March 19, 2025, 3:07 pm | Read time: 7 minutes
Blood flow restriction, also known as kaatsu, is a training method in which the blood flow in the arms or legs is restricted in order to intensify the reaction in the muscle. FITBOOK explains how it works, whether it’s dangerous, and who shouldn’t do it.
If you look closely at the gym, you will spot them here and there: bands around the arms or legs of some strength athletes. They are put on to interrupt the blood flow — with the aim of supporting muscle development. But can squeezing the veins be healthy? FITBOOK spoke to experts about the blood flow restriction training (BFR) or Kaatsu training method.
Overview
What Is Blood Flow Restriction Training?
Translated, it means “training with restricted blood flow,” also known as occlusion training. The inventor Yoshiaki Sato, a doctor at the University of Tokyo, was already convinced as a young adult that the growth capacity of muscles could be significantly increased by depriving them of oxygen. It took him a few years to refine the technique and patent it in 1973 under the brand name Kaatsu. Sato also developed special Kaatsu bands to tie off the muscle and thus slow down the return of blood via the veins.
The traditional method of muscular training that Sato had in mind is now also used by amateurs on their own. However, they do not always invest in the expensive equipment provided. It is becoming increasingly common to see gym-goers tying off their upper arms or thighs with improvised cuffs, adhesive tape, or cords. That doesn’t look entirely safe.
Blood Clamping to Build Muscle — Dangerous or Effective?
Numerous studies have now confirmed that it actually works — as Priv.-Doz. Dr. Axel Preßler, a specialist in cardiology, internal medicine, and sports medicine at the Marianowicz Medizin Medical Center in Munich, tells us. In an interview with FITBOOK, he reveals that a wealth of data suggests that a temporary oxygen deficiency leads to an increased occurrence of growth hormones and insulin-like growth factors. “Good results have already been achieved with this method of muscular training in rehabilitative medicine.”
According to the expert, this is a positive reaction to an emergency situation. If the muscle is deprived of something, this leads to an increased stimulus to build up structures in order to be fully supplied again. Something similar is also known from other areas of sport, such as altitude training. “At a level with little oxygen, the body adapts by producing more red blood cells,” explains Dr. Preßler. “These ensure that the available oxygen is transported to the most important places: the muscles.”
But cutting off the blood flow — is it perhaps better to do this under medical supervision? Dr. Preßler is not so strict. “There’s actually nothing to stop you from trying out blood flow restriction training, even without the help of a professional.” The method is “on the whole relatively well tolerated,” he assures us, and you can’t really harm yourself with it. If the clamp is too tight, there is a risk of minor bruising.
Who Should Avoid Blood Flow Restriction
However, there are also serious contraindications for which blood flow restriction training should be avoided. This is stated in the “Position paper on Blood Flow Restriction Training” published by the Federal Institute for Sports Science. People with a genetic predisposition — such as weak veins, a predisposition to thrombosis, heart problems, or muscle diseases — are advised against it. BFR is also not suitable for high blood pressure patients.
How Blood Flow Restriction Training Works
The bandage is applied close to the muscle origin and without muscle tension. The aim is not to stop the entire blood flow, explains Dr. Preßler, but only the return flow via the veins. This means that the blood should flow in but not back out. “The muscle needs blood to be able to work; otherwise, permanent muscle damage could occur.” You can quickly see for yourself whether the fit is right. If the corresponding arm or leg starts to tingle after just a minute or less, the band is too tight; if the veins do not show at all, it is too loose. A more reliable check would be possible with a blood pressure cuff, but only very few people have one. A pressure of around 140 mmHg is considered ideal. “A good guide value is whether you can still feel a pulse at the wrist,” advises Dr. Preßler. “This shows that the blood is still rushing in.”
The training itself should be completed at 20 to 30 percent of maximum strength and should never last longer than an hour, which would definitely be too long, according to Dr. Preßler. The doctor recommends around three to four sets of 15 repetitions. If the tied muscle starts to tingle after about five minutes, this is normal. In this case, you don’t have to stop abruptly. “But you shouldn’t endure the feeling for much longer than a minute or two and then release the band.” Kaatsu is characterized by the use of relatively light weights. It is also not recommended to use heavier weights driven by over-commitment. “In that case, the muscle would quickly become undersupplied, which would have a negative effect on the metabolism. You would no longer benefit from the situation.”
Experts Give the Green Light
Professor Dr. Stephan Geisler, Professor of Fitness & Health Management at the IST University of Applied Sciences in Düsseldorf, has also had positive personal experiences with occlusion training. He first came into contact with it many years ago when he read a study report on the subject. He was quickly convinced by the theories presented. It has also proven its worth to him. He takes a closer look at the topic on his YouTube channel, Fitnessprofessor:
What Happens in the Body During Occlusion Training
As the fitness professor explains, there are two types of muscle fibers: the red ones, which contract more slowly, and the faster white ones. In order to stimulate the growth of the latter, “or maximum strength,” fast movements or intensive training with heavy weights are usually the best option; accordingly, these muscle fibers are particularly well developed in sprinters, for example. However, they are also said to react well to low-oxygen environments — he had read this before, and it was confirmed in several studies on BFR training. Prof. Dr. Geisler himself conducted research on blood flow restriction during strength training for the calves with colleagues. The analysis showed that low-intensity calf muscle training with blood flow restriction leads to similar functional and structural adaptations of the muscles as conventional strength training with low loads.
However, even the fitness professional Kaatsu does not consider it to be completely risk-free. He would, therefore, not recommend carrying out blood flow restriction training without professional supervision. “It’s difficult for amateurs to find out how tight they can put the bandages on,” says the professional. There are always those who overdo it, and — if the extremities are tied too tightly over a longer period of time or the restraints are not loosened — this can lead to damage to the tissue. Professor Geisler reports the case of a man who came to hospital with acute kidney failure. He had tied his legs with cable ties for hours.
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Conclusion
To summarize, occlusion training (or BFR or Kaatsu) is a good thing for experienced athletes without health contraindications — provided you do it correctly.