If you’re looking to improve your workout routine, especially if you’re focused on building muscle, you might love the trick Hailey Bieber uses. The bands wrapped around her thighs aren’t an aesthetic choice or one of the latest fashion trends. They’re BFR bands, used for a method known as Blood Flow Restriction, which involves deliberately restricting blood flow during exercise.

Although BFR may seem like the latest social media craze, its roots go back to 1960s Japan, where it was known as Kaatsu training. The method was invented by Dr. Yoshiaki Sato after he noticed numbness in his calves while sitting in the traditional Japanese position known as seiza for an extended period. He realised that deliberately and carefully reducing blood flow to the muscles could trigger cellular stress similar to that experienced when lifting heavy weights.

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Professional athletes have been using BFR for decades, and the method is also popular in physical therapy, particularly for muscle rehabilitation. Now, thanks to the growing popularity of biohacking methods, it’s making its way into gyms as well.

How Does BFR Work and What Is It Used For?

BFR is used on the limbs and involves placing specialised bands around the uppermost part of the arms (just below the shoulders) or legs (at the top of the thighs). The aim is to partially restrict venous blood flow (the return of blood from the muscles to the heart), while allowing arterial blood flow (which delivers oxygen to the muscles) to remain partially open. Creating these specific conditions of restricted blood flow causes oxygen to be depleted more quickly and metabolic by-products, such as lactic acid, to accumulate. The body interprets this as extremely demanding exercise and responds by activating metabolic pathways responsible for muscle growth and the release of growth hormone, even when you’re lifting very light weights.

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The Main Benefits of BFR Training:

Muscle growth with minimal resistance
Reduced strain on joints and tendons
Faster recovery from injuries

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Is BFR Safe for Everyone?

Before deciding to try this latest trend, it’s important to remember that BFR isn’t suitable or risk-free for everyone. When performed correctly and with the appropriate equipment, BFR is a safe method, but improper use carries the risk of tissue and nerve damage.

It is not recommended for people with high blood pressure, heart disease or vascular disorders, nor for pregnant women, people with diabetes or those with a history of thrombosis or venous problems. Additionally, if you’re new to weightlifting or fitness in general, BFR bands aren’t a good option.

The Most Common Mistakes When Using BFR Bands on Your Own:

Applying too much pressure: Completely blocking blood flow (occlusion) is dangerous. The goal is only partial restriction.
Using makeshift bands: Ordinary elastic bands or compression straps that don’t allow precise pressure adjustment significantly increase the risk of injury.
Wearing the bands for too long: The bands should remain on the limbs for no more than 10 to 20 minutes per workout.

If you’d like to experience the benefits of BFR training like Hailey Bieber, avoid makeshift bands and consult a physiotherapist or exercise specialist to learn how to apply the correct pressure and prevent unwanted complications.