Safety and Biomarker Response to (+)-Epicatechin in Becker Muscular Dystrophy

INCLUSION CRITERIA: 1. Participant must be ≥16 to \<60 years of age. 2. Genotype confirmation showing a mutation of the dystrophin gene. 3. Ambulation - participants must show a history of ambulation past the age of 16 years, with continued ambulation thereafter. 4. If on glucocorticoid treatment in the last 12 months, participants must be on a stable dose at screening. Participants cannot start steroids during the study. EXCLUSION CRITERIA: 1. A diagnosis of other neurological diseases or presence of relevant somatic disorders that are not related to Becker muscular dystrophy. 2. Participants with a history of migraine headaches requiring medical attention and active treatment within the past 6 months. 3. Participants with allergies to chocolate or cocoa. 4. Surgery or orthopedic injury that might affect muscle strength or function within 3 months before study entry or planned surgery at any time during the study. 5. Presence of a concomitant neurologic disease (e.g., Parkinson's disease) that could negatively impact mobility or balance. 6. Symptomatic heart failure (New York Heart Association Class III or IV) or known left ventricular ejection fraction \<40% by echocardiogram. 7. Presence of documented intrinsic lung disease (e.g., chronic obstructive pulmonary disease, pulmonary fibrosis). 8. Evidence of current liver disease or impairment. 9. Inadequate renal function. 10. Platelet count, WBC count, and hemoglobin at Screening \<Lower Limit of Normal (LLN). 11. Surgery or orthopedic injury that might affect muscle strength or function within 3 months before study entry or planned surgery at any time during the study