Hypertrophy
Meta-Analysis
2018
Effects of exercise intensity during blood flow restriction training on muscle strength and hypertrophy: A meta-analysis
By Manoel E. Lixandrao, Carlos Ugrinowitsch, Rogerio Brito, Hamilton Roschel, Valmor Tricoli and Cleiton Augusto Libardi
Scandinavian Journal of Medicine & Science in Sports, 28(3), pp. 779-785
Abstract
<h2>Abstract</h2> <p><a href="/terms/blood-flow-restriction/" class="term-link" data-slug="blood-flow-restriction" title="Blood flow restriction">Blood flow restriction</a> (BFR) training—also termed occlusion training or KAATSU—involves the application of external pneumatic cuffs or elastic wraps to restrict venous outflow while partially maintaining arterial inflow during exercise, enabling low-load resistance training to elicit hypertrophic and strength adaptations typically associated with high-load training. The capacity of BFR training to promote meaningful muscle growth at exercise intensities as low as 20–40% of <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="one-<a href="/terms/repetition-maximum/" class="term-link" data-slug="repetition-maximum" title="repetition maximum">repetition maximum</a>">one-repetition maximum</a> (1RM) offers a promising alternative for populations unable to tolerate conventional high-load training due to musculoskeletal injury, postoperative status, or joint pathology. The present <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> quantified the effects of exercise intensity during BFR training on measures of <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a> and strength across available controlled studies.</p> <p>A systematic search identified controlled studies comparing BFR training conditions at varying intensities with non-BFR low-load training and/or conventional high-load training. Random-effects meta-analyses were performed for measures of <a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="muscle CSA">muscle CSA</a>, thickness, and maximal strength.</p> <p>Results demonstrated that low-intensity BFR training (20–40% 1RM) produced significantly greater muscle hypertrophy and strength gains than low-intensity training without blood flow restriction. The hypertrophic effect of BFR training approached but did not fully equal that of high-intensity conventional training (60% 1RM). These findings support the clinical utility of BFR training as an effective low-load hypertrophic stimulus, particularly in populations where high <a href="/terms/mechanical-tension/" class="term-link" data-slug="mechanical-tension" title="mechanical loading">mechanical loading</a> is contraindicated. Optimal cuff pressure, exercise protocols, and safety parameters require further standardization [1].</p>Introduction
<h2>Introduction</h2> <p>The development of <a href="/terms/blood-flow-restriction/" class="term-link" data-slug="blood-flow-restriction" title="blood flow restriction">blood flow restriction</a> (BFR) training is largely attributed to the work of Yoshiaki Sato in Japan in the 1960s and 1970s, who pioneered a formalized approach termed KAATSU (加圧) training. Sato observed that restricting venous outflow from a limb during low-load exercise produced unusually marked hypertrophic and strength adaptations in the restricted muscles, suggesting a powerful interaction between the metabolic environment of relative ischemia and the hypertrophic signaling cascade [1]. Over subsequent decades, rigorous scientific investigation—particularly from Brazilian and Japanese research groups—began to characterize the physiological mechanisms and optimal parameters of BFR training, culminating in a substantial body of controlled experimental evidence.</p> <p>The conventional paradigm of resistance training for <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a> requires relatively high loads—generally ≥60–65% of <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>—to generate sufficient <a href="/terms/mechanical-tension/" class="term-link" data-slug="mechanical-tension" title="mechanical tension">mechanical tension</a> and <a href="/terms/metabolic-stress/" class="term-link" data-slug="metabolic-stress" title="metabolic stress">metabolic stress</a> to drive meaningful myofibrillar <a href="/terms/muscle-protein-synthesis/" class="term-link" data-slug="muscle-protein-synthesis" title="protein synthesis">protein synthesis</a> and muscle growth. This requirement creates significant practical barriers for populations in whom high mechanical loading is inappropriate: individuals recovering from orthopedic surgery, those with joint pathologies (osteoarthritis, tendinopathy), frail elderly individuals with low mechanical tolerance, and athletes managing overuse injuries while attempting to preserve muscle mass during rehabilitation. For these populations, a method capable of eliciting high-load-equivalent hypertrophic adaptations at low training loads would represent a major clinical advance [2].</p> <p>The proposed mechanisms by which BFR training at low loads achieves disproportionately large hypertrophic responses are multifactorial and incompletely understood. Venous blood pooling distal to the cuff elevates intramuscular metabolite concentrations (lactate, H⁺, inorganic phosphate), which may stimulate growth hormone release, metabolite-sensitive group III/IV afferents, and muscle swelling (cell volumization). Additionally, the partial hypoxic environment is thought to preferentially fatigue fast-twitch (Type II) motor units earlier than under normal circulatory conditions, thereby engaging high-threshold muscle fibers at loads that would not normally recruit them. Systemic anabolic hormone responses (GH, <a href="/terms/igf-1/" class="term-link" data-slug="igf-1" title="IGF-1">IGF-1</a>) are also substantially elevated following BFR training relative to low-load training without restriction [3].</p> <p>Given the expanding clinical and athletic interest in BFR training, a quantitative synthesis of <a href="/terms/dose-response-relationship/" class="term-link" data-slug="dose-response-relationship" title="dose-response">dose-response</a> data examining the role of exercise intensity within BFR paradigms—and relative to conventional training—is warranted. This <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a> was designed to provide such a synthesis.</p>Methods
<h2>Methods</h2> <h3>Search Strategy</h3> <p>Systematic searches were performed in PubMed/MEDLINE, EMBASE, CINAHL, and SPORTDiscus databases. Search terms included "<a href="/terms/blood-flow-restriction/" class="term-link" data-slug="blood-flow-restriction" title="blood flow restriction">blood flow restriction</a>," "BFR training," "occlusion training," "vascular occlusion," "KAATSU," "kaatsu," "ischemic training," combined with "<a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="muscle hypertrophy">muscle hypertrophy</a>," "<a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="cross-sectional area">cross-sectional area</a>," "muscle thickness," "muscle strength," "1 <a href="/terms/repetition-maximum/" class="term-link" data-slug="repetition-maximum" title="repetition maximum">repetition maximum</a>," and "resistance training." No date restrictions were applied. Hand searches of reference lists of relevant reviews and included articles supplemented database searches.</p> <h3>Eligibility Criteria</h3> <p>Studies were eligible <a href="/terms/intermittent-fasting/" class="term-link" data-slug="intermittent-fasting" title="if">if</a> they: (a) were peer-reviewed randomized controlled trials or controlled trials with human participants; (b) included at least one BFR training group performing exercise at low intensity (defined as ≤40% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>) with cuff or wrap application; (c) included at least one comparison group (low-load training without BFR and/or high-load training without BFR); (d) measured muscle hypertrophy (CSA, thickness, or volume) and/or maximal strength (1RM or isokinetic peak torque) at both baseline and post-intervention; and (e) provided sufficient data for <a href="/terms/effect-size/" class="term-link" data-slug="effect-size" title="effect size">effect size</a> computation. Studies employing passive BFR (no active exercise) were excluded, as were studies applying BFR to the trunk or studies without a non-BFR comparison group.</p> <h3>Data Extraction</h3> <p>Two reviewers independently extracted: sample characteristics (n, age, sex, training status), BFR protocol parameters (cuff width, occlusion pressure in mmHg or as % of arterial occlusion pressure), exercise load (<a href="/terms/relative-load/" class="term-link" data-slug="relative-load" title="% 1RM">% 1RM</a>), sets and repetitions, frequency, duration, and muscle group. Cuff pressure was recorded both as absolute mmHg values and, where available, as percentage of limb arterial occlusion pressure (AOP), a more physiologically meaningful metric. Primary outcome data (means, SDs, and group sizes) were extracted for hypertrophy and strength outcomes.</p> <h3>Statistical Analysis</h3> <p>Comparisons of interest were: (1) BFR low-load vs. low-load without BFR, and (2) BFR low-load vs. high-load without BFR. Hedges' g effect sizes with 95% confidence intervals were computed for each comparison. <a href="/terms/concentric-contraction/" class="term-link" data-slug="concentric-contraction" title="Positive">Positive</a> effect sizes indicated superiority of BFR training (for comparison 1) or of high-load training (for comparison 2). Random-effects pooling was applied. Subgroup analyses examined outcomes by muscle group, cuff pressure (high vs. low AOP%), and training status [4].</p>Results
<h2>Results</h2> <h3>Study Inclusion</h3> <p>The initial search yielded 2,143 records. After deduplication and title/abstract screening, 87 full-text articles were assessed for eligibility. Twenty-one studies met all inclusion criteria and were included in the <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a>. These studies enrolled a combined 441 participants (mean age 24.1 years; 64% male; 78% untrained or recreationally active). Cuff occlusion pressures ranged from 80 to 230 mmHg, with AOP percentages ranging from 40% to 90% where reported. <a href="/terms/blood-flow-restriction/" class="term-link" data-slug="blood-flow-restriction" title="BFR">BFR</a> training loads ranged from 20% to 40% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a>, and program durations ranged from 4 to 12 weeks [1].</p> <h3>BFR Low-Load vs. Low-Load Without BFR (<a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="Hypertrophy">Hypertrophy</a>)</h3> <p>BFR training produced significantly greater muscle hypertrophy compared with low-load training without blood flow restriction (Hedges' g = 0.59, 95% CI: 0.38–0.80, p 0.001; I² = 31%). In absolute terms, BFR training groups gained an average of approximately 7.2% more muscle thickness or <a href="/terms/cross-sectional-area/" class="term-link" data-slug="cross-sectional-area" title="CSA">CSA</a> compared with low-load controls. This effect was consistent across muscle groups (elbow flexors, quadriceps, and plantar flexors) and training statuses [2].</p> <h3>BFR Low-Load vs. High-Load Without BFR (Hypertrophy)</h3> <p>High-load conventional training (60% 1RM) produced numerically greater hypertrophy than BFR low-load training, but the difference was small and statistically non-significant (Hedges' g = −0.23, 95% CI: −0.48 to 0.02, p = 0.07). This finding indicates that BFR training approaches but does not fully equal the hypertrophic potency of high-load training, with a nonsignificant trend favoring conventional training. Within individual studies showing larger samples, the gap between BFR and high-load training was consistently narrow.</p> <h3>Strength Outcomes</h3> <p>For maximal strength measures, a <a href="/terms/squat-depth/" class="term-link" data-slug="squat-depth" title="parallel">parallel</a> pattern emerged. BFR training produced significantly greater strength gains than low-load training without BFR (g = 0.49, 95% CI: 0.27–0.71, p 0.001). Compared with high-load training, BFR training produced somewhat smaller strength gains, with a moderate difference favoring high-load training (g = −0.37, 95% CI: −0.62 to −0.12, p = 0.004), reflecting the principle of training specificity for maximal strength [3].</p> <h3>Cuff Pressure Subgroup Analysis</h3> <p>Studies using higher cuff pressures (≥60% AOP) produced larger hypertrophic effects than those using lower pressures (60% AOP) (g = 0.69 vs. g = 0.43, p for subgroup difference = 0.04), suggesting that adequate venous occlusion is important for maximizing the BFR hypertrophic response.</p>Discussion
<h2>Discussion</h2> <h3><a href="/terms/blood-flow-restriction/" class="term-link" data-slug="blood-flow-restriction" title="BFR">BFR</a> Training as a Viable Low-Load Hypertrophic Stimulus</h3> <p>The principal finding of this <a href="/terms/meta-analysis/" class="term-link" data-slug="meta-analysis" title="meta-analysis">meta-analysis</a>—that BFR training at 20–40% <a href="/terms/one-repetition-maximum/" class="term-link" data-slug="one-repetition-maximum" title="1RM">1RM</a> produces significantly greater <a href="/terms/muscle-hypertrophy/" class="term-link" data-slug="muscle-hypertrophy" title="hypertrophy">hypertrophy</a> than equivalent low-load training without blood flow restriction, while approaching the efficacy of high-load conventional training—establishes BFR as a genuinely effective hypertrophic training modality rather than a theoretical curiosity. The moderate <a href="/terms/effect-size/" class="term-link" data-slug="effect-size" title="effect size">effect size</a> favoring BFR over low-load training (g = 0.59) represents a practically meaningful difference that justifies the procedural complexity of BFR application in appropriate clinical and athletic contexts [1].</p> <p>The mechanisms underlying this hypertrophic advantage are likely multifactorial. The hypoxic, metabolite-rich environment created by venous restriction appears to accelerate muscular fatigue and <a href="/terms/motor-unit/" class="term-link" data-slug="motor-unit" title="motor unit">motor unit</a> recruitment, effectively compelling the recruitment of fast-twitch Type II fibers at loads that would otherwise engage predominantly slow-twitch units. This fast-twitch recruitment at low mechanical loads is a particularly compelling feature of BFR training, as Type II fibers possess greater hypertrophic potential and are typically inaccessible at low training intensities. Concurrent elevations in systemic growth hormone, local <a href="/terms/igf-1/" class="term-link" data-slug="igf-1" title="IGF-1">IGF-1</a> splice variants, and <a href="/terms/mtor/" class="term-link" data-slug="mtor" title="mTORC1">mTORC1</a> pathway activity likely amplify the hypertrophic signal [2,3].</p> <h3>Clinical Applications</h3> <p>The inability to tolerate high mechanical loads is a common clinical scenario. Postoperative patients following ACL reconstruction, total knee arthroplasty, or rotator cuff repair often lose substantial muscle mass during extended immobilization and restricted activity periods. BFR training at low loads enables exercise-induced muscle preservation and even hypertrophy in these contexts without imposing the joint stress associated with conventional high-load rehabilitation. Similarly, older adults with significant osteoarthritis, individuals with chronic tendinopathy, and patients with stress fractures may benefit from BFR training as a primary or supplementary modality.</p> <h3>Practical Protocol Considerations</h3> <p>For practitioners implementing BFR training, several protocol parameters warrant attention based on the current evidence. Cuff pressure should achieve at least 40–60% of AOP to produce meaningful venous restriction; pressures below this threshold appear to produce attenuated benefits. Common clinical practice involves 4 sets with repetition schemes of 30-15-15-15 to volitional failure at 20–30% 1RM, with 30–60 second <a href="/terms/inter-set-rest-interval/" class="term-link" data-slug="inter-set-rest-interval" title="inter-set rest">inter-set rest</a> periods. Elastic wrap-based BFR (as opposed to pneumatic cuffs) provides a lower-cost alternative, though standardization of occlusion pressure is more difficult [4].</p> <h3>Safety Considerations</h3> <p>The safety profile of appropriately applied BFR training is favorable in healthy individuals, with transient discomfort, petechiae, and <a href="/terms/delayed-onset-muscle-soreness/" class="term-link" data-slug="delayed-onset-muscle-soreness" title="delayed onset muscle soreness">delayed onset muscle soreness</a> being the most commonly reported side effects. Absolute contraindications include deep vein thrombosis history, severe peripheral arterial disease, lymphedema, and open wounds in the occluded limb. Clinicians should obtain appropriate training and supervise initial BFR sessions in clinical populations. The dose of mechanical compression should be individually calibrated when possible, as limb circumference and tissue compliance substantially affect the occlusion pressure achieved at any given cuff pressure [1,4].</p>관련 논문
근비대
2017
신장성 vs. 단축성 저항 훈련: 근비대에 관한 체계적 문헌고찰 및 메타분석
14개 공유 용어
근비대
2017
주간 저항 훈련 볼륨과 근육량 증가 사이의 용량-반응 관계: 체계적 문헌고찰 및 메타분석
14개 공유 용어
근비대
2019
저항 훈련 볼륨은 훈련된 남성에서 근비대를 촉진하지만 근력은 아니다
12개 공유 용어
근비대
2022
저항 훈련에서 실패 근접도가 골격근 비대에 미치는 영향: 메타분석을 포함한 체계적 문헌고찰
12개 공유 용어
근비대
2015
건강한 고령자에서 저항 훈련의 용량-반응 관계: 체계적 문헌고찰 및 메타분석
12개 공유 용어