This is 99% invisible. I'm Roman Mars.

This is starting up.

What I'm going to have you do when you get on.

I'm going to have you just stand for a few seconds

and then when I tell you to run.

That is the sound of producer Phoebe Flanagan jogging on a treadmill.

She's being observed by Lejeen Lawson, one of the world's leading experts on sports bras.

Lawson uses all kinds of fancy equipment like a 3D imaging machine to understand

the biomechanics of breasts and how they move when women exercise.

The breast will rise up and that has to go down again.

It changes direction constantly.

The accelerations, which is either speeding up or slowing down where the nipple is changing direction can be very high.

I did a research and I said, you know, a 36D nipple can go from 0 to 60 faster than a Ferrari.

Really?

Much faster.

Okay, let's see.

For the past 30 years, Lawson has worked as a researcher and consultant to champion athletic wear.

She specializes in sports bra design.

Sports bras are a piece of clothing that women might take for granted today, but they were totally

revolutionary when they were first invented.

They opened up whole new realms of sports and exercised women.

Not just because I've spent 33 years studying it, do I say this, I know from conversations with

...