MUSCLES ENGAGED Back (lower) The lower back is often not trained because it is not visible in the mirror. If you have weak lower back muscles, there is nothing to help pull back against the spine, putting you at risk of developing poor posture (hunched over). Weak lower back muscles can also lead to lower back pain. Equipment Used Extention Rack A back extension rack is a piece of fitness equipment that helps to develop and strengthen the lower back and core. It can also help to develop secondary muscles, such as hamstrings and glutes. Exercise Instructions Step 1 Start in a prone position on the roman chair with your hands placed gently at the side of your head. Step 2 Perform a full back extension and when you are at the top, pause and then rotate to one side. Step 3 Perform another back extension and rotate to the other side.