MUSCLES ENGAGED Back (middle) Middle back muscles are very important as they help to support and strengthen the core muscles at the front of your body. 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. Exercise Instructions Step 1 Start in a kneeling position on the floor with your back in a neutral position and your hands right your shoulders. Step 2 Reach through your opposite arm and leg and try to feel a stretch on the back on your shoulder and mid back. Step 3 Pull your arm back and open your chest up into a fly position trying to feel a stretch on the front of your shoulder and lower back.