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. Back (middle) Middle back muscles are very important as they help to support and strengthen the core muscles at the front of your body. Exercise Instructions Step 1 Start on your back with your hands by your side. Step 2 Pull your leg up and cross it over your body until you feel a gentle stretch through your lower back. Step 3 Hold the stretching position for 15-20 seconds and then repeat on the other side.