THE PRESENT INVENTION PROVIDES ISOLATED HUMAN OR HUMANIZED ANTIBODIES OR ANTIGEN-BINDING FRAGMENTS THEREOF WHICH SPECIFICALLY BIND TO GROWTH AND DIFFERENTIATION FACTOR-8 (GDF8) AND BLOCK GDF8 ACTIVITY. THE ANTIBODIES AND ANTIBODY FRAGMENTS OF THE PRESENT INVENTION MAY BE USED IN THERAPEUTIC METHODS FOR TREATING CONDITIONS OR DISORDERS WHICH ARE AMELIORATED OR IMPROVED BY INHIBITION OF GDF8.
