TFAM and Mitochondrial myopathy: In this study, we used fast-twitch muscle fiber-specific Tfam KO mice and showed that this mouse model presents a disease progression similar to that observed in mitochondrial myopathy patients; that is, an initial decline in mitochondrial oxidative capacity accompanied by a faster force decline during repeated contractions (i.e. accelerated development of muscle fatigue), which is followed by a progressive decrease in force production in the unfatigued state (i.e. muscle weakness), reduction of bodyweight and premature death.