Many people wonder how blood flow restriction can be so effective at loads as light as 20-40% 1 RM in producing similar gains in muscle mass and (to a lesser extent) strength as heavier load (60-70+% 1RM) protocols.
It all comes down to understanding three main concepts: the force-velocity (FV) curve, fatigue and the effect of fatigue on muscle activation patterns.
As we introduce our blog to the fitness and rehab community, the BFR Pros is excited to announce that our inaugural blog posts will be focused on breaking down the science behind blood flow restriction.
Concept 3: Muscle Activation Patterns
Muscle activation increases with effort. Effort increases by increasing loads or by accumulating fatigue. During light load lifting without fatigue, the lower threshold motor units are the ones responsible for lifting the weight. If one increases the speed by increasing the effort of the muscle contraction, the higher threshold motor units will be recruited but at a very high shortening speed, reducing effectiveness of the stimulus. Conversely, if the weight is artificially slowed down, effort reduces, muscle activation drops and the only stimulation occurring is the type I muscle fibers of the low-threshold motor units. In order to be effective, low-load training must lead to significant fatigue accumulation to create beneficial adaptations in muscle mass and strength. Specifically, when continuing to lift light loads, metabolic byproducts accumulate which signal to the body that a stressful exercise is taking place, leading to the perception of pain and an increased effort to perform additional contractions. When new muscle fibers get recruited, it eventually leads to an increase in muscle activation as more of the higher threshold motor units become recruited to allow for continuation of the activity. Due to the fatigue, these muscle fibers can not move that weight at a very high speed, which allows for maximum force to be generated by each of the activated muscle fibers.
This is why low-load blood flow restriction training works. It increases fatigue to ultimately increase muscle activation at slow shortening speeds to produce muscle growth.
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