You might have already heard of it, or perhaps seen someone in the gym doing it. Occluding their arm or leg with wraps before exercising with a (apparently) low weight. But despite the low weight, it seems as though the gym beast quickly reaches muscular failure. How? Well, this type of training is called Blood Flow Restriction, or KAATSU training. But is it really that effective in increasing muscle mass and strength?

What is KAATSU training?

KAATSU training (meaning ‘additional pressure’) is a training method that was developed in the late 1960’s by the Japanese scientist and bodybuilder dr. Yoshiaki Sato. KAATSU training has started to (again) receive a lot of attention in the past years as Blood Flow Restriction training (BFR). KAATSU/BFR is performed by reducing blood flowing towards and from an exercising muscle for a short period of time (usually max 5 minutes). Reducing muscle blood flow in this manner consequently reduces oxygen availability for a short period and is believed to create an environment within the muscle (also known as metabolic stress) that is similar to what the muscle experiences during a heavy weight exercise set. Training this way is suggested to strongly stimulate the muscle to adapt and to increase in mass and strength, despite the low weight and total training volume. Well, that’s the theory at least, but the question is, does it really work?

Does KAATSU training work?

A recent scientific article published in the scientific journal Medicine & Science in Sports and Exercise from the group of Prof. Luc van Loon from Maastricht University concluded that skeletal muscle protein synthesis (the process driving muscle growth) indeed increases when low-load resistance exercise is combined with BFR, compared to performing the same exercise (sets and reps) without BFR. Interestingly, a recent systematic review and meta-analysis published in the scientific journal Sports Medicine concluded that training with a low-load with BFR can be as effective in increasing skeletal muscle mass as training with heavy loads of 60-80% 1RM (one rep max). However, their analysis also suggested that when the primary goal is to increase muscle strength, that training with heavy loads is more effective. The authors from that paper concluded that this is most likely due to the greater stimulation of neuromuscular adaptations when training with heavy loads (and thus more similar to what is experienced when testing strength).

So, is KAATSU useful?

Well, if you are a gym beast that is used to exercising with heavy weights, is there a reason to consider BFR training? At this moment, there doesn’t seem to be a reason to include low-load BFR training if you are able to exercise with heavy weights (≥60% 1RM). Furthermore, BFR training with a weight that is greater than 40% 1RM also does not seem to be more effective than training without BFR to fatigue (both for gains and to reduce training volume). This is part of the reason that low-load BFR training is primarily applied when heavy-load resistance training is not possible, for example by physical therapists to treat rehabilitating athletes that are injured or following surgery.

What about periodizing heavy-load resistance exercise with low-load resistance training then? At the moment, there isn’t that much research to be sure how to effectively apply such an approach. However, don’t be alarmed if you are already doing something like this. A recent scientific article also published in Medicine & Science in Sports & Exercise assessed alternating heavy-load resistance training with low-load BFR training in elite Norwegian powerlifters. They split the powerlifters in two groups and had them perform a heavy-load front squat training program for 6.5 weeks, with one group performing low-load BFR front squat training for two of those 6.5 weeks.

"While the addition of low-load BFR training didn’t increase type II muscle growth, it did stimulate type I muscle growth to a greater extent in powerlifters."

What they saw was that periodization with low-load BFR training resulted in an increase in quadriceps muscle mass, while the group that only performed heavy-load front squats did not show an increase. The authors concluded that this difference was due to the fact that the two weeks of low-load BFR training also stimulated type I muscle fiber growth. Heavy-load resistance exercise, which is what powerlifters are more used to doing, primarily stimulates type II muscle fiber growth and has a smaller effect on type I fibers. So, while the addition of low-load BFR training didn’t increase type II muscle growth, it did stimulate type I muscle growth to a greater extent in powerlifters.

Conclusion

So, if you are still capable of gaining strength and mass from heavy-load resistance training, there doesn’t seem to be a reason to consider KAATSU/BFR training. KAATSU/BFR training does however seem to be extremely useful when injured or during rehabilitation. But based on the recent findings in powerlifters, you shouldn’t be surprised if you start seeing more of KAATSU/BFR in gyms.