Rapamycin helps 'rejuvenate' some muscles in old mice but not others—turns out, it depends on the muscle and how connected it is to nerves. In muscles that are more affected by aging, the drug might actually make nerve-related problems worse.

Older mice with overactive mTORC1 had higher levels of certain muscle-related amino acid processes after taking rapamycin, which might help muscles handle stress and stay healthy.

Giving older mice a drug called rapamycin helps keep their muscles strong and working well as they age, especially in some muscles but not others.

Taking rapamycin with exercise might help improve muscle strength in older people by affecting a specific cell pathway in the body.

As mice get older, a key cellular switch called mTORC1 in their muscles turns down genes that keep muscle structure strong, turns up genes linked to inflammation, and flips on signals seen when nerves stop talking to muscles. Giving them a drug called rapamycin helps reverse some of these changes, suggesting this switch plays a big role in how muscles age.

As we get older, a protein in our muscles called mTORC1 can become overactive, which slows down the body's cleanup process for damaged parts inside cells. Taking rapamycin might help turn that cleanup process back on.