Turning on a certain signal in mouse muscles makes them age faster, causing nerve and muscle problems like those seen in old age — but this can be reversed with a drug called rapamycin.

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.

Rapamycin might help older animals keep their muscle and stay lean by tweaking a key cell signal involved in aging.

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.

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.

When you lift weights, your muscles turn on a specific molecular switch called mTORC1, which helps build more muscle protein. But just because this switch flips on right after a workout doesn’t mean you’ll definitely get bigger muscles over time—it doesn’t always line up.