MSTN and sarcopenia: Several clinical trials are underway to develop therapeutic drugs for sarcopenia, targeting androgen receptor as well as myostatin,5,6 but there have not been any drugs yet approved for the improvement of the muscle loss that occurs in sarcopenia.7 There are a variety of drugs for the treatment of bone loss: vitamin D3, teriparatide, selective estrogen receptor modulators (SERMs), bisphosphonates, denosumab and romosozumab.8,9 Although sarcopenia and osteoporosis often coexist,10,11 most of these drugs exert effects only on bone.