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.
In the case of knee pain and instability, you will likely be placed in the seated position during testing and then asked to bend and straighten your leg under varying degrees of resistance. With performance testing, the speed of movement can be as important as relative strength, so you may have to repeat the movements several times while the equipment controls how fast you complete the task (this is called isokinetic testing).
A report with the data will be generated and your physician will then interpret it. After reviewing the results, a treatment program can be developed. While this may include the use of physical therapy for strength building, muscle re-education or stretching, correction of the cause for the deficits should also be addressed whenever possible.
Performance testing is rarely used in isolation; the findings have to be correlated to your personal history, physical examination, and other diagnostic findings. Nonetheless, the information obtained by performance testing may be exactly what is needed to correct problems concerning pain, weakness, or numbness and this category of evaluation should not be overlooked.