MYH14 and nemaline myopathy: As the force-generating capacity of muscle fibers depends on the myosin heavy chain isoform composition, we determined the relative abundance of slow myosin isoforms (MHCslow) and fast myosin isoforms MHC 2A and 2× (MHCfast) in the single fibers of control subjects and the muscle fiber bundles of NEB-NM patients that were used for the contractility experiments.