aged 20 to 80	No difference⁴
2023 meta-analysis of 458 healthy adults	Heavy training gave slightly larger gains¹⁵

In the 2023 analysis, cuff pressure set for each person, raised over time, or applied on and off gave strength gains similar to heavy training¹⁵. One fixed pressure, or pressure held without a break, gave smaller gains¹⁵. A 2024 meta-analysis found that training status mattered⁵. Trained people may gain more strength and size with BFR than with heavy training; untrained people gained similar size but more strength with heavy training⁵.

Walking, cycling and rest

The 2019 review reports strength gains of 7 to 27% and size gains of 3 to 7% from low-intensity walking or cycling with BFR¹. A 2019 systematic review of 35 studies found favourable changes in neuromuscular (nerve and muscle) and metabolic measures with aerobic exercise and BFR¹⁶. It also found heart and blood vessel measures rose more than with exercise alone, and reported BFR as well tolerated¹⁶. Limited data suggest cuffs used on and off without exercise may offset muscle and strength loss during bed rest or immobilisation, keeping a limb still¹.

Tendon, bone and older adults

A 2024 meta-analysis of six studies in healthy adults compared tendon changes with light BFR and heavy training¹⁷. It found high-quality evidence of no long-term difference in cross-sectional area, a slice across the tendon, or stiffness, the force to stretch it¹⁷. A 2023 meta-analysis of 12 studies found light BFR training raised markers of bone health more than light training alone¹⁸. It was less effective than high-intensity training¹⁸.

In older adults, findings on strength differ^19,20. A 2019 meta-analysis of 238 older people found light BFR gave similar muscle growth to heavy training, but smaller strength gains¹⁹. A 2022 meta-analysis of 278 healthy adults aged 60 or over found no difference in strength from high-intensity training²⁰. In four studies of older adults, BFR training improved the timed up-and-go test, a 30-second chair stand and knee extension strength²¹.

After knee surgery

ACL reconstruction is surgery that rebuilds a torn anterior cruciate ligament (ACL), a ligament that crosses inside the knee²². In a randomised trial of 28 people after this surgery, one group did leg presses at 30% of 1RM with BFR, another at 70% without²². After 8 weeks, gains in strength and muscle thickness were similar, with no adverse events²². A 2024 meta-analysis of 8 trials found greater quadriceps volume with light BFR training than conventional training in the first 6 weeks after surgery²³.

A 2022 review of 11 studies of knee surgery found BFR after surgery can lead to significantly greater muscle size, measured as cross-sectional area²⁴. It found no difference in scores reported by the patients themselves²⁴. A 2024 review found just 5 studies after ACL injury and reconstruction: two favoured BFR for strength and size, and two suggested the opposite²⁵.

What studies found about safety

Muscle damage. In single sessions of light exercise, up to 5 sets to failure, the 2019 review found BFR did not appear to add muscle damage¹. One study found longer-lasting strength loss and swelling¹.
Rhabdomyolysis, a rapid breakdown of muscle tissue. There are isolated case reports of it with BFR, but the review concludes the evidence does not currently suggest a higher risk than ordinary exercise¹.
Clotting markers. Short-term studies, mostly in healthy men and all on the legs, found no significant rise in the clotting marker D-dimer¹. The 2019 review notes that many trials did not look directly for clots, though the research as a whole shows few clot-related adverse events¹.
Clot rates. A questionnaire of over 12,000 people in Japan reported a vein clot in 0.055% and a clot in the lungs in 0.008%¹. The 2019 review, which summarised it, notes the lung clots were not medically confirmed¹.
Adverse events. A 2020 review covered 322 people with muscle, bone or joint conditions⁶. In its randomised trials, adverse events were no more common with BFR than with exercise alone⁶.

Other findings point the other way: the 2020 review found rare events in three studies, including a clot in a deep arm vein and rhabdomyolysis⁶. In a survey of practitioners who had used BFR, the side effects reported most were delayed muscle soreness, numbness, fainting or dizziness, and bruising²⁶.

A 2015 narrative review, a summary written without a set search method, notes that reducing blood flow to working muscle engages the exercise pressor reflex⁷. This reflex helps drive the heart and blood vessel response to exercise⁷. The review raised concern because the reflex is exaggerated in high blood pressure, heart failure and peripheral artery disease (narrowed limb arteries)⁷. It argued even healthy people doing BFR may be at increased risk of heart and blood vessel events⁷.

A 2020 narrative review found that BFR may cause abnormal heart and blood vessel responses through the metaboreflex, a reflex set off in working muscle⁸. It found this more clearly in older people and people with heart and blood vessel disease⁸. It called BFR’s safety for the heart and blood vessels into question⁸.

Connections

BFR is used with resistance training and aerobic exercise, and in one study with elastic resistance bands^1,11. In muscle, tension is typically low, and metabolic stress is suggested as a main driver of growth⁹. Reviews have also measured tendon and bone^17,18. Related exercise page: tibialis raise¹¹.

Studies after surgery on the anterior cruciate ligament measured the quadriceps²³. A 2018 consensus statement on patellofemoral pain reported uncertainty about BFR training²⁷. Why BFR builds muscle is still not well defined, and a 2025 review lists this among open questions^9,28.