In addition, adaptation to increased contractile activity involves conversion from type II (fast twitch) to type I (slow twitch) fibers [18], a process also shown to be driven by PGC-1α in transgenic animals [16], while muscle-specific knock out of PGC-1α in animals has been shown to lead to conversion from type I to type II muscle fibers, exercise intolerance, decrease in mitochondrial proteins and myopathy [19]. Here, PPARGC1A is linked to myopathy.