As a physical therapist who follows many popular PTs and fitness professionals on social media, I’ve become aware of a new training phenomenon known as blood flow restriction training. Before diving into the research, I had many questions about whether or not this sort of training was effective or necessary for the patient population I see on a daily basis.
I consider myself a bit of a skeptic when it comes to new treatments that claim to produce better results than traditional physical therapy. However, this topic kept coming up in conversation with other PTs and fitness professionals. I figured I owed it to myself to take a look at the research and science behind blood flow restriction training and decide whether this was something I should try out.
What is blood flow restriction training?
Blood flow restriction training involves decreasing blood flow to working muscles in order to promote hypertrophy and prevent disuse atrophy of muscles. This treatment is typically used during exercise, but there is also evidence that you can prevent muscle atrophy by using these compression devices alone.
Are you convinced yet? Yeah, neither was I.
Blood flow restriction training involves the use of compression devices similar to a blood pressure cuff. The compression devices apply a pressure high enough to occlude 50-80% of blood flow to the muscles we wish to affect.
Science and theory
The most popular theory behind blood flow restriction training is that it leads to a local hypoxic event, which results in a greater accumulation of metabolites that regulate the anabolic response system during exercise. Consequently, we see an increase in anabolic growth factors, fast twitch fiber recruitment, muscle protein synthesis (via mTOR pathway), heat shock proteins (HSP), nitric oxide synthase-1 (NOS-1), and decreased expression of myostatin. Not only do we get an increase in the release of these anabolic response moderators, but we also limit the amount that can be removed due to the restriction in blood flow.
Are you still with me? Don’t get too caught up with the details just yet. Let’s first take a look at the research supporting these claims.
Study #1 - Blood flow restriction rehabilitation for extremity weakness: a case series (Hylden et al., 2015)
This study included 7 patients who underwent blood flow restriction training (BFRT) after their initial attempts at strength improvement were limited by the inability to successfully use traditional resistance training methods. All of these patients participated in BFRT 3 times per week for 2 weeks during PT sessions. The experimenters determined 1 repetition-maximum (1RM) without BFRT using a Biodex System 3 isokinetic dynamometer. The resistance used during BFRT was no more than 20% of each patient’s measured 1RM. Each patient completed four sets of knee extensions, leg press, and reverse leg press to failure with a 30-second rest interval between sets. The cuff pressure was inflated to 110 mm Hg.
All of the patients involved in the study demonstrated improvements in knee extension and flexion strength after 2 weeks of training with these methods. Interestingly enough, all of the patients involved in the study also saw improvement in overall average power.
Now I know what you are thinking - this is a case study, which is pretty low on the evidence pyramid we learned about in school. You may have even been taught to ignore these types of studies.
While I appreciate the fact that you respect the quality of the research, I want you to think about two important findings from the study: 1) The improvements were achieved using loads of only 20% 1RM on patients who were unable to gain strength from traditional methods. 2) The participants took part in 3 sessions per week for 2 weeks.
That’s only 6 sessions of treatment for patients who were previously unable to gain strength using traditional physical therapy techniques. Despite the low quality of evidence, these findings should pique our interest as physical therapists.
Study#2 - Blood flow restriction by low compressive force prevents disuse muscular weakness (Kubota et al., 2011)
This study included 11 healthy untrained males without a prior history of lower extremity injuries. Experimenters induced muscle weakness and atrophy by casting the participants’ ankles and instructing them to use crutches. Participants avoided weight bearing on the casted extremity for two weeks.
Subjects were randomly assigned to either a control group (no BFRT) or a group receiving BFRT intervention. The BFRT group received repetitive blood flow restriction with a compressive force of 50 mm Hg from a tourniquet applied on the proximal thigh. A set consisted of 5 minutes of applied blood flow restriction followed by 3 minutes of rest for 5 sets twice daily for 14 days.
The results of the study demonstrated that the percent decreases in knee extensor and flexor torques, as well as ankle plantarflexor torques (dorsiflexion was not tested in the study), were smaller in the BFRT group versus the control group.
Now, why are the results of this study important? 1) The study used a low pressure of only 50 mm Hg to mitigate muscle weakness from disuse. 2) Subjects did not participate in exercise of any sort. This second point here is the main reason I included this study in my article. The implications for physical therapy are profound, especially for those patients who cannot participate in high-intensity exercise.
Study #3 - Low-intensity blood flow restriction training: a meta-analysis (Loenneke, et al, 2011)
Finally, a piece of research you can sink your teeth into! Here we have an article at the top of the ever-heralded evidence pyramid! Sorry, I shall proceed…
This study set out to identify training variables that result in the greatest strength and hypertrophy outcomes with lower body low-intensity training using blood flow restriction. In order to be included in the meta-analysis, the primary focus of the study must have compared the effects of low-intensity endurance or resistance training alone to low-intensity exercise with some form of blood flow restriction. 11 articles met the inclusion criteria of the study.
This study found that regular low-intensity resistance training did not lead to increases in strength or hypertrophy. However, when low-intensity resistance training was combined with BFRT, significant increases were found. Greater improvements in strength and hypertrophy were found in the studies that used resistance training versus blood flow-restricted walking.
The optimal training frequency was found to be 2-3 days per week compared to 4-5 days per week, which the study attributed to overtraining. The study also found that muscular strength did not significantly increase until the 10-week time point, however hypertrophic gains were seen early on.
Finally, why are these results important? 1) Even though BFRT is a fairly new topic in sports medicine, we now have a gold standard study to refer to. Yes, I am saying that this article holds weight because of what we learned in our research classes in school about the evidence pyramid. Sometimes you have to accept a fact as simple as this if you are going to be a good consumer of the current research. 2) We no longer need to load our joints and muscles with high-intensity resistance in order to improve hypertrophy and strength.
This is the most powerful finding you could ask for in a study on BFRT. Just think about all those patients who cannot handle high-intensity exercise due to orthopedic or cardiac conditions. What about aging athletes who are trying to stay relevant in their sport and want to decrease the progression of arthritis and other joint damage?
Is it safe to use in the clinic?
Now that we’ve seen some decent research on blood flow restriction training (I still wouldn’t call the findings strong by any means), everyone’s next question should be about the safety of this type of training. We are physical therapists, so naturally, everything we do with our patients makes us liable for potential harm.
Before we begin our discussion on contraindications, consider the fact that pneumatic tourniquets are used in an estimated 15,000 surgical procedures worldwide to facilitate a bloodless surgical field with a high level of safety. Now please note that when using pneumatic tourniquets with blood flow restriction training, we are only occluding the vessel with a pressure high enough to decrease venous return, but low enough to maintain some arterial blood flow to the muscles.
Contraindications to blood flow restriction training include a history of DVT, pregnancy, varicose veins, and several other factors relating to the patient’s history of disease and inactivity. The most common side effects of blood flow restriction training are subcutaneous hemorrhage (bruising) and numbness, however these symptoms are often discovered at the beginning of a blood flow restriction training program and dissipate as an individual becomes accustomed to this training modality, as reported by a 2006 survey of Japanese facilities employing blood flow restriction training programs.
Before beginning this type of training with your patients, I would highly suggest that you receive training in blood flow restriction devices and techniques. Information on how to become certified in blood flow restriction training can be found at owensrecoveryscience.com.
I have intentionally left out a section with specific parameters to be used during blood flow restriction training because I want you to receive proper training before implementing this type of intervention. It is also important to note that the pressure in the blood flow restriction cuff will be different depending on each individual, so please do not try this technique on yourself or with your patients until you receive proper training.
After researching blood flow restriction training, I have come to the conclusion that this type of training could be of potential benefit to some of the patients I see on a daily basis. Some specific cases that come to mind are patients with moderate to severe osteoarthritis trying to avoid joint replacement, post-operative patients with a non-weight-bearing status, and patients with a history of recurrent ankle sprains due to poor lower extremity structure and weakness in the frontal plane.
Before I dove into the research, I had no idea what sort of applications a training technique like this could have. While it is still unclear to me whether a healthy athlete would benefit from blood flow restriction training versus resistance training with high intensity loads, there does seem to be some practical use of blood flow restriction training in a physical therapy clinic.
I challenge you to dig deeper into the research on blood flow restriction training. I want you to become more involved in research so that you can become the best clinician possible (evidence-based practice makes perfect!). We live in an age where people have unlimited access to information at their fingertips, so if one of your patients brings up the idea of blood flow restriction training, you should now be able to give them some information on the topic.
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Kang, Dong Yeon, Hyoung Su Kim, Kyung Soon Lee, and Young Mi Kim. "The Effects of Bodyweight-based Exercise with Blood Flow Restriction on Isokinetic Knee Muscular Function and Thigh Circumference in College Students." J Phys Ther Sci Journal of Physical Therapy Science 27.9 (2015): 2709-712. Web.
Kubota, Atsushi, Keishoku Sakuraba, Sadao Koh, Yuji Ogura, and Yoshifumi Tamura. "Blood Flow Restriction by Low Compressive Force Prevents Disuse Muscular Weakness." Journal of Science and Medicine in Sport 14.2 (2011): 95-99. Web.
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