Performance testing can be used to assess functional assessment. Sometimes there is not anything structurally or physiologically wrong with your body, but the way it is being used is the problem. For example, due to a relative strength deficit in your back muscles when you bend or twist, your abdominals are doing too much of the work. As a result of this imbalance, there is unnecessary torque on your spine, and pain may occur.
Performance testing uses various types of equipment to assess how you function. For your spine, you may be asked to sit in a device that will stabilize your pelvis (much like a seat belt holds you in your car seat), and then under varying amounts of resistance you will be asked to move back and forth or from side to side. A computer will analyze the quality of your movement, how consistent you are, and look for portions of your motion that have a glitch in it.