16, 17, 18 However, greater motor unit recruitment is not limited to muscles distal to the area of occlusion. 7, 14, 15 In addition, type II fast-twitch muscle fibers, which are normally only preferentially recruited at greater intensity, are activated at lower loads under BFR conditions, providing rationale for the increased muscle hypertrophy in low-load BFR in comparison with similar low-load exercise alone. They are believed to induce earlier, peripherally mediated fatigue, resulting in greater motor unit recruitment, as suggested by the fact that BFR under low loads has similar recruitment to that of high load resistance training. 5, 6, 10, 11, 12, 13 Metabolites, which accumulate during exercise and are known mediators of muscular hypertrophy, are amplified by BFR’s relative ischemic and hypoxic conditions. 4, 5, 6, 7, 8, 9 At a cellular level, metabolites, hormonal differences, cell-to-cell signaling, cellular swelling, and intracellular signaling pathways have all been implicated. A number of mechanisms have been theorized, but currently it is believed that metabolic stress from vascular occlusion and mechanical tension from resistance training or exercise lead to synergistic increases in muscle hypertrophy and strength. Consideration also will be given to guidelines for safe implementation.īefore exploring the applications and practical guidelines for implementing BFR, it is important to understand its mechanism of action. 1, 2, 3 The purpose of this review is to highlight the physiology and evidence behind the various applications of BFR, with a focus on postoperative rehabilitation. This has uncovered multiple benefits beyond that of muscular growth, including improvement in muscular endurance, cardiovascular fitness, pain, and bone density. As awareness of BFR has grown so too has the knowledge behind its physiologic mechanism of action. Other novel forms being applied clinically also include BFR with aerobic exercise, passive application (i.e., BFR in the absence of exercise), and neuromuscular stimulation. Initially, this modality of rehabilitation gained notoriety for its use in wounded servicemembers with volumetric muscle loss and limb-salvage scenarios, but it has expanded across a number of applications, including regular strength training, postoperative rehabilitation, and atrophy prevention. Continued adherence to rehabilitation guidelines and exploration of BFRs physiology and various applications will help optimize its effect and prescription.īlood flow restriction (BFR) therapy, a controlled form of vascular occlusion combined with resistance training or exercise, has seen tremendous growth in recent years. New forms of BFR and expanding applications in postoperative patients and athletes hold promise for expedited recovery. While much remains to be learned, it is clear that blood flow restriction therapy stimulates muscle hypertrophy via a synergistic response to metabolic stress and mechanical tension, with supplemental benefits on cardiovascular fitness and pain. The purpose of this review is to highlight the physiology and evidence behind the various applications of BFR, with a focus on postoperative rehabilitation. There is also growing evidence to suggest that it augments cardiovascular fitness and attenuates pain. BFR represents a way to decrease stress placed on the joints without compromising improvements in strength, whereas for postoperative, injured, or load-compromised individuals BFR represents a way to accelerate recovery and prevent atrophy. Initially, this technique was seen as a way to stimulate muscular development, but improved understanding of its physiologic benefits and mechanism of action has allowed for innovative clinical applications. Blood flow restriction (BFR) is an expanding rehabilitation modality that uses a tourniquet to reduce arterial inflow and occlude venous outflow in the setting of resistance training or exercise.
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