Updated: November 21, 2008

You might think: Core generally refers to your abdominal muscles.

You should know:This term also includes the muscles that run up the back and stretch down to the butt and the front and inner thighs, says Michele Olson, PhD, professor of physical education and exercise science at Auburn University–Montgomery, Alabama. This group of muscles is where much of the bodys strength comes from; you use it to kick a ball, lift a heavy box, and even stand up straight.

You can work it: Pilates or yoga can strengthen the core, and many gyms are starting to offer core-based workouts. On your own, try Bicycle Crunches: Lie on your back, put both hands behind your head, and then draw your right elbow and left knee together, extending the right leg; switch and draw the left elbow and right knee together.