So what is all this talk about core and what exactly is “my core”? Your core is actually made up of 3 parts; your abdominal muscles, your trunk, and your shoulders. Of course everyone wants great abs, but sit ups are not the only way to get those muscles strong. Core means central and in order for the middle to be strong your arms and legs have to help stabilize you when doing some core work like a push up or a plank. Here are some more advanced core exercises that you can modify at your gym.