Epicatechin is a bioactive flavanol found in trace amounts in green tea and cocoa. Research with epicatechin indicates that it increases levels of follistatin, a unique type of protein found in the muscle cells which binds to and inhibits the actions of myostatin in the body. Epicatechin increases follistatin and more follistatin equals less myostatin, which in turn means more muscle.
Animals lacking myostatin, either due to a defective gene or because they’ve been treated with compounds that inhibit production, show huge increases in muscularity. The limits of muscle growth are removed by the inhibition of myostatin.