1) "The transverse and rectus abdominus -- those muscles that run from just below your sternum to your waist -- are definitely included in your core.
2) "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 ..."
3) "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."
4) "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."