Specifically, microCT analysis of femurs showed that r-irisin administration preserved both cortical and trabecular bone mineral density (BMD), as well as protecting against muscle mass decline, suggesting the irisin-based therapy development as a viable strategy for both elderly patients with osteoporosis and immobile physical disabilities and astronauts subjected to microgravity-induced bone and muscle loss. Here, FNDC5 is linked to osteoporosis.