Skeletal muscles do more than stabilize joints and power movement. They also act as an endocrine organ, releasing hundreds of chemical messengers that travel through the body and help protect other organs when we exercise. To harness this function, researchers turned a tiny muscle sample from a mouse’s thigh into a living graft, grew it in the lab and injected it under the skin on the mice’s backs. The cells developed their own blood vessels and formed muscle grafts that remained at the injection site.

Once implanted in elderly and obese mice, these grafts countered age-related muscle wasting. The mice developed thicker natural leg muscles, lost less muscle and showed improved strength and reduced inflammation.