No matter what your fitness goals are, you'll hear a lot about the "core." Personal trainers advise core-strengthening exercises, and articles in fitness magazines come out with a new "core" exercise routine every month. You may have some vague notion that your core is somewhere in the middle of your body, right around your abs, and that's a close guess. Your core muscles make up pretty much all of your torso, and then some.
Yes, the transverse and rectus abdominus -- those muscles that run from just below your sternum to your waist -- are definitely included in your core. These muscles make it possible for you to perform every day activities, from housework to sports, by helping support your back when you bend over and stand up, and they work with other core muscles to assist with posture.
Some of your back muscles are considered part of the core muscle group. Your lower back and the outer-middle part of your back, sometimes called your "lats," are the back muscles that are also core muscles. Strong back core muscles support your abs and help you with actions like sitting up at your desk, bending to tie your shoe or reaching up to take something off a shelf.
Running down along your sides, from your ribs to your upper hips, are your obliques. These important core muscles help you twist and bend from side to side. They're necessary for a powerful swing in golf or tennis and are vital for turning your body for a view of what's behind you.
The muscles of the torso are typically the ones to come to mind when you think of your core, but they actually extend down into your legs. The core muscles of your upper body get support and assistance from your hip muscles. These include your hip flexors; abductors, along the outside of your thighs; and adductors, along the inside of your thighs. Even your hamstrings, which extend down the backs of your thighs, and your glutes -- together known as the hip extensors -- are considered core muscles. Without these muscles to assist the rest of your core, you'd find it difficult to sit down and stand up, lift heavy items or extend your legs.