Introduction: Blood Flow Restriction (BFR) is widely used in exercise training to increase exercise-induced metabolic stress. Current research suggests that low-intensity exercise with BFR can yield comparable muscle benefits to high-intensity exercise. The potential underlying mechanism involves metabolic stress and by-product accumulation, leading to altered muscle activation and fibers recruitment. This immediate effect may assist athletes in their pre-exercise preparation. However, there is a lack of comprehensive understanding of the acute effects of BFR. Therefore, this study aims to (1) summarize the acute effects of BFR, and (2) discuss their clinical applications and recommendations. Methods: This study searched four databases for studies published between 2014 and February 2024 with keywords in groups of "effect" and "blood flow restrict*". Inclusion criteria were included: (1) a randomized controlled trial design, (2) interventions involving ischemic conditions applied to human extremities, and (3) studies measuring acute effects (within 24 hours after exercise) as outcome measurements following a single intervention, after the removal of BFR. Studies were selected based on the 2020 PRISMA guidelines and assessed for quality using the PEDro scale. Results: A total of 15 studies were included. The BFR intervention protocols used in the selected studies involved either continuous or intermittent compression, with BFR cuff applied to the proximal limb with pressures ranging from 40 to 260 mmHg systolic blood pressure or 30% to 80% of arterial occlusion pressure. Seven studies reported that BFR does not adversely affect hemodynamics acutely compared to control groups. Metabolic responses increase immediately after intervention in 3 of 6 studies, and 2 of 6 studies suggested that BFR facilitated recovery 24 hours post-exercise. Regarding muscle function, 2 of 5 studies observed increased muscle activation, while two others found a decreased in maximum strength performance immediately after exercise with BFR. Additionally, 3 studies reported changes in human soft tissue such as quadriceps and Achilles tendon, and 2 studies noted relief in musculoskeletal pain following exercise with BFR. Discussion: Exercise with BFR is safe for a variety of populations, as it does not have a negative impact on either individuals with or without cardiovascular conditions. Metabolic responses notably increase immediately when BFR is combined with exercise to exhaustion compared to regular exercise, suggesting that BFR likely requires sufficient exercise intensity to provide effective stimulation. The influence on muscle function likely stems from the hypoxic environment created by BFR, which facilitates greater recruitment of type II muscle fibers, potentially enhancing rapid force production, a factor found to be vital for injury prevention. This suggests that BFR could effectively and safely enhance the benefits of explosive muscle strength training with low intensity, offering benefits such as faster recovery and pain relief. Impact/Application to the field: BFR is a relatively safe method for enhancing the effects of exercise at lower intensities. Given its ability to stimulate metabolic responses, increase muscle activation, and relieve pain, it is recommended that BFR be incorporated into injury prevention and warm-up programs. This is particularly beneficial for populations experiencing insufficient muscle activation or musculoskeletal pain.
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