Mitochondrial biogenesis is the process by which cells increase mitochondrial numbers.[1][2] It was first described by John Holloszy in the 1960s, when it was discovered that physical endurance training induced higher mitochondrial content levels, leading to greater glucose uptake by muscles.[3] Mitochondrial biogenesis is activated by numerous different signals during times of cellular stress or in response to environmental stimuli, such as aerobic exercise.[1][2][4]