As of right now we don’t really know. So far all we have are theories of how BFR causes muscle growth. One theory is the accumulation of metabolic stress. Metabolic stress is the increase by-products from muscle contraction. Typically, a training protocol using at least 12 reps will cause an increase in metabolic stress. Pair these high reps with short rest periods and your metabolic stress will be through the roof. Finally, the accumulation of metabolic stress activates hormones and signals which lead to muscle growth.
Another theory is that muscles become recruited and fatigue much faster during BFR compared to traditional resistance training. Does this mean you should perform all your training using BFR? No this is because BFR does not seem to increase strength compared to traditional resistance training. Since most people like strong I would only perform BFR periodically.
(2015). A review on the mechanisms of blood-flow restriction resistance training-induced muscle hypertrophy. Sports Medicine, 45(2), 187-200.
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