What is Blood Flow Restriction Training and Can it Aid in the Rehabilitation Process?There are two leading concepts that lead to muscular hypertrophy and increased strength: the cellular environment and the overload principle. The overload principle states that in order to increase muscular strength, one must stress a muscle beyond its limit in order to stimulate this muscular growth. As a result of the overload, the muscle unit develops microtears, which stimulate the protein synthesis cascade to make the muscle return and grow stronger. The second concept creates an environment that can stimulate the same muscular response. When a muscle comes under stress, it produces lactate as a byproduct of this increased work. As this lactate accumulates, it promotes an anabolic environment that induces a hormonal response that assists the body in repairing the muscle. In conventional training, this is done by increasing resistance over a period of time that stimulates these two cascades. Blood Flow Restriction Training (or BFR Training) is an alternative method of inducing an anabolic environment by manipulating circulation with the application of a pneumatic tourniquet. The pressure in the cuff of the tourniquet alters circulation, restricting venous return while allowing for normal arterial blood flow. With exercise, this decreases the lactate re-uptake and increases its accumulation in the cells, which decreases the time to muscle fatigue. As a result, the muscle stimulates the same hormonal response seen in high resistance training, without excessive micro-tearing. This is particularly useful for patients with injuries or other training limitations, enabling them to train with less resistance and achieve comparable muscular hypertrophy.
Background PhysiologyIn order to get a full appreciation of what is happening with BFR training, let us take a look at a cellular level. BFR has been found to affect two specific hormones; growth hormone (GH) and Insulin Growth Factor – 1 (IGF-1). GH is a hormone that promotes metabolism, protein synthesis and the increases the of IGF-1.1 IGF-1 is a gene that stimulates mTOR signaling (Akt) which stimulates skeletal muscle hypertrophy. This is a pathway that integrates intracellular and extracellular stimuli, which promotes either an anabolic or catabolic response.1 This process can be described as a metabolic “roller coaster” that can switch a cell from an anabolic or catabolic state, but in the case of IGF-1, it begins an anabolic response. Through this cascade, hypertrophic genes are further upregulated. Man, all this just for the growth of skeletal muscle. Research has shown that high-intensity interval training (HIIT) significantly increases serum GH and IGF-1, which is one of the reasons it is widely used for muscle growth. BFR achieves similar levels of GH when compared to HIIT following exercise, at a lower intensity. In addition, IGF-1 is significantly increased two weeks following BFR training in comparison to low or high-intensity exercise.2 Following the mTOR signaling cascade, there is also downregulation of a specific gene called myostatin.3 Myostatin is a negative regulator of skeletal muscle, meaning it decreases muscular growth. When present, Myostatin reduces the amount of muscle tissue growth that is possible by decreasing the number of tissue fibers and, consequently, the size of the muscle as a whole. The downregulation of Myostatin has the opposite effect; therefore, less muscle wasting occurs with BRF training.4 One study followed participants in a 12-week BFP program and showed that the expression of Myostatin decreased by 25%, resulting in an increase in the hypertrophy and the promotion of the mTOR signaling pathway.5 It is crazy that all of these events are happening in your body but this is only the surface physiological mechanisms that are happening when you are performing BFR.
A Comparative Analysis of BFR and Resistance Training Methods:When comparing the effectiveness and benefits of each type of training, there are a few specific factors to consider: training intensity, hormone response, and training response. The ACSM Exercise Guidelines states that High-Intensity Resistance Training should be performed at >67% of your 1-RM. The goal of performing exercise at this intensity is to overload the muscle unit, forcing it to contract at max effort. When a muscle contracts at this intensity, it fatigues through lactate accumulation and develops microtears which promote protein synthesis. Additionally, protein synthesis can only occur during the down-regulation of myostatin, which allows for a systemic release of human growth hormones. Training with this intensity takes 8-12 weeks to see muscle hypertrophy or strength gains. One notable benefit of BFR is the ability to train at a lower intensity, <35% of 1-RM, while also facilitating a similar anaerobic environment needed for the stimulation of protein synthesis and muscle hypertrophy. Without the micro-tearing associated with heavy resistance training, the body is better able to facilitate protein synthesis, leading to quicker muscular hypertrophy. BFR training at a lower intensity essentially allows an individual to achieve the same hypertrophic muscular response without the joint or connective tissue stress.
Safe Use, Risks, and Vulnerable Populations:One question surrounding the clinical application of BFR remains to be its safety within the clinical setting. Research suggests there is minimal risk of adverse effects including venous thrombosis and other cardiorespiratory if performed under the correct circumstances. To summarize the safety of BFR in clinical populations, we have highlights a patient survey of 12,262 patients. The following is a summary of the results:
- Nakajima et. al (2006)6
- Venous Thrombosis (n=7, 0.055%)
- Pulmonary Embolism (n=1, 0.008%)
- Rhabdomyolysis (n=1, 0.008%)
- 2 other cases reported in the literature in cases where subjects were dehydrated, wore cuff for greater than 1 hour, and heavy resistance training
- The effects of BRF have not been tested on certain vulnerable populations such as pregnant women, due to Institutional Review Board Restrictions. Therefore, the effects are unknown and warrants being considered a relative contraindication.
- Absolute Contraindications for use include:
- Patient with a history of DVT
- High blood pressure >180/100 mmHg
- Acute illness
- Any other unstable heart conditions due to the effect that partial restriction of the venous return has on the cardiovascular system.
BFR Training Set-up and SchemesThe key to avoiding and preventing any of the above adverse effects is to adhere to all set-up and safety guidelines. The two most important aspects to consider are the cuff placement and pressure within the cuffs. Whether performing Upper or Lower extremity training, the cuffs should be placed as proximally as possible regardless of target muscles. The purpose of this is to reduce the likelihood of compressing arteries and neurovascular structures. For example, areas such as the axilla or gluteal fold are deeper to the veins we aim to target. The second part is making sure that the clinician makes an individualized pressure prescription each session. The clinician does this by locating the Limb Occlusion Pressure (LOP) of each target limb with the use of a Doppler Ultrasound on the radial or dorsal pedal pulse. The Limb Occlusion pressure varies from patient to patient and even within the same individual between sessions. Below is an example of the set-up for finding the LOP. Discontinuation Protocol: The clinician must look for certain signs and symptoms in their client. If any of the following presents, promptly discontinue and allow the patient to rest under supervision:7,8
- Numbness and tingling
- Severe discomfort
BFR Training Principles
- Training Intensity: 10-35% 1 RM (BODYWEIGHT)
- Recommended Rep Scheme: 4 sets (30,15,15,15)
- Rest between sets: 60 seconds
- Total time of Training: 6-10 minutes
- Reperfusion time following BFR Training: 3-5 minutes
- Training Frequency: 2-3x/week
Patient PopulationAs we have previously mentioned, patient populations with activity limitation are ideal candidates for BFR training in the rehabilitation setting. The following is an overview of potential target populations:
- Quad atrophy is the most significant limitation post-surgery in getting patients back to the previous level of functioning.
- Decreased Knee Extensor (Quad) Disuse Atrophy to 8% at 2-weeks postoperatively compared to 35% Non-BFR training group.
- Increase in Cross-sectional area at 4 weeks and 6 month
- Summary: Significant increase in muscular strength & cross-sectional area with BFR compared to the matched protocol without BFR (p<0.05) both short and long-term follow-ups.
- Decreased anterior knee pain at higher levels of intensity
- NPRS decrease of 52%
- Improved Strength
- 72% increase quad strength in 6 weeks
- Improved Functional Outcomes
- 43% decreased in functional testing TUG
- Decreased anterior knee pain at higher levels of intensity
- Elderly Patients 5,13
- Increased Muscular Strength
- ↑11% and 7%–16% in isometric and isokinetic knee extension and flexion torques, respectively
- Improved Functioning
- Significant improvement in TUG and 30-second sit to stand over 6 weeks
- Increased Muscle Hypertrophy
- ↑5.8 % and 5.1% in CSA of the thigh and lower leg, Respectively
- ↑ 17.6% and 17.4% in CSA of elbow flexors and extensors, respectively
- No evidence of a higher risk of use
- No significant changes in hemodynamic parameters or muscle damage markers (CK)
- Increased Muscular Strength
- NWB (TKA/THA/Fracture)9,10
- Improved Functioning
- Decreased time to upgrade WBing status
- Reduction in Disuse Atrophy
- A similar decrease in quad atrophy as ACL protocols
- Edema Reduction
- Creates a pressure gradient
- Improved Functioning
- Needs more research
- RTC Tendinopathy
- Chronic Pain & Adhesive capsulitis- Subjectively has decreased pain and can result in increased exercise/ROM tolerance
Closing ThoughtsAppropriate application of new technology is an important part of improving practice as physical therapists and personal trainers. BFR training is a tool that may aid training for patients who are unable to perform higher level activities. For these populations, it can make a big impact in decreasing the effects of immobilization or atrophy over time. However, BFR is not equivalent to other forms of training that involve challenges to the neuromuscular system. Therefore, BFR should not always replace other methods but does provide a novel piece of the puzzle for specific patient populations. References:
- Kim E, Gregg LD, Kim L, Sherk VD, Bemben MG, Bemben DA. Hormone responses to an acute bout of low-intensity blood flow restricted resistance exercise in college-aged females. J Sports Sci Med. 2014;13(1):91-6. Published 2014 Jan 20.
- Abe T, Sakamaki M, Fujita S, Ozaki H, Sugaya M, Sato Y, Nakajima T. Effects of low-intensity walk training with restricted leg blood flow on muscle strength and aerobic capacity in older adults. J Geriatr Phys Ther 33: 34–40, 2010.
- Hsu PP, Kang SA, Rameseder J, et al. The mTOR-regulated phosphoproteome reveals a mechanism of mTORC1-mediated inhibition of growth factor signaling. Science. 2011;332(6035):1317-22.
- Carnac G, Vernus B, Bonnieu A. Myostatin in the pathophysiology of skeletal muscle. Curr Genomics. 2007;8(7):415-22.
- Santos AR, Neves MT, Gualano B, et al. Blood flow restricted resistance training attenuates myostatin gene expression in a patient with inclusion body myositis. Biol Sport. 2014;31(2):121-4.
- Nakajima T, Kurano M, Iida H, et al. Use and safety of KAATSU training: Results of a national survey. Int J KAATSU Train Res. 2006;2(1):5-13. doi:10.3806/ijktr.2.5.
- Umbel, J. D., Hoffman, R. L., Dearth, D. J., Chleboun, G. S., Manini, T. M., Clark, B. C. (2009). Delayed-onset muscle soreness induced by low-load blood flow-restricted exercise. Eur J Appl Physiol, 107(6), 687-695.
- Madarame, H., Sasaki, K., Ishii, N. (2010). Endocrine responses to upper- and lower-limb resistance exercises with blood flow restriction. Acta Physiol Hung, 97(2), 192-200.
- Joshua Slysz, Jack Stultz, Jamie F Burr. THE EFFICACY OF BLOOD FLOW RESTRICTED EXERCISE: A SYSTEMATIC REVIEW & META-ANALYSIS. J Sci Med Sport 2016 Aug 28;19(8):669-75. Epub 2015 Sep 28.
- Hughes L, Paton B, Rosenblatt B, Gissane C, Patterson SD. Blood flow restriction training in clinical musculoskeletal rehabilitation: A systematic review and meta-analysis. Br J Sports Med. 2017;51(13):1003-1011. doi:10.1136/bjsports-2016-097071.
- Ohta, Haruyasu, et al.Low-load resistance muscular training with moderate restriction of blood flow after anterior cruciate ligament reconstruction.” Acta Orthopaedica 74.1 (2003): 62-68.
- Takarada, Yudai & Takazawa, Haruo & Ishii, Naokata. (2000). Applications of vascular occlusion diminish disuse atrophy of knee extensor muscles. Medicine and science in sports and exercise. 32. 2035-9. 10.1097/00005768-200012000-00011.
- Clarkson Matthew John, Conway Louise, Warmington Stuart Anthony. Blood flow restriction walking and physical function in older adults: a randomized control trial.Journal of Science and Medicine in Sport http://dx.doi.org/10.1016/j.jsams.2017.04.012
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