If you haven’t heard of Kaatsu training before, you’re in for a treat. While still a novelty in the West, Kaatsu training was developed in Japan five decades ago. Ka means “additional” and atsu means “pressure.” An English layman’s term for the practice is “blood flow restriction training,” and involves performing strength training exercises while restricting blood flow to the extremity being worked.
A significant benefit of the method is that you can do strength exercises using just 30 to 50 percent of the weight you’d normally use while still reaping maximum benefits. In a way, you’re trading weight for repetitions, in that you’re using less weight but doing more reps — up to 20 or 30 repetitions opposed to the 10 or 12 you might normally do.
The cuffs or bands are just tight enough to allow arterial blood flow but not venous flow. This causes lactic acid and other waste products to build up, giving you the same benefit as heavy lifting without the dangers associated with heavy weights. For this reason, it’s a great strategy for the elderly and those who are recuperating from an injury.
Compelling evidence suggests that venous blood flow restriction dramatically increases muscle growth and strength by increasing growth hormone secretion, reducing myostatin and inducing cell swelling — all while circumventing the tissue damage that can occur with traditional high-intensity weight training.
Brief History of Kaatsu Training
The origins of Kaatsu training were detailed in a previous Outdoors Online article:1
"Kaatsu came about in 1966 when 18-year-old [Dr.] Yoshiaki Sato, now a doctor, noticed the intense ache in his calves after having assumed the traditional Japanese sitting position during a typically long Buddhist ceremony. It was an ache much like the one he experienced after lifting weights — an ache he realized had to do [with] the occultation of blood circulation.
Eureka! Using himself as a test subject, Sato spent the next several years perfecting a system of blood-flow moderation using bicycle tubes, ropes and straps. He later replaced the tubes with thin computer-controlled pneumatic bands. The idea was to apply pressure around the arms and legs while lifting a light load, safely impeding the flow of blood to exercising muscles.
Slowing this flow engorges the limbs with blood, expanding capillaries, engaging muscle fibers and raising lactic acid concentration. But — and here’s part of what makes Kaatsu unique — it fools the brain into thinking it’s being put through a vigorous workout."
It’s said blood flow restriction training can stimulate muscle growth and strength in about half the time, using about one-third of the weight, compared to standard weight training. By using much lighter weights, you’re also dramatically reducing your risk of muscle injury. In recent years, Kaatsu has caught on among professional soccer players, downhill skiers and American football players, including the Dallas Cowboys and the New England Patriots.
In the U.S., Dr. Jim Stray-Gundersen is a leading proponent and teacher of Kaatsu, earning the respect and admiration of athletes such as Olympic and World Cup ski champion Bode Miller — who credits Stray-Gundersen and the program with getting him back into world class form mere months after his back surgery — and other athletes who risked being sidelined by injuries.
Blood Flow Restriction Builds Muscle and Improves Performance
In the video above, Stray-Gundersen discusses Kaatsu and its benefits. If you’re intrigued by this technique, I highly recommend listening to the audio interview. The idea behind blood flow restriction training is to restrict the amount of venous blood flow your exercising muscle can get by tightening a cuff or band around the upper portion of the arm or leg being worked. This disrupts the homeostasis in the muscle, creating a metabolic crisis that has two primary effects:
A local effect — Reducing partial pressure of oxygen (Po2) and pH in the tissue stimulates protein synthesis. The cells will upregulate protein synthesis in an effort to improve homeostasis in the exercising muscle
A systemic effect — Your central nervous system also registers the crisis and sends out signals to compensate. Your autonomic nervous system reacts by increasing sympathetic tone, heart rate, ventilation and sweating (which is out of proportion to the actual work being done by the muscle); hormones involved in repair processes are also triggered, and human growth hormone, which facilitates protein synthesis.
Blood flow restriction also stimulates mTOR signaling2 and lowers your myostatin gene expression,3 thereby encouraging muscle growth4 (mTOR signals your cells to grow while myostatin, a protein produced by your muscle cells, inhibits myogenesis, blocking growth and differentiation).
One of the reasons blood flow restriction can compete with high-intensity weight training may be because it reduces myostatin to a greater degree than traditional high-intensity training (but with minimal muscle damage). Interestingly, muscle growth occurs both on the distal and proximal sides of the band; meaning, while you’re only restricting blood flow to your arms, your pecs are also affected and encouraged to increase in mass, in part due to the systemic hormone release.
So, in summary, blood flow restriction training is based on doing very light strength exercises (typically 30 to 50 percent of your one rep max) while venous return blood flow (the blood flow from your muscle to your heart) is being restricted or slowed, resulting in a low-effort exercise turning into “maximum exercise.” By forcing blood to remain inside your muscle longer than normal, you force more rapid muscle fatigue and muscle failure that sets into motion subsequent repair and regeneration processes.
Finding the Right Pressure
As for the amount of restriction required for optimal results, the answer is less clear-cut. You certainly do not want to restrict blood flow too much, as this could lead to severe bruising and/or dizziness. Were you to foolishly tourniquet your arm or leg to the point that all blood flow is completely cut off and leave it there for too long, nerve and muscle damage could result.
However, studies suggest such risks are relatively low.5 It’s simply too uncomfortable. If your limb starts tingling or turning red, blue or purple, you notice you’re losing feeling in it, and/or you cannot feel your pulse, your band is too tight and needs to be loosened. In other words, it’s fairly difficult to miss the signs of arterial occlusion or that your band is too tight.
As noted by Stray-Gundersen, “The real answer is, where you get fatigue and failure in the working muscle ends up being the right amount of restriction.” The proper wrapping and positioning of restriction bands is also addressed in the video above. When training, remember to use lighter weights — anywhere from 30 to 50 percent of what you’d normally use — and use a higher repetition rate instead.
Typical Training Protocol
Stray-Gundersen follows and recommends training protocols created by Sato, the original developer of Kaatsu. A typical training session would involve three sets, with repetitions ranging from 20 to 30 reps per set, using half or less of the weight you’d normally use. Rest periods between sets is typically short, say 30 seconds.
As a result, you’d end up doing upward of 90 repetitions of any given exercise, and the reason you want that many reps is because you need to work the muscle long enough to create the “metabolic crisis” conditions described earlier. It is that metabolic stimulus that drives the muscle adaptation and rapid growth.
That said, recommendations vary depending on who you listen to. According to the American College of Sports Medicine, you need to lift a weight that is at least 70 percent of your single rep max (1RM) in order to achieve muscular hypertrophy, arguing that anything below this intensity will produce insubstantial muscle growth.6
On the other hand, studies assessing low-intensity exercise in combination with blood flow restriction have shown muscle hypertrophy can occur even if you’re training at an intensity as low as 20 percent of 1RM, which is absolutely astounding. For most people this is lighter than a warmup and virtually guaranteed to not injure you.
Could Kaatsu Cause Deep Vein Thrombosis?
As for concerns that blood flow restriction training could lead to deep vein thrombosis, Stray-Gundersen dismisses such concerns, explaining:
"The short answer is, there are no concerns … [P]eople associated [blood flow restriction training] with putting a tourniquet on … creating a condition of venous and eventually arterial and capillary stasis of blood, which is a risk factor for deep venous thrombosis. In addition, there’s Virchow’s triad, where you need stasis, endothelial damage and … some other predisposing factor that’s [initiating the] clotting response. You don’t have those things with blood flow restriction training.
So as we were talking … about this idea of never occluding and really altering venous flow — going from almost a pulsatile venous flow, where your flow goes from very low levels to very high levels, and you distended the veins distal to the bands or belts …
[W]hat happens is, you’re backing up (as you have this model of a dam), you have this ‘lake’ being created that is extending the blood vessels … and you have muscle contraction that is clearing all of this stuff out at very high rates of flow. None of [this causes] any endothelial damage … So, you don’t have the requirements to cause these deep venous thromboses in the first place."
If anything, some researchers have actually found blood flow restriction training to have somewhat of a protective effect against deep vein thrombosis, assuming you’re doing it correctly.
“What you’re doing is you’re changing the venous flow in the deep system, essentially flushing out the system with every muscle action,” Stray-Gundersen explains, “so there’s really no concerns about thrombotic events … The big thing is, you never want to occlude the arterial side of the equation. As long as you don’t do that, you’re safe and, if anything, there’s a lower incidence of [deep vein thrombosis] …”
Other Possible but Rare Side Effects and Contraindications
Stray-Gundersen also addresses the issue of rhabdomyolysis, a condition that can trigger kidney failure or cardiac arrhythmia due to the release of intercellular contents from damaged muscle. It’s a rare but possible side effect of doing Kaatsu with too heavy a weight. It’s important to remember to drastically reduce the amount of weight you use and to focus on increasing repetitions. Contraindications, while rare, include the following:
Women who have had a mastectomy with or without radiation and/or an axillary node dissection. “Out of an abundance of precaution” he does not recommend doing blood flow restriction on that particular arm
People in hemodialysis who have arterial venous fistulas. Avoid doing blood flow restriction on the affected limb
Pregnant women. While women who have already done blood flow restriction for some time before getting pregnant may continue their training during pregnancy, it is not recommended to begin blood flow restriction during your pregnancy if you’ve never done it before
On a related side note, if you’re doing blood flow restriction training, you’d be well-advised to AVOID beta-alanine supplements. The reason for this is because beta-alanine improves homeostasis in the tissues, and in this case, you actually want to disrupt this homeostasis. Acutely, having high intracellular stores of beta-alanine may hinder or buffer that sought-after process.
Addressing Sarcopenia With Blood Flow Restriction Training
Sarcopenia, or age-related muscle loss, can actually begin at a relatively young age. By the time you’re 30, muscle decline may already have set in if you’ve neglected to take proactive steps to prevent it, and without intervention, you can lose an average of nearly 7 pounds (3 kilos) of muscle per decade.7
One of the factors involved in muscle maintenance is fast-twitch fiber activation, which is why high-intensity interval exercises (HIIT) are so valuable. Like HIIT, blood flow restriction training also activates fast-twitch fibers and triggers the release of human growth hormone, and may be particularly helpful for those who are getting up in age. It’s certainly easier to perform than HIIT if you’re frail and elderly.
According to Stray-Gundersen, blood flow restriction can go a long way toward restoring functional capacity in the elderly, even if they’re starting out barely able to get around. It’s actually used with great success in Japan to rehabilitate elderly individuals, allowing them to regain mobility and independence. Since you’re using such light weights, even those with poor strength can get a maximal workout with very low risk of injury. Sato goes so far as calling blood flow restriction “anti-aging medicine.”
Scandinavian studies cited by Stray-Gundersen have confirmed that blood flow restriction training activates stem cells and recruits and converts type 2X muscle fibers (fast-twitch glycolytic fibers) into 2A fibers (fast-twitch oxidative glycolytic fibers).8,9 Studies have also shown it helps stimulate bone turnover and repair.
Still unknown is whether tendons and ligaments also strengthen in response to blood flow restriction. Some trainers worry that muscle and bone mass may improve while tendons and ligaments remain weak in the absence of heavier loads.
Stray-Gundersen disagrees with this view, suggesting tendons and ligaments should be upregulated by the systemic hormonal cascade that is released, along with everything else — muscle, bone and blood vessels. That said, research is still too scarce to be able to definitively dismiss this concern.
Consider Adding Kaatsu to Your Workout Regimen
Overall, blood flow restriction training appears to be a tremendously useful strategy to add to your exercise regimen, especially if you’re getting older and/or struggle with declining muscle mass, or are trying to rehabilitate from an injury. The beauty of the technique is that it allows you to use very light weights at high repetition, giving you a high-intensity workout with minimal risks.
I am very impressed with the science and logic behind blood flow restriction training and have recently started incorporating it into my nitric oxide dumps, which works well, as there are enough repetitions to create the metabolic stress required to get the benefits. I only use it a few times a week and alternate between my arms and legs. When I use my legs I will do 20 walking lunges with 30 pound dumb bells (half of my max).
Elastic knee wraps are recommended because their elasticity and width allows you to comfortably wrap a larger surface area and reduces the risk of the band sliding down. Using thin rubber tubing or narrow nylon straps tend to increase the risk of excessive blood restriction as your muscles become engorged with blood. They can also reduce your flexibility.