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You may have heard that blood flow restriction (BFR) training, also known as KAATSU, is poised to become the next big fitness trend. It has certainly caught fire in some fitness circles, promising a way to build muscles stronger in a shorter amount of time.
And while it might sound like more fitness snake oil, according to a substantial amount of research, it does seem to deliver.
What is BFR training?
Originating in Japan, BFR training is a strategy that involves the use of wraps, or cuffs, placed around a limb during exercise. While there are some expensive, high-end pressure cuffs that you can buy to wrap your limbs, you can use any wrap that constricts and holds. In physical therapy, BFR is done by using a computerized tourniquet system, similar to a blood pressure cuff. This is supposed to safely restrict venous blood flow back to the heart from working muscles while still allowing arterial blood flow from heart to the muscles. Typically BFR is done during low-loading resistance training, but it can also be done while doing an aerobic activity like cycling or walking.
The idea behind the training method is that by decreasing oxygen through the restriction of venous blood flow, you can create a late metabolite build up such as lactic acid in the tissue. When that lactic acid is produced in the body, the pituitary gland secretes growth hormone in response. Ultimately, this works to create an increase in muscle hypertrophy (growth), muscle strength, and a slew of other benefits in as little as three weeks, although typically it takes four to six weeks. Meta-analysis shows that doing this training just 3 days a week.
“What we are learning via research is that by modifying blood flow to muscles during low loading exercise can improve an individual’s muscle strength, endurance, healing, and more,” explains Daniel Brown, PT, a Boulder, Colorado–based doctor of physical therapy. “The low loading allows us to strengthen without putting heavy and repetitive stress on the joints and muscles. This is what creates the magic! An easy way to look at it, as I often tell my patients, is ‘it provides the gains without the strains.’”
According to some research, lifting as little as 20% of an individual’s maximum strength can produce increases in muscle size and strength similar to that of traditional resistance training using nearer to 70% of the person’s maximum strength. Additionally, there is data that suggests that skeletal muscle and possibly bone may benefit from this training.
A meta-analysis looking at 11 studies on BFR training with a total of 238 subjects revealed that during both low-load resistance training and walking, the addition of BFR elicits significantly greater improvements in muscular strength. Additionally, muscle mass was increased when comparing walking with and without BFR. In a separate meta-analysis, a total of 400 participants were included from 19 different studies that looked at how muscle strength increased when both aerobic and resistance exercise is combined with BFR. When BFR was combined with aerobic exercise, a small improvement in mean strength between the experimental and control group was found. Mean improvement in strength was slightly larger when BFR was combined with resistance exercise.
How BFR Benefits Runners
So blood flow restriction clearly builds muscle, but how can this be of benefit to runners? After all, our goal isn’t to be able to lift the most.
“There are a plethora of significant benefits for runners, depending on what goal we are trying to achieve,” says Brown. “Dealing with runners specifically, there is evidence that using BFR during training appears to confer small but potentially worthwhile improvements in VO2max, peak running velocity, maximal oxygen uptake, and running economy.”
The most direct way that BFR may be able to benefit runners is by boosting the body’s ability to clear lactate and enhance strength endurance. In other words, helping you go faster longer. While doing BFR training, oxygen to the muscle is limited meaning that slow-twitch (Type I) muscle fibers, which require oxygen as fuel, are less active. Your body is forced to recruit the larger “fast twitch,” Type II muscle fibers.
Normally, to recruit those anaerobic muscle fibers you would need to perform exercises at a high intensity, or go long enough to fatigue Type I fibers. Not so when oxygen is limited! Essentially, when BFR is mixed with low-intensity exercise, you are able to create lactate production similar to high-intensity training (HIT) without the muscle damage and soreness. The primary aim of HIT is to increase the production of lactate so as to increase your body’s ability to clear the lactate and better utilize available oxygen.
There have been a few intriguing studies regarding BFR’s ability to potentially boost VO2max. In one 2010 study, a group that cycled with BFR for 15 minutes at 40% VO2max was compared to another group that biked for 45 minutes at 40% VO2max. Both groups did this exercise three times per week for a total of eight weeks. The group that paired the biking with BFR saw their VO2max jump up by 6.4% and an increase in exercise time to exhaustion while the control group did not.
Studies have also examined the effects of walking with BFR on endurance activities. One published in European Journal of Applied Physiology in 2010 had college basketball players walk for three minutes and rest one minute for five total rounds with BFR. They did this twice daily for six days per week, for two weeks. After what totaled to be 12 sessions, the BFR trained group had an 11.6% enhancement in their VO2max levels. Another more recent study done in 2016 found that BFR walk training improved VO2max levels by 3.5% in males ages 24 to 47 and lowered their 1.5 mile times.
Another exciting benefit of BFR training for runners that Brown notes is how it may be able to enhance the speed of recovery when injured. By forcing the body into an anaerobic state (when no oxygen is reaching the muscles) while using minimal weight, BFR creates or builds muscle without placing unnecessary stress on an injured area. If you have a muscle weakness or imbalance in an area that has resulted in injury, for example, this training can be used to treat that underlying problem. Furthermore, the growth hormone produced in BFR training serves a protective role for tendons and muscle collagen structures as it boosts collagen synthesis. This has implications important to rehab from injury as well as making BFR an intriguing tool for recovery in runners.
“Many Olympians and runners are already implementing BFR in their training and rehabilitation regimes, and I believe it will help us further push the limits in the running world,” says Brown.
While BFR training sounds relatively simple, Brown warns against buying a band online and try BFR training on your own without guidance from a physical therapist or other medical professional.
“Seeing a doctor of physical therapy who is experienced with Blood Flow Restriction training is the ideal first step,” says Brown. “They will be able to create an individualized plan based on a runner’s needs and goals, which is very important. BFR training is prescribed for diverse populations — everyone from professional athletes, wounded veterans, active adults, and the elderly — therefore having professional prescription will optimize the benefit for the individual.”
For as long as it’s been around, one reason it’s taken a while for BFR training to make it into the mainstream fitness culture is fear of muscle damage and blood clotting. Measurable muscle damage is rare with this exercise because of the low loads used and the short duration that it is applied, which is typically 5 to 10 minutes or less. The system responsible for blood clotting is also not activated when low load resistance exercise is combined with BFR. So this type of training is relatively safe.
However, certain individuals should be cautious before trying this out. Brown strongly recommends seeing a physical therapist before starting any training programs involving BFR. And definitely consult your primary care physician if you have underlying health conditions or medical history that could be a complicating factor. For example, those who are at an increased risk for blood clots should be careful with this exercise. Additionally, individuals who might have had lymph nodes removed shouldn’t use BFR on the affected limb.