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. Glutes Gluteal Muscles (Glutes) are one of the strongest muscles in the body and are the connecting point between your legs and back muscles. Glutes are used in a variety of actions from moving the leg to extending and rotating the hip, as well as extending and rotating the trunk of the body. 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 the back extension rack with your back straight and your hands paced at the side of your head. Step 2 Lower your body down on the rack and gently stretch out your lower back. Step 3 Lift your body back up to the starting position using the muscles of your lower back and repeat.