How it Works
Blood flow restriction training can elicit profound increases in muscle size with loads as low as 20% of an individual’s 1RM (one repetition maximum). With traditional resistance training (non-BFR), such light loads do not subject muscles to great enough mechanical tension to cause significant hypertrophy (in most cases). However, blood flow restriction cuffs create a physiological environment that unlocks muscle growth capabilities at low intensities. In simple terms: resistance training under BFR can help you put on muscle training with less weight!
With a mountain of research (including well-designed randomized controlled trials) demonstrating blood flow restriction’s efficacy in building muscle at light loads, the question now is not if it works, but how. Some of the mechanisms of BFR are yet to be understood completely (we know it leads to hypertrophy, but we can’t fully explain how). Below, we’ll explain a few of the primary proposed mechanisms of how blood flow restriction can create such profound results in muscle building.
- Hypoxia - This is a state of low oxygen. Research has shown that a low oxygen environment alone can stimulate muscle growth pathways. In the context of blood flow restriction, a hypoxic environment is created at the muscle as oxygen-carrying blood flow to the muscle is limited or occluded.
- Metabolite accumulation - Metabolites such as lactate build in the body during strenuous exercise. It is known that the presence of lactate at the level of the muscle can be a potent stimuli of muscle growth. With BFR cuffs occluding venous blood flow (the blood leaving the limb), lactate accumulates at an accelerated rate, which can stimulate hypertrophy.
- Cell swelling - The infamous “pump” from resistance training caused by accumulation of blood and metabolites at the working muscle can itself be hypertrophic (muscle building). When the cell wall stretches due to the swelling, receptors on the cell wall can trigger a cascade of anabolic pathways.
- High threshold motor unit activation - Likely for a combination of the reasons listed above (increased cell swelling, metabolite accumulation, hypoxia, ) training with light loads under BFR can stimulate high threshold motor units (the motor units typically only activated under very high intensities of 80+ % 1RM). In order to achieve maximal hypertrophy, it’s likely quite important not to neglect these high threshold motor units.
- Gene expression / Endocrine factors - A notable inhibitor of muscle growth called myostatin has shown to be significantly inhibited by blood flow restriction training (potentially to a greater degree than from traditional resistance training). This may partially explain why BFR is such a powerful stimulator of hypertrophy.
Though there are hundreds of peer-reviewed papers on blood flow restriction, the scientific community heavily values systematic reviews and meta-analyses, which examine data from multiple independent and high quality studies to determine overall trends. The below systematic review and meta-analysis includes twelve different studies examining the impacts of blood flow restriction on strength and muscle mass.
Magnitude of Muscle Strength and Mass Adaptations Between High-Load Resistance Training Versus Low-Load Resistance Training Associated with Blood-Flow Restriction: A Systematic Review and Meta-Analysis
“Regarding the hypertrophic response, results revealed similar effects between HL [high load] and BFR-RT [blood flow restricted resistance training]”
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