What it is
Epicatechin is a flavanol found in cocoa, dark chocolate, green tea, apples, grapes, and other plant foods. Supplement discussions usually focus on (-)-epicatechin, but labels can blur together purified (-)-epicatechin, green tea extracts, cocoa flavanols, and related catechins.
Mechanism
The appeal is a cluster of plausible mechanisms: nitric oxide and endothelial function, mitochondrial signaling, antioxidant and redox effects, and the muscle-growth story around lower myostatin and higher follistatin. Those mechanisms are interesting, but they are not the same thing as a reliable training outcome.
Human evidence
The cleanest human signal is vascular, especially acute endothelial-function markers. The muscle signal is thinner. There are small or indirect studies showing changes in grip strength, myostatin, follistatin, or muscle-function markers, but much of that work is short-term, uses older or clinical populations, or uses extracts that are not isolated Epicatechin.
Performance data
The direct exercise-performance data is not convincing. In one human cycling-training study, 200 mg per day of 98% pure (-)-epicatechin did not improve anaerobic adaptations, did not reduce myostatin gene expression, and appeared to blunt relative VO2 peak and a mitochondrial adaptation marker compared with placebo. Another acute study found no added vasodilation or high-intensity performance benefit.
Dose context
The product I used listed 1,000 mg of Epicatechin per two-capsule serving from green tea extract. That is higher than the 25-200 mg per day range used in many purified-human studies, so I treated the label amount as real but did not assume that higher meant better.
Safety boundary
Short-term studies generally report good tolerance, but that is not the same as long-term safety at high supplemental doses. Because the goal was not to correct a deficiency or treat a disease, the bar for keeping it in the routine needed to be an observable benefit.