As the results of the cross‐sectional experiments described above suggest that PolgA mice display clear signs of co‐existing osteopenia and sarcopenia from 40 weeks onwards, we aimed to longitudinally track individual mice during the transition from young to frail status in order to gain a better understanding of when exactly and to what extent bone loss (osteopenia) occurs in individual mice. The gene discussed is POLG; the disease is sarcopenia.