Conditioned pain modulation (CPM) a measure of the effectiveness of the descending pain pathway and therefore a measure of the body's ability to perform endogenous analgesia. In subjects with normal function of the descending pain pathway, the net-effect during CPM testing is anti-nociceptive, or inhibition of the ascending pain pathway. In those with impaired descending pain pathway function, the response to CPM testing is pro-nociceptive, indicating that the body is unable to inhibit the pain signal, or may even amplify it. There is literature that supports the presence of impaired CPM, and therefore impaired descending pain pathway function, in numerus chronic pain conditions, including low back pain. Impaired descending pain pathway function may be contributing to this chronic pain presentation. This study will give us information on whether a typical physical therapy plan of care is able to improve impaired CPM, and if CPM values are predictive of improvement in physical therapy.