Proprioception is your body's ability to sense where your different parts are and what they're doing without having to look at them. Right now, even with your eyes closed, you know whether your arms are by your sides or raised above your head. You know if your legs are crossed or stretched out. That's proprioception at work.

This sense comes from special sensors in your muscles, tendons, and joints that constantly send messages to your brain about position and movement. When you walk down stairs while carrying a stack of books, proprioception helps you place each foot safely without staring at your feet the whole time. When you reach into your backpack without looking, proprioception guides your hand to find your pencil case.

Athletes rely heavily on proprioception. A gymnast doing a backflip knows exactly where her body is in the air. A basketball player dribbling down the court doesn't need to watch the ball bounce because proprioception tells him where his hand is in relation to the ball.

You can test your proprioception by touching your nose with your eyes closed. Your finger finds its target because proprioception tracks both where your nose is and where your moving finger is in space. Without this sense, even simple movements would require intense concentration and constant visual monitoring. Proprioception is sometimes called the “sixth sense” because it works so automatically that most people never even realize they have it.