I'm William Brangham and this is Horizons.

We all know exercise is good for us, but how exactly does it impact the human body?

Does it change us at the molecular level?

And if so, how can we best harness its power?

Coming up next. Welcome to Horizons from PBS News. This will come as a surprise to no one. But exercise is really good for us. It's good for you. It's good for me.

It's good for everyone.

Shocking, right?

But why it works and how it works, those things are far less understood.

So we're going to spend this episode talking with a man who, along with a big team of others,

is trying to understand the profound impact that exercise can have.

He is part of a massive, decade-long, multi-site investigation to tease out how, at the very

molecular level, exercise changes our bodies and why. In describing this team's first series of

papers published in Nature two years ago, our guest wrote this about exercise.

Quote, its benefits in prevention outstrip any known drugs, 50% reduction in the risk of cardiovascular disease, 50% reduction in the risk of many cancers, positive effects on mental health, pulmonary health, GI health, bone health, muscle function.

He wrote, exercise may be the single most potent medical intervention ever known.

Stanford University's U.N. Ashley is a professor of genomics and cardiovascular medicine.

He's chair of the Department of Medicine,

and he's part of this research consortium working to understand the miracle intervention

that has been staring us in the face all along. You and Ashley, thank you so much for talking

with us today. As I mentioned, we all know exercise is good for us. So what are the questions that you and your

team are trying to tease out? Well, as you mentioned, William, the exercise is really the most

potent medical intervention we've ever known. But what's amazing is that we don't actually

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