Just like the stressors of life, the stress of arthritis can cause you to feel out of control. Yet, the most powerful way to help regain the strength and independence painful joints can take away is to turn toward your bodys core.The core is actually a large group of muscles that you should imagine as a box of tools, says Cleveland Clinic Florida physical therapist Kristin Miller, DPT. The top of the box is the diaphragm part of your torso. The sides are the hip muscles and the oblique muscles on the trunk, says Miller. The back is made up of the back extensor muscles, the bottom is the pelvic floor and the front is the abdominal muscles. All of these muscles need to be working properly and balanced in order to have stable back muscles. If any are not doing their job or if balance is disrupted, pain in the back and other areas can be increased.