Researchers have identified the role of the large Maf transcription factor family in regulating fast twitch muscle fibers. A mouse model lacking Maf expression in the skeletal muscles exhibited a significant loss of type IIb myofibers, a subtype of fast twitch fibers. Overexpression of large Mafs promoted type IIb muscle fiber induction. The large Maf family may represent potential targets for developing treatments for muscular disorders involving fast twitch fibers.