A humanized antibody that specifically binds and antagonizes GDF-8, comprising: an antibody variable heavy region comprising a first, a second and a third complementarity determining region, and an antibody variable light region comprising a first, a second and a third complementarity determining region; wherein: said antibody binds to GDF-8 with a Kd of 10 -11 M or higher affinity; and wherein: the first CDR from a VH region has the amino acid sequence of SEQ ID NO:10, the second CDR from a VH region has the amino acid sequence of SEQ ID NO:11, the third CDR from a VH region has the amino acid sequence of SEQ ID NO:12, the first CDR from a VL region has the amino acid sequence of SEQ ID NO:13, the second CDR from a VL region has the amino acid sequence of SEQ ID NO:14, and the third CDR from a VL region has the amino acid sequence of SEQ ID NO:15; or wherein: the first CDR from a VH region has the amino acid sequence of SEQ ID NO:20, the second CDR from a VH region has the amino acid sequence of SEQ ID NO:21, the third CDR from a VH region has the amino acid sequence of SEQ ID NO:22, the first CDR from a VL region has the amino acid sequence of SEQ ID NO:23, the second CDR from a VL region has the amino acid sequence of SEQ ID NO:24, and the third CDR from a VL region has the amino acid sequence of SEQ ID NO:25. an antibody variable heavy region comprising a first, a second and a third complementarity determining region, and an antibody variable light region comprising a first, a second and a third complementarity determining region; wherein: said antibody binds to GDF-8 with a Kd of 10 -11 M or higher affinity; and said antibody binds to GDF-8 with a Kd of 10 -11 M or higher affinity; and wherein: the first CDR from a VH region has the amino acid sequence of SEQ ID NO:10, the second CDR from a VH region has the amino acid sequence of SEQ ID NO:11, the third CDR from a VH region has the amino acid sequence of SEQ ID NO:12, the first CDR from a VL region has the amino acid sequence of SEQ ID NO:13, the second CDR from a VL region has the amino acid sequence of SEQ ID NO:14, and the third CDR from a VL region has the amino acid sequence of SEQ ID NO:15; the first CDR from a VH region has the amino acid sequence of SEQ ID NO:10, the second CDR from a VH region has the amino acid sequence of SEQ ID NO:11, the third CDR from a VH region has the amino acid sequence of SEQ ID NO:12, the first CDR from a VL region has the amino acid sequence of SEQ ID NO:13, the second CDR from a VL region has the amino acid sequence of SEQ ID NO:14, and the third CDR from a VL region has the amino acid sequence of SEQ ID NO:15; or wherein: the first CDR from a VH region has the amino acid sequence of SEQ ID NO:20, the second CDR from a VH region has the amino acid sequence of SEQ ID NO:21, the third CDR from a VH region has the amino acid sequence of SEQ ID NO:22, the first CDR from a VL region has the amino acid sequence of SEQ ID NO:23, the second CDR from a VL region has the amino acid sequence of SEQ ID NO:24, and the third CDR from a VL region has the amino acid sequence of SEQ ID NO:25. the first CDR from a VH region has the amino acid sequence of SEQ ID NO:20, the second CDR from a VH region has the amino acid sequence of SEQ ID NO:21, the third CDR from a VH region has the amino acid sequence of SEQ ID NO:22, the first CDR from a VL region has the amino acid sequence of SEQ ID NO:23, the second CDR from a VL region has the amino acid sequence of SEQ ID NO:24, and the third CDR from a VL region has the amino acid sequence of SEQ ID NO:25.