Contrary to what many people believe, your legs don't power you through movements, nor do your arms power you. Your brain isn't even what powers you. Your physical (and mental) power center is in your core. Right smack in the center of your body, around your belly button and abdominals; that's your core and that's where your power center is. These terms are used interchangeably in most cases because they're the same in location and function.

If you try to walk, balance, stand up from sitting, reach to a cabinet or any kind of common sports or daily-life movement, without your core engaged, you aren't able to move smoothly or strongly. No matter what you do, imagine its movement stems from your center, your power center, and not from the limb doing the action.