The present invention relates to fibronectin-based scaffold domain proteins that bind to myostatin. The invention also relates to the use of these proteins in therapeutic applications to treat muscular dystrophy, cachexia, sarcopenia, osteoarthritis, osteoporosis, diabetes, obesity, COPD, chronic kidney disease, heart failure, myocardial infarction, and fibrosis. The invention further relates to cells comprising such proteins, polynucleotides encoding such proteins or fragments thereof, and to vectors comprising the polynucleotides encoding the proteins.本發明係關於結合至肌肉生長抑制素以纖維連接蛋白為主之支架結構域蛋白質。本發明亦關於此等蛋白質在治療性應用中治療肌肉萎縮症、惡病質、少肌症、骨關節炎、骨質疏鬆症、糖尿病、肥胖症、COPD、慢性腎病、心臟衰竭、心肌梗塞及纖維化之用途。本發明進一步關於包含該等蛋白質之細胞、編碼該等蛋白質或其片段之聚核苷酸及包含編碼該等蛋白質之聚核苷酸的載體。