![]() These metabolites interfere with the excitation–contraction mechanism causing earlier recruitment of type 2 muscle fibers relative to the same exercise being performed in free-flow conditions ( 22,98). Byproducts of muscular contractions such as lactate, hydrogen ions (H+), ATP, and inorganic phosphates are produced and are unable to exit the limb through the venous system due to the restrictive cuff ( 56). Metabolite-induced accelerated fatigue describes the phenomena that occur when BFR is applied to an exercising limb. Both mechanisms have the capacity to create an anabolic environment in the muscle to augment MPS responses to exercise and are discussed in the following subsections. RESISTANCE TRAINING: MECHANISMS UNDERLYING HYPERTROPHYĬurrent theory proposes 2 primary mechanisms underlying the benefits observed with low-load RT with BFR: metabolite-induced accelerated fatigue and cellular swelling. Thus, it seems that mTORC1 expression is crucial to the long-term hypertrophic response to BFR training regardless of the exact mechanisms that differentiate low-load BFR versus high-load traditional training. Finally, administering mTORC1's antagonist, rapamycin, blunts the muscle protein synthesis (MPS) response to BFR exercise, highlighting the importance of this pathway during BFR exercise ( 36). ![]() However, low-load exercise that is work-matched to BFR (i.e., 30-15-15-15 repetitions) does not appreciably increase mTORC1 levels nor alter mTORC1 downstream protein kinase molecules such as S6 kinase beta-1 (S6K1), and thus, these protocols are inferior in producing appreciable gains in muscle size ( 32,33), conceivably because the intensity of effort is not sufficiently challenging to evoke a robust hypertrophic stimulus. Both heavy- and light-load training, with and without BFR, performed to volitional failure have shown to induce significant mTORC1 expression and, in longitudinal studies, are reported to produce similar increases in muscle size in various populations ( 18,20,21,53). Sufficient stimulation of skeletal muscle via RT induces post-exercise increases in mTORC1 expression, eventually leading to visible increases in muscle size with continued training ( 32,63). Muscle growth appears to be mediated by mechanistic target of rapamycin complex 1 (mTORC1), a molecular nodal point in the anabolic molecular intracellular signaling pathway ( 36). Skeletal muscle hypertrophy occurs when net protein balance is positive, providing a favorable environment to induce muscle growth ( 16). The mechanisms underlying BFR RT are still contentious but appear to be somewhat modulated by similar processes as free-flow exercise. BLOOD FLOW RESTRICTION TRAINING MECHANISMS OVERVIEW (HYPERTROPHY FOCUSED) This article will provide an evidence-based review of current research on the resistance-training benefits of BFR exercise with respect to hypertrophy and draw practical conclusions as to how the strategy can be applied by physique athletes to optimize increases in muscle mass. ![]() Low-load RT with BFR can provide similar increases in muscle mass compared with heavier (70+% 1RM) lifting, making it an alternative for physique athletes seeking to maximize muscle growth without additional joint stress ( 21,53). Because of the unique metabolic environment in the limb from the compressive cuff, BFR training is commonly prescribed with loads as light as 20% one repetition maximum (1RM) ( 71). The reduction in blood flow from the applied pressure decreases oxygen delivery, challenging local energy metabolism and reducing the time needed to reach volitional failure during aerobic training and resistance training (RT) compared with similar exercise without restriction ( 27,28,99). As a result, blood pools in the extremity distal to the cuff, altering the local muscular environment. In the 54 years since his discovery, BFR training has been studied in hundreds of published articles and is used by a wide variety of populations-from the injured ( 29,40) to the physique athlete looking to maximize muscle growth during contest preparation ( 58).īFR training involves use of a compressive cuff wrapped around the proximal portion of the limb so as to partially reduce arterial flow and completely restrict venous return ( 71). Modern day blood flow restriction (BFR) training was discovered in 1966 by Yoshiaki Sato, who called it KAATSU (“added pressure”) training ( 76).
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