Exercise in a pill

We all know exercise is good for us. It builds muscle, strengthens bones, lowers blood pressure, and boosts mood. By deciphering how movement benefits the body, researchers hope to develop medicines that can offer some of the same perks—without the workout. The idea isn’t to replace exercise but to bring its upsides to people who struggle with frailty, disability, or chronic illness.

The sticking points

It will take a lot of experimentation to untangle the myriad pathways by which exercise…