Epicatechin’s most remarkable effect is on the myostatin-follistatin axis. Myostatin is a protein secreted by muscles that acts as a “brake” on muscle growth – individuals or animals lacking myostatin develop significantly larger muscles. Epicatechin has been shown to increase follistatin levels by 2.5-fold and decrease myostatin levels by ~16–18% in human studies within days. Follistatin binds to myostatin and neutralizes it. Thus, higher follistatin means myostatin’s muscle-growth inhibition is reduced, allowing muscles to grow larger and stronger than normally possible. In one study, middle-aged men taking ~150 mg epicatechin per day for a week saw follistatin jump ~49% and handgrip strength increase 7%. Besides this myostatin pathway, epicatechin also boosts nitric oxide (NO) production via endothelial cells, improving blood flow. A mouse study showed epicatechin-treated mice had increased treadmill running endurance and muscle capillarity akin to having exercised, despite being sedentary. It appears epicatechin can partially mimic exercise by improving muscle blood supply and endurance. Additionally, epidemiological studies link high epicatechin intake to improved health: Harvard research noted reduced risk (~10%) of stroke, heart disease, diabetes, and cancer in those consuming epicatechin-rich foods (like dark chocolate) regularly. This likely stems from epicatechin’s antioxidant and blood flow-enhancing properties – it improves vascular function and reduces blood pressure modestly. In summary, epicatechin removes muscular growth limits via myostatin inhibition and simultaneously enhances endurance and cardiovascular health via NO elevation and antioxidant effects. These far-reaching actions make it a powerful natural supplement for muscle building, performance, and health.