<img style="display: block; margin-left: auto; margin-right: auto;" src="https://opedge.dev/wp-content/uploads/2021/01/2020-09blood.jpg" alt="" /> In recent years, the importance of muscular strength has been recognized as a critical piece to optimizing health, and research has highlighted leg strength as a strong predictor of all-cause mortality and an indicator of positive clinical outcomes.<sup>1,2,3</sup> Without the requisite strength to simply stand upright, moving efficiently and safely is difficult, and the comorbidities associated with physical inactivity are compounded. A solid foundation is required for all closed chain movement. Many people with amputations are severely detrained by the time they are ready to begin using their prostheses in therapy, so the beginning of physical therapy must be spent strengthening the patient's musculature to prepare for prosthesis use rather than for gait training and skill acquisition. Without the ability to bear weight through a limb, strengthening the muscle surrounding a joint is slow and difficult. Two factors are critical for strength and hypertrophy gains: mechanical tension and metabolic stress. These two components are interrelated, interreliant, and work through multiple pathways. Mechanical tension is active lengthening and shortening of the muscle tendon units. Metabolic stress is the physiological process that occurs as a response to fatigue, resulting in metabolite accumulation in the muscle cells. The effects of metabolic stress can be controlled by manipulating the intensity and the stimulus to effect different energy systems and pathways. Low-load resistance training will have a very different (reduced) effect on metabolic stress than high intensity interval training.<sup>6</sup> Older populations are volume sensitive and intensity dependent when it comes to resistance training, meaning that if they perform low load lifts for a high number or repetitions, they become increasingly sore. But what if I told you that we can elicit the metabolic response of high-intensity interval training by implementing a strictly low-load lifting program? New therapeutic approaches have been developed to optimize outcomes while accounting for the severely detrained patient population. Blood flow restriction (BFR) therapy involves restricting blood flow to a limb through the application of a specialized tourniquet system combined with low-load lifting to elicit a heightened state of metabolic stress, leading to statistically significant gains in strength and hypertrophy (muscle growth).<sup>5</sup> BFR is not a new concept. The model has been around for decades. Originally referred to as Kaatsu Training, BFR was first practiced in Japan by Yoshiaki Sato, MD, PhD, in the 1990s. In the early 2000s, the method gained interest in the weightlifting and sports science communities and was referred to as occlusion or tourniquet training.<sup>5</sup> BFR has since become more mainstream, being used in professional sports locker rooms, physical therapy offices, and research labs. The movement has been captained by Johnny Owens, MPT, owner of Owens Recovery Science. Owens is the former chief of human performance optimization at the Center for the Intrepid, part of the Department of Orthopedics and Rehabilitation at the San Antonio Military Medical Center. At first glance, BFR sounds like fringe science, but a deeper look makes it clear that the science is legitimate and the potential is huge. Owens and his team initially implemented BFR therapy in the limb salvage population to combat delayed amputations and to complement a dynamic exoskeleton, the Intrepid Dynamic Exoskeletal Orthosis (IDEO) now called the ExoSym, Hanger, Austin, Texas. BFR has a strong potential application for individuals post-amputation during the pre-prosthetic therapy phase. Implementing BFR treatment during pre-prosthetic therapy will help patients maintain the necessary strength for prosthetic use. It will lay the groundwork for the motor learning and skill acquisition that occurs in the early therapy sessions once the prosthesis is received. BFR therapy works by means of a specialized tourniquet system placed at the proximal portion of an injured limb. The cuff is inflated to a set/precise pressure while the patient performs low-load lifts (mechanical stress). The cuff restricts blood flow back to the heart (venous) but allows some oxygenated blood (arterial) into the muscle. The technique creates an oxygen-depleted environment, rapidly taking the muscle to failure. The venous blood pooled in the limb causes a buildup of metabolites (lactate, hydrogen ions, and inorganic phosphate) that are linked to muscle growth. BFR therapy provokes a physiological response from the body by replicating the environment that comes with high intensity exercise. BFR essentially tricks the body into believing it is working at a much higher capacity than it actually is, triggering an "anabolic cascade" to stimulate muscle growth.<sup>5,6,7</sup> Current research in the United States is examining the effects of BFR in injured populations who exhibit muscle and strength loss due to Achilles tendon ruptures, ACL injuries, femur and wrist fractures, rotator cuff injuries, osteoarthritis, total joint arthroplasty, and regenerative medicine procedures. BFR studies have shown statistically significant increases in muscle growth, yielding results/benefits in hypertrophy and strength comparable to those using much heavier weights. From the perspective of a physical therapist, Owens says this is a significant benefit because "using traditional approaches patients gain strength slowly."<sup>4</sup> Researchers around the world are also studying the effect of BFR on non-communicable diseases (diabetic, dysvascular, cancer) and in the geriatric populations. The physiological response created by BFR facilitates growth hormone release and angiogenic response, generating capillary beds, activating satellite cell (muscle stem cell), and enhancing protein synthesis. Increasing capillary bed density in the diabetic dysvascular population could have a major impact on positive outcomes.<sup>4</sup> Much more research and understanding is needed. Owens originally used BFR in the limb salvage and traumatic limb loss populations to quickly increase strength in these severely detrained populations. Increased musculature provides a prosthetic or orthotic device user better control and enables him or her to move more safely and efficiently. Increased strength also allows the user to more quickly learn the skills required to use a prosthesis or orthosis, which will increase activity levels and functional independence and return the individual to a higher quality of life. Before BFR therapy can be embraced fully in O&P, much more needs to be understood. The risks could be much greater in the diabetic dysvascular populations and there are often other comorbidities to consider. A physician's clearance would be needed before allowing participation, and participants must be monitored closely during therapy. Other potential risks include nerve damage if proper monitoring pressure with proper system is not used.<sup>4</sup> <em>John Pope, CPO, MPO, MS, CSCS, is a clinician at Hanger Clinic Lafayette Center, Washington DC.</em> <strong>References</strong> <ol> <li><em>Li, R., J. Xia, X. I. Zhang, W. G. Gathirua-Mwangi, J. Guo, Y. Li, et al. 2018. Associations of muscle mass and strength with all-cause mortality among US older adults. Medicine and science in sports and exercise 50(3), 458.</em></li> <li><em>Morris, D. R., A. J. Rodriguez, J. V. Moxon, M. A. Cunningham, M. M. McDermott, J. Myers, et al. 2014. Association of lower extremity performance with cardiovascular and all-cause mortality in patients with peripheral artery disease: a systematic review and meta-analysis. Journal of the American Heart Association 3(4), e001105.</em></li> <li><em>Newman, A. B., V. Kupelian, M. Visser, E. M. Simonsick, B. H. Goodpaster, S. B. Kritchevsky, et al. 2006. Strength, but not muscle mass, is associated with mortality in the health, aging and body composition study cohort. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 61(1), 72-77.</em></li> <li><em>Nutter, D., host. "Johnny Owens, MPT Talks Blood Flow Restriction Training." The Prosthetic Paradigm (podcast). December 10, 2018. <a href="https://opedge.dev/5136">https://prostheticparadigm.libsyn.com/johnny-owens-mpt-talks-blood-flow-restriction-training</a>.</em></li> <li><em>Patterson, S. D., L. Hughes, S. Warmington, J. Burr, B. R. Scott, J. Owens, et al. 2019. Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety. Frontiers in Physiology, 10:533.</em></li> <li><em>Schoenfeld B. J. 2013. Potential mechanisms for a role of metabolic stress in hypertrophic adaptations to resistance training. Sports Medicine 43(3):179-94.</em></li> <li><em>Vogel, J., D. Niederer, G. Jung, K. Troidl. 2020. Exercise-Induced Vascular Adaptations under Artificially Versus Pathologically Reduced Blood Flow: A Focus Review with Special Emphasis on Arteriogenesis. Cells 9(2), 333.</em></li> </ol>
