Remember when you used to feel athletic?

When you could move with power, recover fast, and trust your body to do what you asked of it. You used to have that. But at some point — you probably can't even say when — it started to slip.

Now you're stiff in the morning. You hesitate doing things that used to be automatic. You work out, but something still feels off. This isn't about how you look — you're not out of shape. You've lost something, and you know it.

You can feel it. You just can't measure it — because nothing ever has. Until now.