Mitochondria become dysfunctional during prolonged inactivity and demonstrate increased mitochondrial fission, decreased mitochondrial proteins, decreased mitochondrial protein import, and decreased cardiolipin. See text for more details. FIS1, mitochondrial fission 1; OPA1, optic atrophy 1; MFN, mitofusins; DRP1, dynamin related protein 1; PGC-1α, peroxisome proliferator-activated receptor gamma coactivator 1-alpha; TFAM, mitochondrial transcription factor A.